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Versions: (draft-schierl-payload-rtp-h265) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 7798

Network Working Group                                        Y.-K. Wang
Internet Draft                                                 Qualcomm
Intended status: Standards track                             Y. Sanchez
Expires: November 2014                                       T. Schierl
                                                         Fraunhofer HHI
                                                              S. Wenger
                                                                  Vidyo
                                                       M. M. Hannuksela
                                                                  Nokia
                                                           May 28, 2014




            RTP Payload Format for High Efficiency Video Coding
                    draft-ietf-payload-rtp-h265-04.txt




Abstract

   This memo describes an RTP payload format for the video coding
   standard ITU-T Recommendation H.265 and ISO/IEC International
   Standard 23008-2, both also known as High Efficiency Video Coding
   (HEVC) [HEVC] and developed by the Joint Collaborative Team on Video
   Coding (JCT-VC).  The RTP payload format allows for packetization of
   one or more Network Abstraction Layer (NAL) units in each RTP packet
   payload, as well as fragmentation of a NAL unit into multiple RTP
   packets.  Furthermore, it supports transmission of an HEVC bitstream
   over a single as well as multiple RTP streams.  The payload format
   has wide applicability in videoconferencing, Internet video
   streaming, and high bit-rate entertainment-quality video, among
   others.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that




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   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on November 28, 2014.

Copyright and License Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document.  Code Components extracted from this
   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.















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Table of Contents

   Abstract..........................................................1
   Status of this Memo...............................................1
   Table of Contents.................................................3
   1. Introduction...................................................5
      1.1. Overview of the HEVC Codec................................5
         1.1.1 Coding-Tool Features..................................5
         1.1.2 Systems and Transport Interfaces......................7
         1.1.3 Parallel Processing Support..........................14
         1.1.4 NAL Unit Header......................................16
      1.2. Overview of the Payload Format...........................17
   2. Conventions...................................................18
   3. Definitions and Abbreviations.................................18
      3.1 Definitions...............................................18
         3.1.1 Definitions from the HEVC Specification..............18
         3.1.2 Definitions Specific to This Memo....................20
      3.2 Abbreviations.............................................22
   4. RTP Payload Format............................................23
      4.1 RTP Header Usage..........................................23
      4.2 Payload Header Usage......................................26
      4.3 Payload Structures........................................26
      4.4 Transmission Modes........................................27
      4.5 Decoding Order Number.....................................28
      4.6 Single NAL Unit Packets...................................30
      4.7 Aggregation Packets (APs).................................31
      4.8 Fragmentation Units (FUs).................................35
      4.9 PACI packets..............................................38
         4.9.1 Reasons for the PACI rules (informative).............41
         4.9.2 PACI extensions (Informative)........................41
      4.10 Temporal Scalability Control Information.................43
   5. Packetization Rules...........................................45
   6. De-packetization Process......................................45
   7. Payload Format Parameters.....................................48
      7.1 Media Type Registration...................................48
      7.2 SDP Parameters............................................73
         7.2.1 Mapping of Payload Type Parameters to SDP............73
         7.2.2 Usage with SDP Offer/Answer Model....................74
         7.2.3 Usage in Declarative Session Descriptions............83


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         7.2.4 Parameter Sets Considerations........................84
         7.2.5 Dependency Signaling in Multi-Stream Mode............84
   8. Use with Feedback Messages....................................85
      8.1 Picture Loss Indication (PLI).............................86
      8.2 Slice Loss Indication.....................................86
      8.3 Use of HEVC with the RPSI Feedback Message................87
      8.4 Full Intra Request (FIR)..................................88
   9. Security Considerations.......................................88
   10. Congestion Control...........................................90
   11. IANA Consideration...........................................91
   12. Acknowledgements.............................................91
   13. References...................................................91
      13.1 Normative References.....................................91
      13.2 Informative References...................................93
   14. Authors' Addresses...........................................95































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1. Introduction

1.1. Overview of the HEVC Codec

   High Efficiency Video Coding [HEVC], formally known as ITU-T
   Recommendation H.265 and ISO/IEC International Standard 23008-2 was
   ratified by ITU-T in April 2013 and reportedly provides significant
   coding efficiency gains over H.264 [H.264].

   As both H.264 [H.264] and its RTP payload format [RFC6184] are
   widely deployed and generally known in the relevant implementer
   communities, frequently only the differences between those two
   specifications are highlighted in non-normative, explanatory parts
   of this memo.  Basic familiarity with both specifications is assumed
   for those parts.  However, the normative parts of this memo do not
   require study of H.264 or its RTP payload format.

   H.264 and HEVC share a similar hybrid video codec design.
   Conceptually, both technologies include a video coding layer (VCL),
   which is often used to refer to the coding-tool features, and a
   network abstraction layer (NAL), which is often used to refer to the
   systems and transport interface aspects of the codecs.

1.1.1 Coding-Tool Features

   Similarly to earlier hybrid-video-coding-based standards, including
   H.264, the following basic video coding design is employed by HEVC.
   A prediction signal is first formed either by intra or motion
   compensated prediction, and the residual (the difference between the
   original and the prediction) is then coded.  The gains in coding
   efficiency are achieved by redesigning and improving almost all
   parts of the codec over earlier designs.  In addition, HEVC includes
   several tools to make the implementation on parallel architectures
   easier.  Below is a summary of HEVC coding-tool features.

   Quad-tree block and transform structure

   One of the major tools that contribute significantly to the coding
   efficiency of HEVC is the usage of flexible coding blocks and
   transforms, which are defined in a hierarchical quad-tree manner.
   Unlike H.264, where the basic coding block is a macroblock of fixed



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   size 16x16, HEVC defines a Coding Tree Unit (CTU) of a maximum size
   of 64x64.  Each CTU can be divided into smaller units in a
   hierarchical quad-tree manner and can represent smaller blocks down
   to size 4x4.  Similarly, the transforms used in HEVC can have
   different sizes, starting from 4x4 and going up to 32x32.  Utilizing
   large blocks and transforms contribute to the major gain of HEVC,
   especially at high resolutions.

   Entropy coding

   HEVC uses a single entropy coding engine, which is based on Context
   Adaptive Binary Arithmetic Coding (CABAC), whereas H.264 uses two
   distinct entropy coding engines.  CABAC in HEVC shares many
   similarities with CABAC of H.264, but contains several improvements.
   Those include improvements in coding efficiency and lowered
   implementation complexity, especially for parallel architectures.

   In-loop filtering

   H.264 includes an in-loop adaptive deblocking filter, where the
   blocking artifacts around the transform edges in the reconstructed
   picture are smoothed to improve the picture quality and compression
   efficiency.  In HEVC, a similar deblocking filter is employed but
   with somewhat lower complexity.  In addition, pictures undergo a
   subsequent filtering operation called Sample Adaptive Offset (SAO),
   which is a new design element in HEVC.  SAO basically adds a pixel-
   level offset in an adaptive manner and usually acts as a de-ringing
   filter.  It is observed that SAO improves the picture quality,
   especially around sharp edges contributing substantially to visual
   quality improvements of HEVC.

   Motion prediction and coding

   There have been a number of improvements in this area that are
   summarized as follows.  The first category is motion merge and
   advanced motion vector prediction (AMVP) modes.  The motion
   information of a prediction block can be inferred from the spatially
   or temporally neighboring blocks.  This is similar to the DIRECT
   mode in H.264 but includes new aspects to incorporate the flexible
   quad-tree structure and methods to improve the parallel
   implementations.  In addition, the motion vector predictor can be


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   signaled for improved efficiency.  The second category is high-
   precision interpolation.  The interpolation filter length is
   increased to 8-tap from 6-tap, which improves the coding efficiency
   but also comes with increased complexity.  In addition, the
   interpolation filter is defined with higher precision without any
   intermediate rounding operations to further improve the coding
   efficiency.

   Intra prediction and intra coding

   Compared to 8 intra prediction modes in H.264, HEVC supports angular
   intra prediction with 33 directions.  This increased flexibility
   improves both objective coding efficiency and visual quality as the
   edges can be better predicted and ringing artifacts around the edges
   can be reduced.  In addition, the reference samples are adaptively
   smoothed based on the prediction direction.  To avoid contouring
   artifacts a new interpolative prediction generation is included to
   improve the visual quality.  Furthermore, discrete sine transform
   (DST) is utilized instead of traditional discrete cosine transform
   (DCT) for 4x4 intra transform blocks.

   Other coding-tool features

   HEVC includes some tools for lossless coding and efficient screen
   content coding, such as skipping the transform for certain blocks.
   These tools are particularly useful for example when streaming the
   user-interface of a mobile device to a large display.

1.1.2 Systems and Transport Interfaces

   HEVC inherited the basic systems and transport interfaces designs,
   such as the NAL-unit-based syntax structure, the hierarchical syntax
   and data unit structure from sequence-level parameter sets, multi-
   picture-level or picture-level parameter sets, slice-level header
   parameters, lower-level parameters, the supplemental enhancement
   information (SEI) message mechanism, the hypothetical reference
   decoder (HRD) based video buffering model, and so on.  In the
   following, a list of differences in these aspects compared to H.264
   is summarized.





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   Video parameter set

   A new type of parameter set, called video parameter set (VPS), was
   introduced.  For the first (2013) version of [HEVC], the video
   parameter set NAL unit is required to be available prior to its
   activation, while the information contained in the video parameter
   set is not necessary for operation of the decoding process.  For
   future HEVC extensions, such as the 3D or scalable extensions, the
   video parameter set is expected to include information necessary for
   operation of the decoding process, e.g. decoding dependency or
   information for reference picture set construction of enhancement
   layers.  The VPS provides a "big picture" of a bitstream, including
   what types of operation points are provided, the profile, tier, and
   level of the operation points, and some other high-level properties
   of the bitstream that can be used as the basis for session
   negotiation and content selection, etc. (see section 7.1).

   Profile, tier and level

   The profile, tier and level syntax structure that can be included in
   both VPS and sequence parameter set (SPS) includes 12 bytes of data
   to describe the entire bitstream (including all temporally scalable
   layers, which are referred to as sub-layers in the HEVC
   specification), and can optionally include more profile, tier and
   level information pertaining to individual temporally scalable
   layers.  The profile indicator indicates the "best viewed as"
   profile when the bitstream conforms to multiple profiles, similar to
   the major brand concept in the ISO base media file format (ISOBMFF)
   [ISOBMFF] and file formats derived based on ISOBMFF, such as the
   3GPP file format [3GP].  The profile, tier and level syntax
   structure also includes the indications of whether the bitstream is
   free of frame-packed content, whether the bitstream is free of
   interlaced source content and free of field pictures, i.e. contains
   only frame pictures of progressive source, such that clients/players
   with no support of post-processing functionalities for handling of
   frame-packed or interlaced source content or field pictures can
   reject those bitstreams.







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   Bitstream and elementary stream

   HEVC includes a definition of an elementary stream, which is new
   compared to H.264.  An elementary stream consists of a sequence of
   one or more bitstreams.  An elementary stream that consists of two
   or more bitstreams has typically been formed by splicing together
   two or more bitstreams (or parts thereof).  When an elementary
   stream contains more than one bitstream, the last NAL unit of the
   last access unit of a bitstream (except the last bitstream in the
   elementary stream) must contain an end of bitstream NAL unit and the
   first access unit of the subsequent bitstream must be an intra
   random access point (IRAP) access unit.  This IRAP access unit may
   be a clean random access (CRA), broken link access (BLA), or
   instantaneous decoding refresh (IDR) access unit.

   Random access support

   HEVC includes signaling in NAL unit header, through NAL unit types,
   of IRAP pictures beyond IDR pictures.  Three types of IRAP pictures,
   namely IDR, CRA and BLA pictures are supported, wherein IDR pictures
   are conventionally referred to as closed group-of-pictures (closed-
   GOP) random access points, and CRA and BLA pictures are those
   conventionally referred to as open-GOP random access points.  BLA
   pictures usually originate from splicing of two bitstreams or part
   thereof at a CRA picture, e.g. during stream switching.  To enable
   better systems usage of IRAP pictures, altogether six different NAL
   units are defined to signal the properties of the IRAP pictures,
   which can be used to better match the stream access point (SAP)
   types as defined in the ISOBMFF [ISOBMFF], which are utilized for
   random access support in both 3GP-DASH [3GPDASH] and MPEG DASH
   [MPEGDASH].  Pictures following an IRAP picture in decoding order
   and preceding the IRAP picture in output order are referred to as
   leading pictures associated with the IRAP picture.  There are two
   types of leading pictures, namely random access decodable leading
   (RADL) pictures and random access skipped leading (RASL) pictures.
   RADL pictures are decodable when the decoding started at the
   associated IRAP picture, and RASL pictures are not decodable when
   the decoding started at the associated IRAP picture and are usually
   discarded.  HEVC provides mechanisms to enable the specification of
   conformance of bitstreams with RASL pictures being discarded, thus



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   to provide a standard-compliant way to enable systems components to
   discard RASL pictures when needed.

   Temporal scalability support

   HEVC includes an improved support of temporal scalability, by
   inclusion of the signaling of TemporalId in the NAL unit header, the
   restriction that pictures of a particular temporal sub-layer cannot
   be used for inter prediction reference by pictures of a lower
   temporal sub-layer, the sub-bitstream extraction process, and the
   requirement that each sub-bitstream extraction output be a
   conforming bitstream.  Media-aware network elements (MANEs) can
   utilize the TemporalId in the NAL unit header for stream adaptation
   purposes based on temporal scalability.

   Temporal sub-layer switching support

   HEVC specifies, through NAL unit types present in the NAL unit
   header, the signaling of temporal sub-layer access (TSA) and
   stepwise temporal sub-layer access (STSA).  A TSA picture and
   pictures following the TSA picture in decoding order do not use
   pictures prior to the TSA picture in decoding order with TemporalId
   greater than or equal to that of the TSA picture for inter
   prediction reference.  A TSA picture enables up-switching, at the
   TSA picture, to the sub-layer containing the TSA picture or any
   higher sub-layer, from the immediately lower sub-layer.  An STSA
   picture does not use pictures with the same TemporalId as the STSA
   picture for inter prediction reference.  Pictures following an STSA
   picture in decoding order with the same TemporalId as the STSA
   picture do not use pictures prior to the STSA picture in decoding
   order with the same TemporalId as the STSA picture for inter
   prediction reference.  An STSA picture enables up-switching, at the
   STSA picture, to the sub-layer containing the STSA picture, from the
   immediately lower sub-layer.

   Sub-layer reference or non-reference pictures

   The concept and signaling of reference/non-reference pictures in
   HEVC are different from H.264.  In H.264, if a picture may be used
   by any other picture for inter prediction reference, it is a
   reference picture; otherwise it is a non-reference picture, and this


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   is signaled by two bits in the NAL unit header.  In HEVC, a picture
   is called a reference picture only when it is marked as "used for
   reference".  In addition, the concept of sub-layer reference picture
   was introduced.  If a picture may be used by another other picture
   with the same TemporalId for inter prediction reference, it is a
   sub-layer reference picture; otherwise it is a sub-layer non-
   reference picture.  Whether a picture is a sub-layer reference
   picture or sub-layer non-reference picture is signaled through NAL
   unit type values.

   Extensibility

   Besides the TemporalId in the NAL unit header, HEVC also includes
   the signaling of a six-bit layer ID in the NAL unit header, which
   must be equal to 0 for a single-layer bitstream.  Extension
   mechanisms have been included in VPS, SPS, PPS, SEI NAL unit, slice
   headers, and so on.  All these extension mechanisms enable future
   extensions in a backward compatible manner, such that bitstreams
   encoded according to potential future HEVC extensions can be fed to
   then-legacy decoders (e.g. HEVC version 1 decoders) and the then-
   legacy decoders can decode and output the base layer bitstream.

   Bitstream extraction

   HEVC includes a bitstream extraction process as an integral part of
   the overall decoding process, as well as specification of the use of
   the bitstream extraction process in description of bitstream
   conformance tests as part of the hypothetical reference decoder
   (HRD) specification.

   Reference picture management

   The reference picture management of HEVC, including reference
   picture marking and removal from the decoded picture buffer (DPB) as
   well as reference picture list construction (RPLC), differs from
   that of H.264.  Instead of the sliding window plus adaptive memory
   management control operation (MMCO) based reference picture marking
   mechanism in H.264, HEVC specifies a reference picture set (RPS)
   based reference picture management and marking mechanism, and the
   RPLC is consequently based on the RPS mechanism.  A reference
   picture set consists of a set of reference pictures associated with


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   a picture, consisting of all reference pictures that are prior to
   the associated picture in decoding order, that may be used for inter
   prediction of the associated picture or any picture following the
   associated picture in decoding order.  The reference picture set
   consists of five lists of reference pictures; RefPicSetStCurrBefore,
   RefPicSetStCurrAfter, RefPicSetStFoll, RefPicSetLtCurr and
   RefPicSetLtFoll.  RefPicSetStCurrBefore, RefPicSetStCurrAfter and
   RefPicSetLtCurr contain all reference pictures that may be used in
   inter prediction of the current picture and that may be used in
   inter prediction of one or more of the pictures following the
   current picture in decoding order.  RefPicSetStFoll and
   RefPicSetLtFoll consist of all reference pictures that are not used
   in inter prediction of the current picture but may be used in inter
   prediction of one or more of the pictures following the current
   picture in decoding order.  RPS provides an "intra-coded" signaling
   of the DPB status, instead of an "inter-coded" signaling, mainly for
   improved error resilience.  The RPLC process in HEVC is based on the
   RPS, by signaling an index to an RPS subset for each reference
   index.  The RPLC process has been simplified compared to that in
   H.264, by removal of the reference picture list modification (also
   referred to as reference picture list reordering) process.

   Ultra low delay support

   HEVC specifies a sub-picture-level HRD operation, for support of the
   so-called ultra-low delay.  The mechanism specifies a standard-
   compliant way to enable delay reduction below one picture interval.
   Sub-picture-level coded picture buffer (CPB) and DPB parameters may
   be signaled, and utilization of these information for the derivation
   of CPB timing (wherein the CPB removal time corresponds to decoding
   time) and DPB output timing (display time) is specified.  Decoders
   are allowed to operate the HRD at the conventional access-unit-
   level, even when the sub-picture-level HRD parameters are present.

   New SEI messages

   HEVC inherits many H.264 SEI messages with changes in syntax and/or
   semantics making them applicable to HEVC.  Additionally, there are a
   few new SEI messages reviewed briefly in the following paragraphs.




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   The display orientation SEI message informs the decoder of a
   transformation that is recommended to be applied to the cropped
   decoded picture prior to display, such that the pictures can be
   properly displayed, e.g. in an upside-up manner.

   The structure of pictures SEI message provides information on the
   NAL unit types, picture order count values, and prediction
   dependencies of a sequence of pictures.  The SEI message can be used
   for example for concluding what impact a lost picture has on other
   pictures.

   The decoded picture hash SEI message provides a checksum derived
   from the sample values of a decoded picture.  It can be used for
   detecting whether a picture was correctly received and decoded.

   The active parameter sets SEI message includes the IDs of the active
   video parameter set and the active sequence parameter set and can be
   used to activate VPSs and SPSs.  In addition, the SEI message
   includes the following indications: 1) An indication of whether
   "full random accessibility" is supported (when supported, all
   parameter sets needed for decoding of the remaining of the bitstream
   when random accessing from the beginning of the current coded video
   sequence by completely discarding all access units earlier in
   decoding order are present in the remaining bitstream and all coded
   pictures in the remaining bitstream can be correctly decoded); 2) An
   indication of whether there is no parameter set within the current
   coded video sequence that updates another parameter set of the same
   type preceding in decoding order.  An update of a parameter set
   refers to the use of the same parameter set ID but with some other
   parameters changed.  If this property is true for all coded video
   sequences in the bitstream, then all parameter sets can be sent out-
   of-band before session start.

   The decoding unit information SEI message provides coded picture
   buffer removal delay information for a decoding unit.  The message
   can be used in very-low-delay buffering operations.

   The region refresh information SEI message can be used together with
   the recovery point SEI message (present in both H.264 and HEVC) for
   improved support of gradual decoding refresh (GDR).  This supports
   random access from inter-coded pictures, wherein complete pictures


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   can be correctly decoded or recovered after an indicated number of
   pictures in output/display order.

1.1.3 Parallel Processing Support

   The reportedly significantly higher encoding computational demand of
   HEVC over H.264, in conjunction with the ever increasing video
   resolution (both spatially and temporally) required by the market,
   led to the adoption of VCL coding tools specifically targeted to
   allow for parallelization on the sub-picture level.  That is,
   parallelization occurs, at the minimum, at the granularity of an
   integer number of CTUs.  The targets for this type of high-level
   parallelization are multicore CPUs and DSPs as well as
   multiprocessor systems.  In a system design, to be useful, these
   tools require signaling support, which is provided in Section 7 of
   this memo.  This section provides a brief overview of the tools
   available in [HEVC].

   Many of the tools incorporated in HEVC were designed keeping in mind
   the potential parallel implementations in multi-core/multi-processor
   architectures.  Specifically, for parallelization, four picture
   partition strategies are available.

   Slices are segments of the bitstream that can be reconstructed
   independently from other slices within the same picture (though
   there may still be interdependencies through loop filtering
   operations).  Slices are the only tool that can be used for
   parallelization that is also available, in virtually identical form,
   in H.264.  Slices based parallelization does not require much inter-
   processor or inter-core communication (except for inter-processor or
   inter-core data sharing for motion compensation when decoding a
   predictively coded picture, which is typically much heavier than
   inter-processor or inter-core data sharing due to in-picture
   prediction), as slices are designed to be independently decodable.
   However, for the same reason, slices can require some coding
   overhead.  Further, slices (in contrast to some of the other tools
   mentioned below) also serve as the key mechanism for bitstream
   partitioning to match Maximum Transfer Unit (MTU) size requirements,
   due to the in-picture independence of slices and the fact that each
   regular slice is encapsulated in its own NAL unit.  In many cases,
   the goal of parallelization and the goal of MTU size matching can


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   place contradicting demands to the slice layout in a picture.  The
   realization of this situation led to the development of the more
   advanced tools mentioned below.

   Dependent slice segments allow for fragmentation of a coded slice
   into fragments at CTU boundaries without breaking any in-picture
   prediction mechanism.  They are complementary to the fragmentation
   mechanism described in this memo in that they need the cooperation
   of the encoder.  As a dependent slice segment necessarily contains
   an integer number of CTUs, a decoder using multiple cores operating
   on CTUs can process a dependent slice segment without communicating
   parts of the slice segment's bitstream to other cores.
   Fragmentation, as specified in this memo, in contrast, does not
   guarantee that a fragment contains an integer number of CTUs.

   In wavefront parallel processing (WPP), the picture is partitioned
   into rows of CTUs.  Entropy decoding and prediction are allowed to
   use data from CTUs in other partitions.  Parallel processing is
   possible through parallel decoding of CTU rows, where the start of
   the decoding of a row is delayed by two CTUs, so to ensure that data
   related to a CTU above and to the right of the subject CTU is
   available before the subject CTU is being decoded.  Using this
   staggered start (which appears like a wavefront when represented
   graphically), parallelization is possible with up to as many
   processors/cores as the picture contains CTU rows.

   Because in-picture prediction between neighboring CTU rows within a
   picture is allowed, the required inter-processor/inter-core
   communication to enable in-picture prediction can be substantial.
   The WPP partitioning does not result in the creation of more NAL
   units compared to when it is not applied, thus WPP cannot be used
   for MTU size matching, though slices can be used in combination for
   that purpose.

   Tiles define horizontal and vertical boundaries that partition a
   picture into tile columns and rows.  The scan order of CTUs is
   changed to be local within a tile (in the order of a CTU raster scan
   of a tile), before decoding the top-left CTU of the next tile in the
   order of tile raster scan of a picture.  Similar to slices, tiles
   break in-picture prediction dependencies (including entropy decoding
   dependencies).  However, they do not need to be included into


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   individual NAL units (same as WPP in this regard), hence tiles
   cannot be used for MTU size matching, though slices can be used in
   combination for that purpose.  Each tile can be processed by one
   processor/core, and the inter-processor/inter-core communication
   required for in-picture prediction between processing units decoding
   neighboring tiles is limited to conveying the shared slice header in
   cases a slice is spanning more than one tile, and loop filtering
   related sharing of reconstructed samples and metadata.  Insofar,
   tiles are less demanding in terms of inter-processor communication
   bandwidth compared to WPP due to the in-picture independence between
   two neighboring partitions.

1.1.4 NAL Unit Header

   HEVC maintains the NAL unit concept of H.264 with modifications.
   HEVC uses a two-byte NAL unit header, as shown in Figure 1.  The
   payload of a NAL unit refers to the NAL unit excluding the NAL unit
   header.

                     +---------------+---------------+
                     |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |F|   Type    |  LayerId  | TID |
                     +-------------+-----------------+

              Figure 1 The structure of HEVC NAL unit header

   The semantics of the fields in the NAL unit header are as specified
   in [HEVC] and described briefly below for convenience.  In addition
   to the name and size of each field, the corresponding syntax element
   name in [HEVC] is also provided.

   F: 1 bit
      forbidden_zero_bit.  MUST be zero.  HEVC declares a value of 1 as
      a syntax violation.  Note that the inclusion of this bit in the
      NAL unit header is to enable transport of HEVC video over MPEG-2
      transport systems (avoidance of start code emulations) [MPEG2S].

   Type: 6 bits




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      nal_unit_type.  This field specifies the NAL unit type as defined
      in Table 7-1 of [HEVC].  If the most significant bit of this
      field of a NAL unit is equal to 0 (i.e. the value of this field
      is less than 32), the NAL unit is a VCL NAL unit.  Otherwise, the
      NAL unit is a non-VCL NAL unit.  For a reference of all currently
      defined NAL unit types and their semantics, please refer to
      Section 7.4.1 in [HEVC].

   LayerId: 6 bits
      nuh_layer_id.  MUST be equal to zero.  It is anticipated that in
      future scalable or 3D video coding extensions of this
      specification, this syntax element will be used to identify
      additional layers that may be present in the coded video
      sequence, wherein a layer may be, e.g. a spatial scalable layer,
      a quality scalable layer, a texture view, or a depth view.

   TID: 3 bits
      nuh_temporal_id_plus1.  This field specifies the temporal
      identifier of the NAL unit plus 1.  The value of TemporalId is
      equal to TID minus 1.  A TID value of 0 is illegal to ensure that
      there is at least one bit in the NAL unit header equal to 1, so
      to enable independent considerations of start code emulations in
      the NAL unit header and in the NAL unit payload data.

1.2. Overview of the Payload Format

   This payload format defines the following processes required for
   transport of HEVC coded data over RTP [RFC3550]:

   o Usage of RTP header with this payload format

   o Packetization of HEVC coded NAL units into RTP packets using three
     types of payload structures, namely single NAL unit packet,
     aggregation packet, and fragment unit

   o Transmission of HEVC NAL units of the same bitstream within a
     single RTP stream or multiple RTP streams within one or more RTP
     sessions, where within an RTP stream transmission of NAL units may
     be either non-interleaved (i.e. the transmission order of NAL
     units is the same as their decoding order) or interleaved (i.e.



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     the transmission order of NAL units is different from their
     decoding order)

   o Media type parameters to be used with the Session Description
     Protocol (SDP) [RFC4566]

   o A payload header extension mechanism and data structures for
     enhanced support of temporal scalability based on that extension
     mechanism.

2. Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119].

   In this document, these key words will appear with that
   interpretation only when in ALL CAPS.  Lower case uses of these
   words are not to be interpreted as carrying the RFC 2119
   significance.

   This specification uses the notion of setting and clearing a bit
   when bit fields are handled.  Setting a bit is the same as assigning
   that bit the value of 1 (On).  Clearing a bit is the same as
   assigning that bit the value of 0 (Off).

3. Definitions and Abbreviations

3.1 Definitions

   This document uses the terms and definitions of [HEVC].  Section
   3.1.1 lists relevant definitions copied from [HEVC] for convenience.
   Section 3.1.2 provides definitions specific to this memo.

3.1.1 Definitions from the HEVC Specification

   access unit: A set of NAL units that are associated with each other
   according to a specified classification rule, are consecutive in
   decoding order, and contain exactly one coded picture.




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   BLA access unit: An access unit in which the coded picture is a BLA
   picture.

   BLA picture: An IRAP picture for which each VCL NAL unit has
   nal_unit_type equal to BLA_W_LP, BLA_W_RADL, or BLA_N_LP.

   coded video sequence: A sequence of access units that consists, in
   decoding order, of an IRAP access unit with NoRaslOutputFlag equal
   to 1, followed by zero or more access units that are not IRAP access
   units with NoRaslOutputFlag equal to 1, including all subsequent
   access units up to but not including any subsequent access unit that
   is an IRAP access unit with NoRaslOutputFlag equal to 1.

      Informative note: An IRAP access unit may be an IDR access unit,
      a BLA access unit, or a CRA access unit.  The value of
      NoRaslOutputFlag is equal to 1 for each IDR access unit, each BLA
      access unit, and each CRA access unit that is the first access
      unit in the bitstream in decoding order, is the first access unit
      that follows an end of sequence NAL unit in decoding order, or
      has HandleCraAsBlaFlag equal to 1.

   CRA access unit: An access unit in which the coded picture is a CRA
   picture.

   CRA picture: A RAP picture for which each VCL NAL unit has
   nal_unit_type equal to CRA_NUT.

   IDR access unit: An access unit in which the coded picture is an IDR
   picture.

   IDR picture: A RAP picture for which each VCL NAL unit has
   nal_unit_type equal to IDR_W_RADL or IDR_N_LP.

   IRAP access unit: An access unit in which the coded picture is an
   IRAP picture.

   IRAP picture: A coded picture for which each VCL NAL unit has
   nal_unit_type in the range of BLA_W_LP (16) to RSV_IRAP_VCL23 (23),
   inclusive.





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   layer: A set of VCL NAL units that all have a particular value of
   nuh_layer_id and the associated non-VCL NAL units, or one of a set
   of syntactical structures having a hierarchical relationship.

   operation point: bitstream created from another bitstream by
   operation of the sub-bitstream extraction process with the another
   bitstream, a target highest TemporalId, and a target layer
   identifier list as inputs.

   random access: The act of starting the decoding process for a
   bitstream at a point other than the beginning of the bitstream.

   sub-layer: A temporal scalable layer of a temporal scalable
   bitstream consisting of VCL NAL units with a particular value of the
   TemporalId variable, and the associated non-VCL NAL units.

   sub-layer representation: A subset of the bitstream consisting of
   NAL units of a particular sub-layer and the lower sub-layers.

   tile: A rectangular region of coding tree blocks within a particular
   tile column and a particular tile row in a picture.

   tile column: A rectangular region of coding tree blocks having a
   height equal to the height of the picture and a width specified by
   syntax elements in the picture parameter set.

   tile row: A rectangular region of coding tree blocks having a height
   specified by syntax elements in the picture parameter set and a
   width equal to the width of the picture.

3.1.2 Definitions Specific to This Memo

   dependee RTP stream: An RTP stream on which another RTP stream
   depends.  All RTP streams in an MSM except for the highest RTP
   stream are dependee RTP streams.

   highest RTP stream: The RTP stream on which no other RTP stream
   depends.  The RTP stream in an SSM is the highest RTP stream.

   media aware network element (MANE): A network element, such as a
   middlebox, selective forwarding unit, or application layer gateway



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   that is capable of parsing certain aspects of the RTP payload
   headers or the RTP payload and reacting to their contents.

      Informative note: The concept of a MANE goes beyond normal
      routers or gateways in that a MANE has to be aware of the
      signaling (e.g. to learn about the payload type mappings of the
      media streams), and in that it has to be trusted when working
      with SRTP.  The advantage of using MANEs is that they allow
      packets to be dropped according to the needs of the media coding.
      For example, if a MANE has to drop packets due to congestion on a
      certain link, it can identify and remove those packets whose
      elimination produces the least adverse effect on the user
      experience.  After dropping packets, MANEs must rewrite RTCP
      packets to match the changes to the RTP stream as specified in
      Section 7 of [RFC3550].

   multi-stream mode(MSM): Transmission of an HEVC bitstream using more
   than one RTP stream.

   NAL unit decoding order: A NAL unit order that conforms to the
   constraints on NAL unit order given in Section 7.4.2.4 in [HEVC].

   NAL-unit-like structure: A data structure that is similar to NAL
   units in the sense that it also has a NAL unit header and a payload,
   with a difference that the payload does not follow the start code
   emulation prevention mechanism required for the NAL unit syntax as
   specified in Section 7.3.1.1 of [HEVC].  Examples NAL-unit-like
   structures defined in this memo are packet payloads of AP, PACI, and
   FU packets.

   NALU-time: The value that the RTP timestamp would have if the NAL
   unit would be transported in its own RTP packet.

   RTP stream: See [I-D.ietf-avtext-rtp-grouping-taxonomy].  Within the
   scope of this memo, one RTP stream is utilized to transport one or
   more temporal sub-layers.

   single-stream mode (SSM): Transmission of an HEVC bitstream using
   only one RTP stream.





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   transmission order: The order of packets in ascending RTP sequence
   number order (in modulo arithmetic).  Within an aggregation packet,
   the NAL unit transmission order is the same as the order of
   appearance of NAL units in the packet.

3.2 Abbreviations

   AP       Aggregation Packet

   BLA      Broken Link Access

   CRA      Clean Random Access

   CTB      Coding Tree Block

   CTU      Coding Tree Unit

   CVS      Coded Video Sequence

   DPH      Decoded Picture Hash

   FU       Fragmentation Unit

   GDR      Gradual Decoding Refresh

   HRD      Hypothetical Reference Decoder

   IDR      Instantaneous Decoding Refresh

   IRAP     Intra Random Access Point

   MANE     Media Aware Network Element

   MSM      Multi-Stream Mode

   MTU      Maximum Transfer Unit

   NAL      Network Abstraction Layer

   NALU     Network Abstraction Layer Unit

   PACI     PAyload Content Information



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   PHES     Payload Header Extension Structure

   PPS      Picture Parameter Set

   RADL     Random Access Decodable Leading (Picture)

   RASL     Random Access Skipped Leading (Picture)

   RPS      Reference Picture Set

   SEI      Supplemental Enhancement Information

   SPS      Sequence Parameter Set

   SSM      Single-Stream Mode

   STSA     Step-wise Temporal Sub-layer Access

   TSA      Temporal Sub-layer Access

   TCSI     Temporal Scalability Control Information

   VCL      Video Coding Layer

   VPS      Video Parameter Set

4. RTP Payload Format

4.1 RTP Header Usage

   The format of the RTP header is specified in [RFC3550] and reprinted
   in Figure 2 for convenience.  This payload format uses the fields of
   the header in a manner consistent with that specification.

   The RTP payload (and the settings for some RTP header bits) for
   aggregation packets and fragmentation units are specified in
   Sections 4.7 and 4.8, respectively.








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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V=2|P|X|  CC   |M|     PT      |       sequence number         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           timestamp                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           synchronization source (SSRC) identifier            |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |            contributing source (CSRC) identifiers             |
   |                             ....                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2 RTP header according to [RFC3550]

   The RTP header information to be set according to this RTP payload
   format is set as follows:

   Marker bit (M): 1 bit

      Set for the last packet, carried in the current RTP stream, of
      the access unit, in line with the normal use of the M bit in
      video formats, to allow an efficient playout buffer handling.
      When MSM is in use, if an access unit appears in multiple RTP
      streams, the marker bit is set on each RTP stream's last packet
      of the access unit.

         Informative note: The content of a NAL unit does not tell
         whether or not the NAL unit is the last NAL unit, in decoding
         order, of an access unit.  An RTP sender implementation may
         obtain this information from the video encoder.  If, however,
         the implementation cannot obtain this information directly
         from the encoder, e.g. when the bitstream was pre-encoded, and
         also there is no timestamp allocated for each NAL unit, then
         the sender implementation can inspect subsequent NAL units in
         decoding order to determine whether or not the NAL unit is the
         last NAL unit of an access unit as follows.  A NAL unit naluX
         is the last NAL unit of an access unit if it is the last NAL
         unit of the bitstream or the next VCL NAL unit naluY in
         decoding order has the high-order bit of the first byte after
         its NAL unit header equal to 1, and all NAL units between


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         naluX and naluY, when present, have nal_unit_type in the range
         of 32 to 35, inclusive, equal to 39, or in the ranges of 41 to
         44, inclusive, or 48 to 55, inclusive.

   Payload type (PT): 7 bits

      The assignment of an RTP payload type for this new packet format
      is outside the scope of this document and will not be specified
      here.  The assignment of a payload type has to be performed
      either through the profile used or in a dynamic way.

         Informative note: It is not required to use different payload
         type values for different RTP streams in MSM.

   Sequence number (SN): 16 bits

      Set and used in accordance with RFC 3550.

   Timestamp: 32 bits

      The RTP timestamp is set to the sampling timestamp of the
      content.  A 90 kHz clock rate MUST be used.

      If the NAL unit has no timing properties of its own (e.g.
      parameter set and SEI NAL units), the RTP timestamp MUST be set
      to the RTP timestamp of the coded picture of the access unit in
      which the NAL unit (according to Section 7.4.2.4.4 of [HEVC]) is
      included.

      Receivers MUST use the RTP timestamp for the display process,
      even when the bitstream contains picture timing SEI messages or
      decoding unit information SEI messages as specified in [HEVC].
      However, this does not mean that picture timing SEI messages in
      the bitstream should be discarded, as picture timing SEI messages
      may contain frame-field information that is important in
      appropriately rendering interlaced video.

   Synchronization source (SSRC): 32-bits

      Used to identify the source of the RTP packets.  In SSM, by
      definition a single SSRC is used for all parts of a single
      bitstream.  In MSM, each SSRC is used for an RTP stream


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      containing a subset of the sub-layers for a single (temporally
      scalable) bitstream.  A receiver is required to correctly
      associate the set of SSRCs that are included parts of the same
      bitstream.

         Informative note: The term "bitstream" in this document is
         equivalent to the term "encoded stream" in [I-D.ietf-avtext-
         rtp-grouping-taxonomy].

4.2 Payload Header Usage

   The TID value indicates (among other things) the relative importance
   of an RTP packet, for example because NAL units belonging to higher
   temporal sub-layers are not used for the decoding of lower temporal
   sub-layers.  A lower value of TID indicates a higher importance.
   More important NAL units MAY be better protected against
   transmission losses than less important NAL units.

4.3 Payload Structures

   The first two bytes of the payload of an RTP packet are referred to
   as the payload header.  The payload header consists of the same
   fields (F, Type, LayerId, and TID) as the NAL unit header as shown
   in section 1.1.4, irrespective of the type of the payload structure.

   Four different types of RTP packet payload structures are specified.
   A receiver can identify the type of an RTP packet payload through
   the Type field in the payload header.

   The four different payload structures are as follows:

   o  Single NAL unit packet: Contains a single NAL unit in the
      payload, and the NAL unit header of the NAL unit also serves as
      the payload header.  This payload structure is specified in
      section 4.6.

   o  Aggregation packet (AP): Contains more than one NAL unit within
      one access unit.  This payload structure is specified in
      section 4.7.





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   o  Fragmentation unit (FU): Contains a subset of a single NAL unit.
      This payload structure is specified in section 4.8.

   o  PACI carrying RTP packet: Contains a payload header (that differs
      from other payload headers for efficiency), a Payload Header
      Extension Structure (PHES), and a PACI payload.  This payload
      structure is specified in section 4.9.

4.4 Transmission Modes

   This memo enables transmission of an HEVC bitstream over a single
   RTP stream or multiple RTP streams.  The concept and working
   principle is inherited from the design of what was called single and
   multiple session transmission in [RFC6190] and follows a similar
   design.  If only one RTP stream is used for transmission of the HEVC
   bitstream, the transmission mode is referred to as single-stream
   mode (SSM); otherwise (more than one RTP stream is used for
   transmission of the HEVC bitstream), the transmission mode is
   referred to as multi-stream mode (MSM).

   Dependency of one RTP stream on another RTP stream is typically
   indicated as specified in [RFC5583].  When an RTP stream A depends
   on another RTP stream B, the RTP stream B is referred to as a
   dependee RTP stream of the RTP stream A.

      Informative note: An MSM may involve one or more RTP sessions.
      For example, each RTP stream in an MSM may be in its own RTP
      session.  For another example, a set of multiple RTP streams in
      an MSM may belong to the same RTP session, e.g. as indicated by
      the mechanism specified in [I-D.ietf-avtcore-rtp-multi-stream] or
      [I-D.ietf-mmusic-sdp-bundle-negotiation].

   SSM SHOULD be used for point-to-point unicast scenarios, while MSM
   SHOULD be used for point-to-multipoint multicast scenarios where
   different receivers require different operation points of the same
   HEVC bitstream, to improve bandwidth utilizing efficiency.

      Informative note: A multicast may degrade to a unicast after all
      but one receivers have left (this is a justification of the first
      "SHOULD" instead of "MUST"), and there might be scenarios where
      MSM is desirable but not possible e.g. when IP multicast is not



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      deployed in certain network (this is a justification of the
      second "SHOULD" instead of "MUST").

   The transmission mode is indicated by the tx-mode media parameter
   (see section 7.1).  If tx-mode is equal to "SSM", SSM MUST be used.
   Otherwise (tx-mode is equal to "MSM"), MSM MUST be used.

   Receivers MUST support both SSM and MSM.

4.5 Decoding Order Number

   For each NAL unit, the variable AbsDon is derived, representing the
   decoding order number that is indicative of the NAL unit decoding
   order.

   Let NAL unit n be the n-th NAL unit in transmission order within an
   RTP stream.

   If tx-mode is equal to "SSM" and sprop-max-don-diff is equal to 0,
   AbsDon[n], the value of AbsDon for NAL unit n, is derived as equal
   to n.

   Otherwise (tx-mode is equal to "MSM" or sprop-max-don-diff is
   greater than 0), AbsDon[n] is derived as follows, where DON[n] is
   the value of the variable DON for NAL unit n:

   o  If n is equal to 0 (i.e. NAL unit n is the very first NAL unit in
      transmission order), AbsDon[0] is set equal to DON[0].

   o  Otherwise (n is greater than 0), the following applies for
      derivation of AbsDon[n]:

            If DON[n] == DON[n-1],
                AbsDon[n] = AbsDon[n-1]

            If (DON[n] > DON[n-1] and DON[n] - DON[n-1] < 32768),
                AbsDon[n] = AbsDon[n-1] + DON[n] - DON[n-1]

            If (DON[n] < DON[n-1] and DON[n-1] - DON[n] >= 32768),
                AbsDon[n] = AbsDon[n-1] + 65536 - DON[n-1] + DON[n]




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            If (DON[n] > DON[n-1] and DON[n] - DON[n-1] >= 32768),
                AbsDon[n] = AbsDon[n-1] - (DON[n-1] + 65536 - DON[n])

            If (DON[n] < DON[n-1] and DON[n-1] - DON[n] < 32768),
                AbsDon[n] = AbsDon[n-1] - (DON[n-1] - DON[n])

   For any two NAL units m and n, the following applies:

   o  AbsDon[n] greater than AbsDon[m] indicates that NAL unit n
      follows NAL unit m in NAL unit decoding order.

   o  When AbsDon[n] is equal to AbsDon[m], the NAL unit decoding order
      of the two NAL units can be in either order.

   o  AbsDon[n] less than AbsDon[m] indicates that NAL unit n precedes
      NAL unit m in decoding order.

   When two consecutive NAL units in the NAL unit decoding order have
   different values of AbsDon, the value of AbsDon for the second NAL
   unit in decoding order MUST be greater than the value of AbsDon for
   the first NAL unit, and the absolute difference between the two
   AbsDon values MAY be greater than or equal to 1.

      Informative note: There are multiple reasons to allow for the
      absolute difference of the values of AbsDon for two consecutive
      NAL units in the NAL unit decoding order to be greater than one.
      An increment by one is not required, as at the time of
      associating values of AbsDon to NAL units, it may not be known
      whether all NAL units are to be delivered to the receiver.  For
      example, a gateway may not forward VCL NAL units of higher sub-
      layers or some SEI NAL units when there is congestion in the
      network.  In another example, the first intra-coded picture of a
      pre-encoded clip is transmitted in advance to ensure that it is
      readily available in the receiver, and when transmitting the
      first intra-coded picture, the originator does not exactly know
      how many NAL units will be encoded before the first intra-coded
      picture of the pre-encoded clip follows in decoding order.  Thus,
      the values of AbsDon for the NAL units of the first intra-coded
      picture of the pre-encoded clip have to be estimated when they
      are transmitted, and gaps in values of AbsDon may occur.  Another




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      example is MSM where the AbsDon values must indicate cross-layer
      decoding order for NAL units conveyed in all the RTP streams.

4.6 Single NAL Unit Packets

   A single NAL unit packet contains exactly one NAL unit, and consists
   of a payload header (denoted as PayloadHdr), a conditional 16-bit
   DONL field (in network byte order), and the NAL unit payload data
   (the NAL unit excluding its NAL unit header) of the contained NAL
   unit, as shown in Figure 3.

   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           PayloadHdr          |      DONL (conditional)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                  NAL unit payload data                        |
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 3 The structure a single NAL unit packet

   The payload header SHOULD be an exact copy of the NAL unit header of
   the contained NAL unit.  However, the Type (i.e. nal_unit_type)
   field MAY be changed, e.g. when it is desirable to handle a CRA
   picture to be a BLA picture [JCTVC-J0107].

   The DONL field, when present, specifies the value of the 16 least
   significant bits of the decoding order number of the contained NAL
   unit.  If tx-mode is equal to "MSM" or sprop-max-don-diff is greater
   than 0, the DONL field MUST be present, and the variable DON for the
   contained NAL unit is derived as equal to the value of the DONL
   field.  Otherwise (tx-mode is equal to "SSM" and sprop-max-don-diff
   is equal to 0), the DONL field MUST NOT be present.







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4.7 Aggregation Packets (APs)

   Aggregation packets (APs) are introduced to enable the reduction of
   packetization overhead for small NAL units, such as most of the non-
   VCL NAL units, which are often only a few octets in size.

   An AP aggregates NAL units within one access unit.  Each NAL unit to
   be carried in an AP is encapsulated in an aggregation unit.  NAL
   units aggregated in one AP are in NAL unit decoding order.

   An AP consists of a payload header (denoted as PayloadHdr) followed
   by two or more aggregation units, as shown in Figure 4.

   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    PayloadHdr (Type=48)       |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   |             two or more aggregation units                     |
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 4 The structure of an aggregation packet

   The fields in the payload header are set as follows.  The F bit MUST
   be equal to 0 if the F bit of each aggregated NAL unit is equal to
   zero; otherwise, it MUST be equal to 1.  The Type field MUST be
   equal to 48.  The value of LayerId MUST be equal to the lowest value
   of LayerId of all the aggregated NAL units.  The value of TID MUST
   be the lowest value of TID of all the aggregated NAL units.

      Informative Note: All VCL NAL units in an AP have the same TID
      value since they belong to the same access unit.  However, an AP
      may contain non-VCL NAL units for which the TID value in the NAL
      unit header may be different than the TID value of the VCL NAL
      units in the same AP.





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   An AP MUST carry at least two aggregation units and can carry as
   many aggregation units as necessary; however, the total amount of
   data in an AP obviously MUST fit into an IP packet, and the size
   SHOULD be chosen so that the resulting IP packet is smaller than the
   MTU size so to avoid IP layer fragmentation.  An AP MUST NOT contain
   Fragmentation Units (FUs) specified in section 4.8.  APs MUST NOT be
   nested; i.e. an AP MUST NOT contain another AP.

   The first aggregation unit in an AP consists of a conditional 16-bit
   DONL field (in network byte order) followed by a 16-bit unsigned
   size information (in network byte order) that indicates the size of
   the NAL unit in bytes (excluding these two octets, but including the
   NAL unit header), followed by the NAL unit itself, including its NAL
   unit header, as shown in Figure 5.

   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   :       DONL (conditional)      |   NALU size   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   NALU size   |                                               |
   +-+-+-+-+-+-+-+-+         NAL unit                              |
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 5 The structure of the first aggregation unit in an AP

   The DONL field, when present, specifies the value of the 16 least
   significant bits of the decoding order number of the aggregated NAL
   unit.

   If tx-mode is equal to "MSM" or sprop-max-don-diff is greater than
   0, the DONL field MUST be present in an aggregation unit that is the
   first aggregation unit in an AP, and the variable DON for the
   aggregated NAL unit is derived as equal to the value of the DONL
   field.  Otherwise (tx-mode is equal to "SSM" and sprop-max-don-diff
   is equal to 0), the DONL field MUST NOT be present in an aggregation
   unit that is the first aggregation unit in an AP.



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   An aggregation unit that is not the first aggregation unit in an AP
   consists of a conditional 8-bit DOND field followed by a 16-bit
   unsigned size information (in network byte order) that indicates the
   size of the NAL unit in bytes (excluding these two octets, but
   including the NAL unit header), followed by the NAL unit itself,
   including its NAL unit header, as shown in Figure 6.

   0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   : DOND (cond)   |          NALU size            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                       NAL unit                                |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 6 The structure of an aggregation unit that is not the first
                         aggregation unit in an AP

   When present, the DOND field plus 1 specifies the difference between
   the decoding order number values of the current aggregated NAL unit
   and the preceding aggregated NAL unit in the same AP.

   If tx-mode is equal to "MSM" or sprop-max-don-diff is greater than
   0, the DOND field MUST be present in an aggregation unit that is not
   the first aggregation unit in an AP, and the variable DON for the
   aggregated NAL unit is derived as equal to the DON of the preceding
   aggregated NAL unit in the same AP plus the value of the DOND field
   plus 1 modulo 65536.  Otherwise (tx-mode is equal to "SSM" and
   sprop-max-don-diff is equal to 0), the DOND field MUST NOT be
   present in an aggregation unit that is not the first aggregation
   unit in an AP, and in this case the transmission order and decoding
   order of NAL units carried in the AP are the same as the order the
   NAL units appear in the AP.

   Figure 7 presents an example of an AP that contains two aggregation
   units, labeled as 1 and 2 in the figure, without the DONL and DOND
   fields being present.



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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          RTP Header                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   PayloadHdr (Type=48)        |         NALU 1 Size           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          NALU 1 HDR           |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         NALU 1 Data           |
   |                   . . .                                       |
   |                                                               |
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  . . .        | NALU 2 Size                   | NALU 2 HDR    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | NALU 2 HDR    |                                               |
   +-+-+-+-+-+-+-+-+              NALU 2 Data                      |
   |                   . . .                                       |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 7 An example of an AP packet containing two aggregation units
                     without the DONL and DOND fields

   Figure 8 presents an example of an AP that contains two aggregation
   units, labeled as 1 and 2 in the figure, with the DONL and DOND
   fields being present.


















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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          RTP Header                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   PayloadHdr (Type=48)        |        NALU 1 DONL            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          NALU 1 Size          |            NALU 1 HDR         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                 NALU 1 Data   . . .                           |
   |                                                               |
   +     . . .     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |  NALU 2 DOND  |          NALU 2 Size          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          NALU 2 HDR           |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          NALU 2 Data          |
   |                                                               |
   |        . . .                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 8 An example of an AP containing two aggregation units with
                         the DONL and DOND fields

4.8 Fragmentation Units (FUs)

   Fragmentation units (FUs) are introduced to enable fragmenting a
   single  NAL  unit  into  multiple  RTP  packets,  possibly  without
   cooperation or knowledge of the HEVC encoder.  A fragment of a NAL
   unit consists of an integer number of consecutive octets of that NAL
   unit.  Fragments of the same NAL unit MUST be sent in consecutive
   order with ascending RTP sequence numbers (with no other RTP packets
   within the same RTP stream being sent between the first and last
   fragment).

   When a NAL unit is fragmented and conveyed within FUs, it is
   referred to as a fragmented NAL unit.  APs MUST NOT be fragmented.
   FUs MUST NOT be nested; i.e. an FU MUST NOT contain a subset of
   another FU.



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   The RTP timestamp of an RTP packet carrying an FU is set to the
   NALU-time of the fragmented NAL unit.

   An FU consists of a payload header (denoted as PayloadHdr), an FU
   header of one octet, a conditional 16-bit DONL field (in network
   byte order), and an FU payload, as shown in Figure 9.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    PayloadHdr (Type=49)       |   FU header   | DONL (cond)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
   | DONL (cond)   |                                               |
   |-+-+-+-+-+-+-+-+                                               |
   |                         FU payload                            |
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 9 The structure of an FU

   The fields in the payload header are set as follows.  The Type field
   MUST be equal to 49.  The fields F, LayerId, and TID MUST be equal
   to the fields F, LayerId, and TID, respectively, of the fragmented
   NAL unit.

   The FU header consists of an S bit, an E bit, and a 6-bit FuType
   field, as shown in Figure 10.

                            +---------------+
                            |0|1|2|3|4|5|6|7|
                            +-+-+-+-+-+-+-+-+
                            |S|E|  FuType   |
                            +---------------+

                  Figure 10   The structure of FU header







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   The semantics of the FU header fields are as follows:
   S: 1 bit
      When set to one, the S bit indicates the start of a fragmented
      NAL unit i.e. the first byte of the FU payload is also the first
      byte of the payload of the fragmented NAL unit.  When the FU
      payload is not the start of the fragmented NAL unit payload, the
      S bit MUST be set to zero.

   E: 1 bit
      When set to one, the E bit indicates the end of a fragmented NAL
      unit, i.e. the last byte of the payload is also the last byte of
      the fragmented NAL unit.  When the FU payload is not the last
      fragment of a fragmented NAL unit, the E bit MUST be set to zero.

   FuType: 6 bits
      The field FuType MUST be equal to the field Type of the
      fragmented NAL unit.

   The DONL field, when present, specifies the value of the 16 least
   significant bits of the decoding order number of the fragmented NAL
   unit.

   If tx-mode is equal to "MSM" or sprop-max-don-diff is greater than
   0, and the S bit is equal to 1, the DONL field MUST be present in
   the FU, and the variable DON for the fragmented NAL unit is derived
   as equal to the value of the DONL field.  Otherwise (tx-mode is
   equal to "SSM" and sprop-max-don-diff is equal to 0, or the S bit is
   equal to 0), the DONL field MUST NOT be present in the FU.

   A non-fragmented NAL unit MUST NOT be transmitted in one FU; i.e.
   the Start bit and End bit MUST NOT both be set to one in the same FU
   header.

   The FU payload consists of fragments of the payload of the
   fragmented NAL unit so that if the FU payloads of consecutive FUs,
   starting with an FU with the S bit equal to 1 and ending with an FU
   with the E bit equal to 1, are sequentially concatenated, the
   payload of the fragmented NAL unit can be reconstructed.  The NAL
   unit header of the fragmented NAL unit is not included as such in



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   the FU payload, but rather the information of the NAL unit header of
   the fragmented NAL unit is conveyed in F, LayerId, and TID fields of
   the FU payload headers of the FUs and the FuType field of the FU
   header of the FUs.  An FU payload MUST not be empty.

   If an FU is lost, the receiver SHOULD discard all following
   fragmentation units in transmission order corresponding to the same
   fragmented NAL unit, unless the decoder in the receiver is known to
   be prepared to gracefully handle incomplete NAL units.

   A receiver in an endpoint or in a MANE MAY aggregate the first n-1
   fragments of a NAL unit to an (incomplete) NAL unit, even if
   fragment n of that NAL unit is not received.  In this case, the
   forbidden_zero_bit of the NAL unit MUST be set to one to indicate a
   syntax violation.

4.9 PACI packets

   This section specifies the PACI packet structure.  The basic payload
   header specified in this memo is intentionally limited to the 16
   bits of the NAL unit header so to keep the packetization overhead to
   a minimum.  However, cases have been identified where it is
   advisable to include control information in an easily accessible
   position in the packet header, despite the additional overhead.  One
   such control information is the Temporal Scalability Control
   Information as specified in section 4.10 below.  PACI packets carry
   this and future, similar structures.

   The PACI packet structure is based on a payload header extension
   mechanism that is generic and extensible to carry payload header
   extensions.  In this section, the focus lies on the use within this
   specification.  Section 4.9.2 below provides guidance for the
   specification designers in how to employ the extension mechanism in
   future specifications.

   A PACI packet consists of a payload header (denoted as PayloadHdr),
   for which the structure follows what is described in section 4.3
   above.  The payload header is followed by the fields A, cType,
   PHSsize, F[0..2] and Y.





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   Figure 11 shows a PACI packet in compliance with this memo; that is,
   without any extensions.

      0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    PayloadHdr (Type=50)       |A|   cType   | PHSsize |F0..2|Y|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Payload Header Extension Structure (PHES)              |
      |=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=|
      |                                                               |
      |                  PACI payload: NAL unit                       |
      |                   . . .                                       |
      |                                                               |
      |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               :...OPTIONAL RTP padding        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

                    Figure 11   The structure of a PACI

   The fields in the payload header are set as follows.  The F bit MUST
   be equal to 0.  The Type field MUST be equal to 50.  The value of
   LayerId MUST be a copy of the LayerId field of the PACI payload NAL
   unit or NAL-unit-like structure.  The value of TID MUST be a copy of
   the TID field of the PACI payload NAL unit or NAL-unit-like
   structure.

   The semantics of other fields are as follows:

   A: 1 bit
      Copy of the F bit of the PACI payload NAL unit or NAL-unit-like
      structure.

   cType: 6 bits
      Copy of the Type field of the PACI payload NAL unit or NAL-unit-
      like structure.







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   PHSsize: 5 bits
      Indicates the total length of the fields F[0..2], Y, and PHES.
      The value is limited to be less than or equal to 32 octets, to
      simplify encoder design for MTU size matching.

   F0
      This field equal to 1 specifies the presence of a temporal
      scalability support extension in the PHES.

   F1, F2
      MUST be 0, available for future extensions, see section 4.9.2.

   Y: 1 bit
      MUST be 0, available for future extensions, see section 4.9.2.

   PHES: variable number of octets
      A variable number of octets as indicated by the value of PHSsize.

   PACI Payload
      The NAL unit or NAL-unit-like structure (such as: FU or AP) to be
      carried, not including the first two octets.

         Informative note: The first two octets of the NAL unit or NAL-
         unit-like structure carried in the PACI payload are not
         included in the PACI payload. Rather, the respective values
         are copied in locations of the PayloadHdr of the RTP packet.
         This design offers two advantages: first, the overall
         structure of the payload header is preserved, i.e. there is no
         special case of payload header structure that needs to be
         implemented for PACI.  Second, no additional overhead is
         introduced.

      A PACI payload MAY be a single NAL unit, an FU, or an AP.  PACIs
      MUST NOT be fragmented or aggregated.  The following subsection
      documents the reasons for these design choices.






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4.9.1 Reasons for the PACI rules (informative)

   A PACI cannot be fragmented.  If a PACI could be fragmented, and a
   fragment other than the first fragment would get lost, access to the
   information in the PACI would not be possible.  Therefore, a PACI
   must not be fragmented.  In other words, an FU must not carry
   (fragments of) a PACI.

   A PACI cannot be aggregated.  Aggregation of PACIs is inadvisable
   from a compression viewpoint, as, in many cases, several to be
   aggregated NAL units would share identical PACI fields and values
   which would be carried redundantly for no reason.   Most, if not all
   the practical effects of PACI aggregation can be achieved by
   aggregating NAL units and bundling them with a PACI (see below).
   Therefore, a PACI must not be aggregated.  In other words, an AP
   must not contain a PACI.

   The payload of a PACI can be a fragment.  Both middleboxes and
   sending systems with inflexible (often hardware-based) encoders
   occasionally find themselves in situations where a PACI and its
   headers, combined, are larger than the MTU size.  In such a
   scenario, the middlebox or sender can fragment the NAL unit and
   encapsulate the fragment in a PACI.  Doing so preserves the payload
   header extension information for all fragments, allowing downstream
   middleboxes and the receiver to take advantage of that information.
   Therefore, a sender may place a fragment into a PACI, and a receiver
   must be able to handle such a PACI.

   The payload of a PACI can be an aggregation NAL unit.  HEVC
   bitstreams can contain unevenly sized and/or small (when compared to
   the MTU size) NAL units.  In order to efficiently packetize such
   small NAL units, AP were introduced.  The benefits of APs are
   independent from the need for a payload header extension.
   Therefore, a sender may place an AP into a PACI, and a receiver must
   be able to handle such a PACI.

4.9.2 PACI extensions (Informative)

   This subsection includes recommendations for future specification
   designers on how to extent the PACI syntax to accommodate future
   extensions.  Obviously, designers are free to specify whatever


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   appears to be appropriate to them at the time of their design.
   However, a lot of thought has been invested into the extension
   mechanism described below, and we suggest that deviations from it
   warrant a good explanation.

   This memo defines only a single payload header extension (Temporal
   Scalability Control Information, described below in section 4.10),
   and, therefore, only the F0 bit carries semantics.  F1 and F2 are
   already named (and not just marked as reserved, as a typical video
   spec designer would do).  They are intended to signal two additional
   extensions.  The Y bit allows to, recursively, add further F and Y
   bits to extend the mechanism beyond 3 possible payload header
   extensions.  It is suggested to define a new packet type (using a
   different value for Type) when assigning the F1, F2, or Y bits
   different semantics than what is suggested below.

   When a Y bit is set, an 8 bit flag-extension is inserted after the Y
   bit.  A flag-extension consists of 7 flags F[n..n+6], and another Y
   bit.

   The basic PACI header already includes F0, F1, and F2.  Therefore,
   the Fx bits in the first flag-extensions are numbered F3, F4, ...,
   F9, the F bits in the second flag-extension are numbered F10, F11,
   ..., F16, and so forth.  As a result, at least 3 Fx bits are always
   in the PACI, but the number of Fx bits (and associated types of
   extensions), can be increased by setting the next Y bit and adding
   an octet of flag-extensions, carrying 7 flags and another Y bit.
   The size of this list of flags is subject to the limits specified in
   section 4.9 (32 octets for all flag-extensions and the PHES
   information combined).

   Each of the F bits can indicate either the presence of information
   in the Payload Header Extension Structure (PHES), described below,
   or a given F bit can indicate a certain condition, without including
   additional information in the PHES.

   When a spec developer devises a new syntax that takes advantage of
   the PACI extension mechanism, he/she must follow the constraints
   listed below; otherwise the extension mechanism may break.





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     1) The fields added for a particular Fx bit MUST be fixed in
        length and not depend on what other Fx bits are set (no parsing
        dependency).
     2) The Fx bits must be assigned in order.
     3) An implementation that supports the n-th Fn bit for any value
        of n must understand the syntax (though not necessarily the
        semantics) of the fields Fk (with k < n), so to be able to
        either use those bits when present, or at least be able to skip
        over them.

4.10 Temporal Scalability Control Information

   This section describes the single payload header extension defined
   in this specification, known as Temporal Scalability Control
   Information (TSCI).  If, in the future, additional payload header
   extensions become necessary, they could be specified in this section
   of an updated version of this document, or in their own documents.

   When F0 is set to 1 in a PACI, this specifies that the PHES field
   includes the TSCI fields TL0REFIDX, IrapPicID, S, and E as follows:

     0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    PayloadHdr (Type=50)       |A|   cType   | PHSsize |F0..2|Y|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   TL0REFIDX   |   IrapPicID   |S|E|RES|                       |
      |-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
      |                           ....                                |
      |               PACI payload: NAL unit                          |
      |                                                               |
      |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               :...OPTIONAL RTP padding        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 12   The structure of a PACI with a PHES containing a TSCI








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   TL0PICIDX (8 bits)
      When present, the TL0PICIDX field MUST be set to equal to
      temporal_sub_layer_zero_idx as specified in Section D.3.32 of
      [H.265] for the access unit containing the NAL unit in the PACI.

   IrapPicID (8 bits)
      When present, the IrapPicID field MUST be set to equal to
      irap_pic_id as specified in Section D.3.22 of [H.265] for the
      access unit containing the NAL unit in the PACI.

   S (1 bit)
      The S bit MUST be set to 1 if any of the following conditions is
      true and MUST be set to 0 otherwise:

      . The NAL unit in the payload of the PACI is the first VCL NAL
        unit, in decoding order, of a picture.
      . The NAL unit in the payload of the PACI is an AP and the NAL
        unit in the first contained aggregation unit is the first VCL
        NAL unit, in decoding order, of a picture.
      . The NAL unit in the payload of the PACI is an FU with its S bit
        equal to 1 and the FU payload containing a fragment of the
        first VCL NAL unit, in decoding order of a picture.

   E (1 bit)
      The E bit MUST be set to 1 if any of the following conditions is
      true and MUST be set to 0 otherwise:

      . The NAL unit in the payload of the PACI is the last VCL NAL
        unit, in decoding order, of a picture.
      . The NAL unit in the payload of the PACI is an AP and the NAL
        unit in the last contained aggregation unit is the last VCL NAL
        unit, in decoding order, of a picture.
      . The NAL unit in the payload of the PACI is an FU with its E bit
        equal to 1 and the FU payload containing a fragment of the last
        VCL NAL unit, in decoding order of a picture.

   RES (2 bits)
      MUST be equal to 0.  Reserved for future extensions.


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   The value of PHSsize MUST be set to 3.  Receivers MUST allow other
   values of the fields F0, F1, F2, Y, and PHSsize, and MUST ignore any
   additional fields, when present, than specified above in the PHES.

5. Packetization Rules

   The following packetization rules apply:

   o  If tx-mode is equal to "MSM" or sprop-max-don-diff is greater
      than 0 for an RTP stream, the transmission order of NAL units
      carried in the RTP stream MAY be different than the NAL unit
      decoding order.  Otherwise (tx-mode is equal to "SSM" and sprop-
      max-don-diff is equal to 0 for an RTP stream), the transmission
      order of NAL units carried in the RTP stream MUST be the same as
      the NAL unit decoding order.

   o  A NAL unit of a small size SHOULD be encapsulated in an
      aggregation packet together with one or more other NAL units in
      order to avoid the unnecessary packetization overhead for small
      NAL units.  For example, non-VCL NAL units such as access unit
      delimiters, parameter sets, or SEI NAL units are typically small
      and can often be aggregated with VCL NAL units without violating
      MTU size constraints.

   o  Each non-VCL NAL unit SHOULD, when possible from an MTU size
      match viewpoint, be encapsulated in an aggregation packet
      together with its associated VCL NAL unit, as typically a non-VCL
      NAL unit would be meaningless without the associated VCL NAL unit
      being available.

   o  For carrying exactly one NAL unit in an RTP packet, a single NAL
      unit packet MUST be used.

6. De-packetization Process

   The general concept behind de-packetization is to get the NAL units
   out of the RTP packets in an RTP stream and all RTP streams the RTP
   stream depends on, if any, and pass them to the decoder in the NAL
   unit decoding order.





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   The de-packetization process is implementation dependent.
   Therefore, the following description should be seen as an example of
   a suitable implementation.  Other schemes may be used as well as
   long as the output for the same input is the same as the process
   described below.  The output is the same when the set of output NAL
   units and their order are both identical.  Optimizations relative to
   the described algorithms are possible.

   All normal RTP mechanisms related to buffer management apply.  In
   particular, duplicated or outdated RTP packets (as indicated by the
   RTP sequences number and the RTP timestamp) are removed.  To
   determine the exact time for decoding, factors such as a possible
   intentional delay to allow for proper inter-stream synchronization
   must be factored in.

   NAL units with NAL unit type values in the range of 0 to 47,
   inclusive may be passed to the decoder.  NAL-unit-like structures
   with NAL unit type values in the range of 48 to 63, inclusive, MUST
   NOT be passed to the decoder.

   The receiver includes a receiver buffer, which is used to compensate
   for transmission delay jitter within individual RTP streams and
   across RTP streams, to reorder NAL units from transmission order to
   the NAL unit decoding order, and to recover the NAL unit decoding
   order in MSM, when applicable.  In this section, the receiver
   operation is described under the assumption that there is no
   transmission delay jitter within an RTP stream and across RTP
   streams.  To make a difference from a practical receiver buffer that
   is also used for compensation of transmission delay jitter, the
   receiver buffer is here after called the de-packetization buffer in
   this section.  Receivers should also prepare for transmission delay
   jitter; i.e. either reserve separate buffers for transmission delay
   jitter buffering and de-packetization buffering or use a receiver
   buffer for both transmission delay jitter and de-packetization.
   Moreover, receivers should take transmission delay jitter into
   account in the buffering operation; e.g. by additional initial
   buffering before starting of decoding and playback.

   If only one RTP stream is being received and sprop-max-don-diff of
   the only RTP stream being received is equal to 0, the de-
   packetization buffer size is zero bytes, i.e. the NAL units carried


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   in the RTP stream are directly passed to the decoder in their
   transmission order, which is identical to the decoding order of the
   NAL units. Otherwise, the process described in the remainder of this
   section applies.

   There are two buffering states in the receiver: initial buffering
   and buffering while playing.  Initial buffering starts when the
   reception is initialized.  After initial buffering, decoding and
   playback are started, and the buffering-while-playing mode is used.

   Regardless of the buffering state, the receiver stores incoming NAL
   units, in reception order, into the de-packetization buffer.  NAL
   units carried in RTP packets are stored in the de-packetization
   buffer individually, and the value of AbsDon is calculated and
   stored for each NAL unit.  When MSM is in use, NAL units of all RTP
   streams of a bitstream are stored in the same de-packetization
   buffer.  When NAL units carried in any two RTP streams are available
   to be placed into the de-packetization buffer, those NAL units
   carried in the RTP stream that is lower in the dependency tree are
   placed into the buffer first.  For example, if RTP stream A depends
   on RTP stream B, then NAL units carried in RTP stream B are placed
   into the buffer first.

   Initial buffering lasts until condition A (the difference between
   the greatest and smallest AbsDon values of the NAL units in the de-
   packetization buffer is greater than or equal to the value of sprop-
   max-don-diff of the highest RTP stream) or condition B (the number
   of NAL units in the de-packetization buffer is greater than the
   value of sprop-depack-buf-nalus) is true.

   After initial buffering, whenever condition A or condition B is
   true, the following operation is repeatedly applied until both
   condition A and condition A become false:

   o  The NAL unit in the de-packetization buffer with the smallest
      value of AbsDon is removed from the de-packetization buffer and
      passed to the decoder.

   When no more NAL units are flowing into the de-packetization buffer,
   all NAL units remaining in the de-packetization buffer are removed




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   from the buffer and passed to the decoder in the order of increasing
   AbsDon values.

7. Payload Format Parameters

   This section specifies the parameters that MAY be used to select
   optional features of the payload format and certain features or
   properties of the bitstream or the RTP stream.  The parameters are
   specified here as part of the media type registration for the HEVC
   codec.  A mapping of the parameters into the Session Description
   Protocol (SDP) [RFC4566] is also provided for applications that use
   SDP.  Equivalent parameters could be defined elsewhere for use with
   control protocols that do not use SDP.

7.1 Media Type Registration

   The media subtype for the HEVC codec is allocated from the IETF
   tree.

   The receiver MUST ignore any unrecognized parameter.

   Media Type name:     video

   Media subtype name:  H265

   Required parameters: none

   OPTIONAL parameters:

      profile-space, tier-flag, profile-id, profile-compatibility-
      indicator, interop-constraints, and level-id:

         These parameters indicate the profile, tier, default level,
         and some constraints of the bitstream carried by the RTP
         stream and all RTP streams the RTP stream depends on, or a
         specific set of the profile, tier, default level, and some
         constraints the receiver supports.

         The profile and some constraints are indicated collectively by
         profile-space, profile-id, profile-compatibility-indicator,
         and interop-constraints.  The profile specifies the subset of



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         coding tools that may have been used to generate the bitstream
         or that the receiver supports.

            Informative note: There are 32 values of profile-id, and
            there are 32 flags in profile-compatibility-indicator, each
            flag corresponding to one value of profile-id.  According
            to HEVC version 1 in [HEVC], when more than one of the 32
            flags is set for a bitstream, the bitstream would comply
            with all the profiles corresponding to the set flags.
            However, in a draft of HEVC version 2 in [HEVC draft v2],
            subclause A.3.5, 19 Format Range Extensions profiles have
            been specified, all using the same value of profile-id (4),
            differentiated by some of the 48 bits in interop-
            constraints - this (rather unexpected way of profile
            signalling) means that one of the 32 flags may correspond
            to multiple profiles.  To be able to support whatever HEVC
            extension profile that might be specified and indicated
            using profile-space, profile-id, profile-compatibility-
            indicator, and interop-constraints in the future, it would
            be safe to require symmetric use of these parameters in SDP
            offer/answer unless recv-sub-layer-id is included in the
            SDP answer for choosing one of the sub-layers offered.

         The tier is indicated by tier-flag.  The default level is
         indicated by level-id.  The tier and the default level specify
         the limits on values of syntax elements or arithmetic
         combinations of values of syntax elements that are followed
         when generating the bitstream or that the receiver supports.

         A set of profile-space, tier-flag, profile-id, profile-
         compatibility-indicator, interop-constraints, and level-id
         parameters ptlA is said to be consistent with another set of
         these parameters ptlB if any decoder that conforms to the
         profile, tier, level, and constraints indicated by ptlB can
         decode any bitstream that conforms to the profile, tier,
         level, and constraints indicated by ptlA.

         In SDP offer/answer, when the SDP answer does not include the
         recv-sub-layer-id parameter that is less than the sprop-sub-
         layer-id parameter in the SDP offer, the following applies:



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            o The profile-space, tier-flag, profile-id, profile-
              compatibility-indicator, and interop-constraints
              parameters MUST be used symmetrically, i.e. the value of
              each of these parameters in the offer MUST be the same as
              that in the answer, either explicitly signalled or
              implicitly inferred.
            o The level-id parameter is changeable as long as the
              highest level indicated by the answer is either equal to
              or lower than that in the offer.  Note that the highest
              level is indicated by level-id and max-recv-level-id
              together.

         In SDP offer/answer, when the SDP answer does include the
         recv-sub-layer-id parameter that is less than the sprop-sub-
         layer-id parameter in the SDP offer, the set of profile-space,
         tier-flag, profile-id, profile-compatibility-indicator,
         interop-constraints, and level-id parameters included in the
         answer MUST be consistent with that for the chosen sub-layer
         representation as indicated in the SDP offer, with the
         exception that the level-id parameter in the SDP answer is
         changable as long as the highest level indicated by the answer
         is either lower than or equal to that in the offer.

         More specifications of these parameters, including how they
         relate to the values of the profile, tier, and level syntax
         elements specified in [HEVC] are provided below.

      profile-space, profile-id:

         The value of profile-space MUST be in the range of 0 to 3,
         inclusive.  The value of profile-id MUST be in the range of 0
         to 31, inclusive.

         When profile-space is not present, a value of 0 MUST be
         inferred.  When profile-id is not present, a value of 1 (i.e.
         the Main profile) MUST be inferred.

         When used to indicate properties of a bitstream, profile-space
         and profile-id are derived from the profile, tier, and level
         syntax elements in SPS or VPS NAL units as follows, where
         general_profile_space, general_profile_idc,


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         sub_layer_profile_space[j], and sub_layer_profile_idc[j] are
         specified in [HEVC]:

            If the RTP stream is the highest RTP stream, the following
            applies:

            o profile_space = general_profile_space
            o profile_id = general_profile_idc

            Otherwise (the RTP stream is a dependee RTP stream), the
            following applies, with j being the value of the sprop-sub-
            layer-id parameter:

            o profile_space = sub_layer_profile_space[j]
            o profile_id = sub_layer_profile_idc[j]

      tier-flag, level-id:

         The value of tier-flag MUST be in the range of 0 to 1,
         inclusive.  The value of level-id MUST be in the range of 0
         to 255, inclusive.

         If the tier-flag and level-id parameters are used to indicate
         properties of a bitstream, they indicate the tier and the
         highest level the bitstream complies with.

         If the tier-flag and level-id parameters are used for
         capability exchange, the following applies.  If max-recv-
         level-id is not present, the default level defined by level-id
         indicates the highest level the codec wishes to support.
         Otherwise, max-recv-level-id indicates the highest level the
         codec supports for receiving.  For either receiving or
         sending, all levels that are lower than the highest level
         supported MUST also be supported.

         If no tier-flag is present, a value of 0 MUST be inferred and
         if no level-id is present, a value of 93 (i.e. level 3.1) MUST
         be inferred.

         When used to indicate properties of a bitstream, the tier-flag
         and level-id parameters are derived from the profile, tier,



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         and level syntax elements in SPS or VPS NAL units as follows,
         where general_tier_flag, general_level_idc,
         sub_layer_tier_flag[j], and sub_layer_level_idc[j] are
         specified in [HEVC]:

            If the RTP stream is the highest RTP stream, the following
            applies:

            o tier-flag = general_tier_flag
            o level-id = general_level_idc

            Otherwise (the RTP stream is a dependee RTP stream), the
            following applies, with j being the value of the sprop-sub-
            layer-id parameter:

            o tier-flag = sub_layer_tier_flag[j]
            o level-id = sub_layer_level_idc[j]

      interop-constraints:

         A base16 [RFC4648] (hexadecimal) representation of six bytes
         of data, consisting of progressive_source_flag,
         interlaced_source_flag, non_packed_constraint_flag,
         frame_only_constraint_flag, and reserved_zero_44bits.

         If the interop-constraints parameter is not present, the
         following MUST be inferred:

            o progressive_source_flag = 1
            o interlaced_source_flag = 0
            o non_packed_constraint_flag = 1
            o frame_only_constraint_flag = 1
            o reserved_zero_44bits = 0

         When the interop-constraints parameter is used to indicate
         properties of a bitstream, the following applies, where
         general_progressive_source_flag,
         general_interlaced_source_flag,
         general_non_packed_constraint_flag,
         general_non_packed_constraint_flag,
         general_frame_only_constraint_flag,



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         general_reserved_zero_44bits,
         sub_layer_progressive_source_flag[j],
         sub_layer_interlaced_source_flag[j],
         sub_layer_non_packed_constraint_flag[j],
         sub_layer_frame_only_constraint_flag[j], and
         sub_layer_reserved_zero_44bits[j] are specified in [HEVC]:

            If the RTP stream is the highest RTP stream, the following
            applies:

            o progressive_source_flag = general_progressive_source_flag
            o interlaced_source_flag = general_interlaced_source_flag
            o non_packed_constraint_flag =
                              general_non_packed_constraint_flag
            o frame_only_constraint_flag =
                              general_frame_only_constraint_flag
            o reserved_zero_44bits = general_reserved_zero_44bits

            Otherwise (the RTP stream is a dependee RTP stream), the
            following applies, with j being the value of the sprop-sub-
            layer-id parameter:

            o progressive_source_flag =
                              sub_layer_progressive_source_flag[j]
            o interlaced_source_flag =
                              sub_layer_interlaced_source_flag[j]
            o non_packed_constraint_flag =
                              sub_layer_non_packed_constraint_flag[j]
            o frame_only_constraint_flag =
                              sub_layer_frame_only_constraint_flag[j]
            o reserved_zero_44bits = sub_layer_reserved_zero_44bits[j]

         Using interop-constraints for capability exchange results in a
         requirement on any bitstream to be compliant with the interop-
         constraints.

      profile-compatibility-indicator:

         A base16 [RFC4648] representation of four bytes of data.





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         When profile-compatibility-indicator is used to indicate
         properties of a bitstream, the following applies, where
         general_profile_compatibility_flag[j] and
         sub_layer_profile_compatibility_flag[i][j] are specified in
         [HEVC]:

            The profile-compatibility-indicator in this case indicates
            additional profiles to the profile defined by
            profile_space, profile_id, and interop-constraints the
            bitstream conforms to.  A decoder that conforms to any of
            all the profiles the bitstream conforms to would be capable
            of decoding the bitstream.  These additional profiles are
            defined by profile-space, each set bit of profile-
            compatibility-indicator, and interop-constraints.

            If the RTP stream is the highest RTP stream, the following
            applies for each value of j in the range of 0 to 31,
            inclusive:

            o bit j of profile-compatibility-indicator =
                  general_profile_compatibility_flag[j]

            Otherwise (the RTP stream is a dependee RTP stream), the
            following applies for i equal to sprop-sub-layer-id and for
            each value of j in the range of 0 to 31, inclusive:

            o bit j of profile-compatibility-indicator =
                  sub_layer_profile_compatibility_flag[i][j]

         Using profile-compatibility-indicator for capability exchange
         results in a requirement on any bitstream to be compliant with
         the profile-compatibility-indicator.  This is intended to
         handle cases where any future HEVC profile is defined as an
         intersection of two or more profiles.

         If this parameter is not present, this parameter defaults to
         the following: bit j, with j equal to profile-id, of profile-
         compatibility-indicator is inferred to be equal to 1, and all
         other bits are inferred to be equal to 0.





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      sprop-sub-layer-id:

         This parameter MAY be used to indicate the highest allowed
         value of TID in the bitstream.  When not present, the value of
         sprop-sub-layer-id is inferred to be equal to 6.

         The value of sprop-sub-layer-id MUST be in the range of 0
         to 6, inclusive.

      recv-sub-layer-id:

         This parameter MAY be used to signal a receiver's choice of
         the offered or declared sub-layer representations in the
         sprop-vps.  The value of recv-sub-layer-id indicates the TID
         of the highest sub-layer of the bitstream that a receiver
         supports.  When not present, the value of recv-sub-layer-id is
         inferred to be equal to the value of the sprop-sub-layer-id
         parameter in the SDP offer.

         The value of recv-sub-layer-id MUST be in the range of 0 to 6,
         inclusive.

      max-recv-level-id:

         This parameter MAY be used to indicate the highest level a
         receiver supports.  The highest level the receiver supports is
         equal to the value of max-recv-level-id divided by 30.

         The value of max-recv-level-id MUST be in the range of 0
         to 255, inclusive.

         When max-recv-level-id is not present, the value is inferred
         to be equal to level-id.

         max-recv-level-id MUST NOT be present when the highest level
         the receiver supports is not higher than the default level.

      tx-mode:

         This parameter indicates whether the transmission mode is SSM
         or MSM.



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         The value of tx-mode MUST be equal to either "MSM" or "SSM".
         When not present, the value of tx-mode is inferred to be equal
         to "SSM".

         If the value is equal to "MSM", MSM MUST be in use.  Otherwise
         (the value is equal to "SSM"), SSM MUST be in use.

         The value of tx-mode MUST be equal to "MSM" for all RTP
         sessions in an MSM.

      sprop-vps:

         This parameter MAY be used to convey any video parameter set
         NAL unit of the bitstream for out-of-band transmission of
         video parameter sets.  The parameter MAY also be used for
         capability exchange and to indicate sub-stream characteristics
         (i.e. properties of sub-layer representations as defined in
         [HEVC]).  The value of the parameter is a comma-separated
         (',') list of base64 [RFC4648] representations of the video
         parameter set NAL units as specified in Section 7.3.2.1 of
         [HEVC].

         The sprop-vps parameter MAY contain one or more than one video
         parameter set NAL unit. However, all other video parameter
         sets contained in the sprop-vps parameter MUST be consistent
         with the first video parameter set in the sprop-vps parameter.
         A video parameter set vpsB is said to be consistent with
         another video parameter set vpsA if any decoder that conforms
         to the profile, tier, level, and constraints indicated by the
         12 bytes of data starting from the syntax element
         general_profile_space to the syntax element general_level_id,
         inclusive, in the first profile_tier_level( ) syntax structure
         in vpsA can decode any bitstream that conforms to the profile,
         tier, level, and constraints indicated by the 12 bytes of data
         starting from the syntax element general_profile_space to the
         syntax element general_level_id, inclusive, in the first
         profile_tier_level( ) syntax structure in vpsB.







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      sprop-sps:

         This parameter MAY be used to convey sequence parameter set
         NAL units of the bitstream for out-of-band transmission of
         sequence parameter sets.  The value of the parameter is a
         comma-separated (',') list of base64 [RFC4648] representations
         of the sequence parameter set NAL units as specified in
         Section 7.3.2.2 of [HEVC].

      sprop-pps:

         This parameter MAY be used to convey picture parameter set NAL
         units of the bitstream for out-of-band transmission of picture
         parameter sets.  The value of the parameter is a comma-
         separated (',') list of base64 [RFC4648] representations of
         the picture parameter set NAL units as specified in Section
         7.3.2.3 of [HEVC].

      sprop-sei:

         This parameter MAY be used to convey one or more SEI messages
         that describe bitstream characteristics.  When present, a
         decoder can rely on the bitstream characteristics that are
         described in the SEI messages for the entire duration of the
         session, independently from the persistence scopes of the SEI
         messages as specified in [HEVC].

         The value of the parameter is a comma-separated (',') list of
         base64 [RFC4648] representations of SEI NAL units as specified
         in Section 7.3.2.4 of [HEVC].

            Informative note: Intentionally, no list of applicable or
            inapplicable SEI messages is specified here.  Conveying
            certain SEI messages in sprop-sei may be sensible in some
            application scenarios and meaningless in others.  However,
            a few examples are described below:

           1) In an environment where the bitstream was created from
               film-based source material, and no splicing is going to
               occur during the lifetime of the session, the film grain
               characteristics SEI message or the tone mapping



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               information SEI message are likely meaningful, and
               sending them in sprop-sei rather than in the bitstream
               at each entry point may help saving bits and allows to
               configure the renderer only once, avoiding unwanted
               artifacts.
           2) The structure of pictures information SEI message in
               sprop-sei can be used to inform a decoder of information
               on the NAL unit types, picture order count values, and
               prediction dependencies of a sequence of pictures.
               Having such knowledge can be helpful for error recovery.
           3) Examples for SEI messages that would be meaningless to
               be conveyed in sprop-sei include the decoded picture
               hash SEI message (it is close to impossible that all
               decoded pictures have the same hash-tag), the display
               orientation SEI message when the device is a handheld
               device (as the display orientation may change when the
               handheld device is turned around), or the filler payload
               SEI message (as there is no point in just having more
               bits in SDP).

      max-lsr, max-lps, max-cpb, max-dpb, max-br, max-tr, max-tc:

         These parameters MAY be used to signal the capabilities of a
         receiver implementation.  These parameters MUST NOT be used
         for any other purpose.  The highest level (specified by max-
         recv-level-id) MUST be such that the receiver is fully capable
         of supporting.  max-lsr, max-lps, max-cpb, max-dpb, max-br,
         max-tr, and max-tc MAY be used to indicate capabilities of the
         receiver that extend the required capabilities of the highest
         level, as specified below.

         When more than one parameter from the set (max-lsr, max-lps,
         max-cpb, max-dpb, max-br, max-tr, max-tc) is present, the
         receiver MUST support all signaled capabilities
         simultaneously.  For example, if both max-lsr and max-br are
         present, the highest level with the extension of both the
         picture rate and bitrate is supported.  That is, the receiver
         is able to decode bitstreams in which the luma sample rate is
         up to max-lsr (inclusive), the bitrate is up to max-br
         (inclusive), the coded picture buffer size is derived as
         specified in the semantics of the max-br parameter below, and


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         the other properties comply with the highest level specified
         by max-recv-level-id.

            Informative note: When the OPTIONAL media type parameters
            are used to signal the properties of a bitstream, and max-
            lsr, max-lps, max-cpb, max-dpb, max-br, max-tr, and max-tc
            are not present, the values of profile-space, tier-flag,
            profile-id, profile-compatibility-indicator, interop-
            constraints, and level-id must always be such that the
            bitstream complies fully with the specified profile, tier,
            and level.

      max-lsr:
         The value of max-lsr is an integer indicating the maximum
         processing rate in units of luma samples per second.  The max-
         lsr parameter signals that the receiver is capable of decoding
         video at a higher rate than is required by the highest level.

         When max-lsr is signaled, the receiver MUST be able to decode
         bitstreams that conform to the highest level, with the
         exception that the MaxLumaSR value in Table A-2 of [HEVC] for
         the highest level is replaced with the value of max-lsr.
         Senders MAY use this knowledge to send pictures of a given
         size at a higher picture rate than is indicated in the highest
         level.

         When not present, the value of max-lsr is inferred to be equal
         to the value of MaxLumaSR given in Table A-2 of [HEVC] for the
         highest level.

         The value of max-lsr MUST be in the range of MaxLumaSR to
         16 * MaxLumaSR, inclusive, where MaxLumaSR is given in Table
         A-2 of [HEVC] for the highest level.

      max-lps:
         The value of max-lps is an integer indicating the maximum
         picture size in units of luma samples.  The max-lps parameter
         signals that the receiver is capable of decoding larger
         picture sizes than are required by the highest level.  When
         max-lps is signaled, the receiver MUST be able to decode
         bitstreams that conform to the highest level, with the


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         exception that the MaxLumaPS value in Table A-1 of [HEVC] for
         the highest level is replaced with the value of max-lps.
         Senders MAY use this knowledge to send larger pictures at a
         proportionally lower picture rate than is indicated in the
         highest level.

         When not present, the value of max-lps is inferred to be equal
         to the value of MaxLumaPS given in Table A-1 of [HEVC] for the
         highest level.

         The value of max-lps MUST be in the range of MaxLumaPS to
         16 * MaxLumaPS, inclusive, where MaxLumaPS is given in Table
         A-1 of [HEVC] for the highest level.

      max-cpb:
         The value of max-cpb is an integer indicating the maximum
         coded picture buffer size in units of CpbBrVclFactor bits for
         the VCL HRD parameters and in units of CpbBrNalFactor bits for
         the NAL HRD parameters, where CpbBrVclFactor and
         CpbBrNalFactor are defined in Section A.4 of [HEVC].  The max-
         cpb parameter signals that the receiver has more memory than
         the minimum amount of coded picture buffer memory required by
         the highest level.  When max-cpb is signaled, the receiver
         MUST be able to decode bitstreams that conform to the highest
         level, with the exception that the MaxCPB value in Table A-1
         of [HEVC] for the highest level is replaced with the value of
         max-cpb.  Senders MAY use this knowledge to construct coded
         bitstreams with greater variation of bitrate than can be
         achieved with the MaxCPB value in Table A-1 of [HEVC].

         When not present, the value of max-cpb is inferred to be equal
         to the value of MaxCPB given in Table A-1 of [HEVC] for the
         highest level.

         The value of max-cpb MUST be in the range of MaxCPB to
         16 * MaxCPB, inclusive, where MaxLumaCPB is given in Table A-1
         of [HEVC] for the highest level.

            Informative note: The coded picture buffer is used in the
            hypothetical reference decoder (Annex C of HEVC).  The use
            of the hypothetical reference decoder is recommended in


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            HEVC encoders to verify that the produced bitstream
            conforms to the standard and to control the output bitrate.
            Thus, the coded picture buffer is conceptually independent
            of any other potential buffers in the receiver, including
            de-packetization and de-jitter buffers.  The coded picture
            buffer need not be implemented in decoders as specified in
            Annex C of HEVC, but rather standard-compliant decoders can
            have any buffering arrangements provided that they can
            decode standard-compliant bitstreams.  Thus, in practice,
            the input buffer for a video decoder can be integrated with
            de-packetization and de-jitter buffers of the receiver.

      max-dpb:
         The value of max-dpb is an integer indicating the maximum
         decoded picture buffer size in units decoded pictures at the
         MaxLumaPS for the highest level, i.e. the number of decoded
         pictures at the maximum picture size defined by the highest
         level.  The value of max-dpb MUST be in the range of 1 to 16,
         respectively.  The max-dpb parameter signals that the receiver
         has more memory than the minimum amount of decoded picture
         buffer memory required by default, which is MaxDpbPicBuf as
         defined in [HEVC] (equal to 6).  When max-dpb is signaled, the
         receiver MUST be able to decode bitstreams that conform to the
         highest level, with the exception that the MaxDpbPicBuff value
         defined in [HEVC] as 6 is replaced with the value of max-dpb.
         Consequently, a receiver that signals max-dpb MUST be capable
         of storing the following number of decoded pictures
         (MaxDpbSize) in its decoded picture buffer:

                          if( PicSizeInSamplesY <= ( MaxLumaPS >> 2 ) )
              MaxDpbSize = Min( 4 * max-dpb, 16 )
           else if ( PicSizeInSamplesY <= ( MaxLumaPS >> 1 ) )
              MaxDpbSize = Min( 2 * max-dpb, 16 )
           else if ( PicSizeInSamplesY <= ( ( 3 * MaxLumaPS ) >> 2 ) )
              MaxDpbSize = Min( (4 * max-dpb) / 3, 16 )
           else
              MaxDpbSize = max-dpb

                        Wherein MaxLumaPS given in Table A-1 of [HEVC] for the highest
         level and PicSizeInSamplesY is the current size of each
         decoded picture in units of luma samples as defined in [HEVC].


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                        The value of max-dpb MUST be greater than or equal to the
         value of MaxDpbPicBuf (i.e. 6) as defined in [HEVC].  Senders
         MAY use this knowledge to construct coded bitstreams with
         improved compression.

                        When not present, the value of max-dpb is inferred to be equal
         to the value of MaxDpbPicBuf (i.e. 6) as defined in [HEVC].

            Informative note: This parameter was added primarily to
            complement a similar codepoint in the ITU-T Recommendation
            H.245, so as to facilitate signaling gateway designs.  The
            decoded picture buffer stores reconstructed samples.  There
            is no relationship between the size of the decoded picture
            buffer and the buffers used in RTP, especially de-
            packetization and de-jitter buffers.

      max-br:
         The value of max-br is an integer indicating the maximum video
         bitrate in units of CpbBrVclFactor bits per second for the VCL
         HRD parameters and in units of CpbBrNalFactor bits per second
         for the NAL HRD parameters, where CpbBrVclFactor and
         CpbBrNalFactor are defined in Section A.4 of [HEVC].

         The max-br parameter signals that the video decoder of the
         receiver is capable of decoding video at a higher bitrate than
         is required by the highest level.

         When max-br is signaled, the video codec of the receiver MUST
         be able to decode bitstreams that conform to the highest
         level, with the following exceptions in the limits specified
         by the highest level:

          o The value of max-br replaces the MaxBR value in Table A-2
            of [HEVC] for the highest level.
          o When the max-cpb parameter is not present, the result of
            the following formula replaces the value of MaxCPB in Table
            A-1 of [HEVC]:

               (MaxCPB of the highest level) * max-br / (MaxBR of the
               highest level)




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         For example, if a receiver signals capability for Main profile
         Level 2 with max-br equal to 2000, this indicates a maximum
         video bitrate of 2000 kbits/sec for VCL HRD parameters, a
         maximum video bitrate of 2200 kbits/sec for NAL HRD
         parameters, and a CPB size of 2000000 bits (2000000 / 1500000
         * 1500000).

         Senders MAY use this knowledge to send higher bitrate video as
         allowed in the level definition of Annex A of HEVC to achieve
         improved video quality.

         When not present, the value of max-br is inferred to be equal
         to the value of MaxBR given in Table A-2 of [HEVC] for the
         highest level.

         The value of max-br MUST be in the range of MaxBR to
         16 * MaxBR, inclusive, where MaxBR is given in Table A-2 of
         [HEVC] for the highest level.

            Informative note: This parameter was added primarily to
            complement a similar codepoint in the ITU-T Recommendation
            H.245, so as to facilitate signaling gateway designs.  The
            assumption that the network is capable of handling such
            bitrates at any given time cannot be made from the value of
            this parameter.  In particular, no conclusion can be drawn
            that the signaled bitrate is possible under congestion
            control constraints.

      max-tr:
         The value of max-tr is an integer indication the maximum
         number of tile rows.  The max-tr parameter signals that the
         receiver is capable of decoding video with a larger number of
         tile rows than the value allowed by the highest level.

         When max-tr is signaled, the receiver MUST be able to decode
         bitstreams that conform to the highest level, with the
         exception that the MaxTileRows value in Table A-1 of [HEVC]
         for the highest level is replaced with the value of max-tr.






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         Senders MAY use this knowledge to send pictures utilizing a
         larger number of tile rows than the value allowed by the
         highest level.

         When not present, the value of max-tr is inferred to be equal
         to the value of MaxTileRows given in Table A-1 of [HEVC] for
         the highest level.

         The value of max-tr MUST be in the range of MaxTileRows to
         16 * MaxTileRows, inclusive, where MaxTileRows is given in
         Table A-1 of [HEVC] for the highest level.

      max-tc:
         The value of max-tc is an integer indication the maximum
         number of tile columns.  The max-tc parameter signals that the
         receiver is capable of decoding video with a larger number of
         tile columns than the value allowed by the highest level.

         When max-tc is signaled, the receiver MUST be able to decode
         bitstreams that conform to the highest level, with the
         exception that the MaxTileCols value in Table A-1 of [HEVC]
         for the highest level is replaced with the value of max-tc.

         Senders MAY use this knowledge to send pictures utilizing a
         larger number of tile columns than the value allowed by the
         highest level.

         When not present, the value of max-tc is inferred to be equal
         to the value of MaxTileCols given in Table A-1 of [HEVC] for
         the highest level.

         The value of max-tc MUST be in the range of MaxTileCols to
         16 * MaxTileCols, inclusive, where MaxTileCols is given in
         Table A-1 of [HEVC] for the highest level.

      max-fps:

         The value of max-fps is an integer indicating the maximum
         picture rate in units of pictures per 100 seconds that can be
         effectively processed by the receiver.  The max-fps parameter
         MAY be used to signal that the receiver has a constraint in



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         that it is not capable of processing video effectively at the
         full picture rate that is implied by the highest level and,
         when present, one or more of the parameters max-lsr, max-lps,
         and max-br.

         The value of max-fps is not necessarily the picture rate at
         which the maximum picture size can be sent, it constitutes a
         constraint on maximum picture rate for all resolutions.

            Informative note: The max-fps parameter is semantically
            different from max-lsr, max-lps, max-cpb, max-dpb, max-br,
            max-tr, and max-tc in that max-fps is used to signal a
            constraint, lowering the maximum picture rate from what is
            implied by other parameters.

         The encoder MUST use a picture rate equal to or less than this
         value.  In cases where the max-fps parameter is absent the
         encoder is free to choose any picture rate according to the
         highest level and any signaled optional parameters.

         The value of max-fps MUST be smaller than or equal to the full
         picture rate that is implied by the highest level and, when
         present, one or more of the parameters max-lsr, max-lps, and
         max-br.

      sprop-max-don-diff:

         The value of this parameter MUST be equal to 0, if the RTP
         stream does not depend on other RTP streams and there is no
         NAL unit naluA that is followed in transmission order by any
         NAL unit preceding naluA in decoding order.  Otherwise, this
         parameter specifies the maximum absolute difference between
         the decoding order number (i.e., AbsDon) values of any two NAL
         units naluA and naluB, where naluA follows naluB in decoding
         order and precedes naluB in transmission order.

         The value of sprop-max-don-diff MUST be an integer in the
         range of 0 to 32767, inclusive.

         When not present, the value of sprop-max-don-diff is inferred
         to be equal to 0.



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         When the RTP stream depends on one or more other RTP streams
         (in this case tx-mode MUST be equal to "MSM" and MSM is in
         use), this parameter MUST be present and the value MUST be
         greater than 0.

            Informative note: When the RTP stream does not depend on
            other RTP streams, either MSM or SSM may be in use.

      sprop-depack-buf-nalus:

         This parameter specifies the maximum number of NAL units that
         precede a NAL unit in transmission order and follow the NAL
         unit in decoding order.

         The value of sprop-depack-buf-nalus MUST be an integer in the
         range of 0 to 32767, inclusive.

         When not present, the value of sprop-depack-buf-nalus is
         inferred to be equal to 0.

         When the RTP stream depends on one or more other RTP streams
         (in this case tx-mode MUST be equal to "MSM" and MSM is in
         use), this parameter MUST be present and the value MUST be
         greater than 0.

      sprop-depack-buf-bytes:

         This parameter signals the required size of the de-
         packetization buffer in units of bytes.  The value of the
         parameter MUST be greater than or equal to the maximum buffer
         occupancy (in units of bytes) of the de-packetization buffer
         as specified in section 6.

         The value of sprop-depack-buf-bytes MUST be an integer in the
         range of 0 to 4294967295, inclusive.

         When the RTP stream depends on one or more other RTP streams
         (in this case tx-mode MUST be equal to "MSM" and MSM is in
         use) or sprop-max-don-diff is present and greater than 0, this
         parameter MUST be present and the value MUST be greater than
         0.



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            Informative note: The value of sprop-depack-buf-bytes
            indicates the required size of the de-packetization buffer
            only.  When network jitter can occur, an appropriately
            sized jitter buffer has to be available as well.

      depack-buf-cap:

         This parameter signals the capabilities of a receiver
         implementation and indicates the amount of de-packetization
         buffer space in units of bytes that the receiver has available
         for reconstructing the NAL unit decoding order from NAL units
         carried in one or more RTP streams.  A receiver is able to
         handle any RTP stream, and all RTP streams the RTP stream
         depends on, when present, for which the value of the sprop-
         depack-buf-bytes parameter is smaller than or equal to this
         parameter.

         When not present, the value of depack-buf-cap is inferred to
         be equal to 4294967295.  The value of depack-buf-cap MUST be
         an integer in the range of 1 to 4294967295, inclusive.

            Informative note: depack-buf-cap indicates the maximum
            possible size of the de-packetization buffer of the
            receiver only.  When network jitter can occur, an
            appropriately sized jitter buffer has to be available as
            well.

      sprop-segmentation-id:

         This parameter MAY be used to signal the segmentation tools
         present in the bitstream and that can be used for
         parallelization.  The value of sprop-segmentation-id MUST be
         an integer in the range of 0 to 3, inclusive.  When not
         present, the value of sprop-segmentation-id is inferred to be
         equal to 0.

         When sprop-segmentation-id is equal to 0, no information about
         the segmentation tools is provided.  When sprop-segmentation-
         id is equal to 1, it indicates that slices are present in the
         bitstream.  When sprop-segmentation-id is equal to 2, it
         indicates that tiles are present in the bitstream.  When



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         sprop-segmentation-id is equal to 3, it indicates that WPP is
         used in the bitstream.

      sprop-spatial-segmentation-idc:

         A base16 [RFC4648] representation of the syntax element
         min_spatial_segmentation_idc as specified in [HEVC].  This
         parameter MAY be used to describe parallelization capabilities
         of the bitstream.

      dec-parallel-cap:

         This parameter MAY be used to indicate the decoder's
         additional decoding capabilities given the presence of tools
         enabling parallel decoding, such as slices, tiles, and WPP, in
         the bitstream.  The decoding capability of the decoder may
         vary with the setting of the parallel decoding tools present
         in the bitstream, e.g. the size of the tiles that are present
         in a bitstream.  Therefore, multiple capability points may be
         provided, each indicating the minimum required decoding
         capability that is associated with a parallelism requirement,
         which is a requirement on the bitstream that enables parallel
         decoding.

         Each capability point is defined as a combination of 1) a
         parallelism requirement, 2) a profile (determined by profile-
         space and profile-id), 3) a highest level, and 4) a maximum
         processing rate, a maximum picture size, and a maximum video
         bitrate that may be equal to or greater than that determined
         by the highest level.  The parameter's syntax in ABNF
         [RFC5234] is as follows:

            dec-parallel-cap = "dec-parallel-cap={" cap-point *(","
                               cap-point) "}"

            cap-point = ("w" / "t") ":" spatial-seg-idc 1*(";"
                         cap-parameter)

            spatial-seg-idc = 1*4DIGIT ; (1-4095)





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            cap-parameter = tier-flag / level-id / max-lsr
                            / max-lps / max-br

            tier-flag = "tier-flag" EQ ("0" / "1")

            level-id  = "level-id" EQ 1*3DIGIT ; (0-255)

            max-lsr   = "max-lsr" EQ  1*20DIGIT ; (0-
            18,446,744,073,709,551,615)

            max-lps   = "max-lps" EQ 1*10DIGIT ; (0-4,294,967,295)

            max-br    = "max-br"  EQ 1*20DIGIT ; (0-
            18,446,744,073,709,551,615)

            EQ = "="

         The set of capability points expressed by the dec-parallel-cap
         parameter is enclosed in a pair of curly braces ("{}").  Each
         set of two consecutive capability points is separated by a
         comma (',').  Within each capability point, each set of two
         consecutive parameters, and when present, their values, is
         separated by a semicolon (';').

         The profile of all capability points is determined by profile-
         space and profile-id that are outside the dec-parallel-cap
         parameter.

         Each capability point starts with an indication of the
         parallelism requirement, which consists of a parallel tool
         type, which may be equal to 'w' or 't', and a decimal value of
         the spatial-seg-idc parameter.  When the type is 'w', the
         capability point is valid only for H.265 bitstreams with WPP
         in use, i.e. entropy_coding_sync_enabled_flag equal to 1.
         When the type is 't', the capability point is valid only for
         H.265 bitstreams with WPP not in use (i.e.
         entropy_coding_sync_enabled_flag equal to 0).  The capability-
         point is valid only for H.265 bitstreams with
         min_spatial_segmentation_idc equal to or greater than spatial-
         seg-idc.




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         After the parallelism requirement indication, each capability
         point continues with one or more pairs of parameter and value
         in any order for any of the following parameters:

            o tier-flag
            o level-id
            o max-lsr
            o max-lps
            o max-br

         At most one occurrence of each of the above five parameters is
         allowed within each capability point.

         The values of dec-parallel-cap.tier-flag and dec-parallel-
         cap.level-id for a capability point indicate the highest level
         of the capability point.  The values of dec-parallel-cap.max-
         lsr, dec-parallel-cap.max-lps, and dec-parallel-cap.max-br for
         a capability point indicate the maximum processing rate in
         units of luma samples per second, the maximum picture size in
         units of luma samples, and the maximum video bitrate (in units
         of CpbBrVclFactor bits per second for the VCL HRD parameters
         and in units of CpbBrNalFactor bits per second for the NAL HRD
         parameters where CpbBrVclFactor and CpbBrNalFactor are defined
         in Section A.4 of [HEVC]).

         When not present, the value of dec-parallel-cap.tier-flag is
         inferred to be equal to the value of tier-flag outside the
         dec-parallel-cap parameter.  When not present, the value of
         dec-parallel-cap.level-id is inferred to be equal to the value
         of max-recv-level-id outside the dec-parallel-cap parameter.
         When not present, the value of dec-parallel-cap.max-lsr, dec-
         parallel-cap.max-lps, or dec-parallel-cap.max-br is inferred
         to be equal to the value of max-lsr, max-lps, or max-br,
         respectively, outside the dec-parallel-cap parameter.

         The general decoding capability, expressed by the set of
         parameters outside of dec-parallel-cap, is defined as the
         capability point that is determined by the following
         combination of parameters: 1) the parallelism requirement
         corresponding to the value of sprop-segmentation-id equal to 0
         for a bitstream, 2) the profile determined by profile-space,


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         profile-id, profile-compatibility-indicator, and interop-
         constraints, 3) the tier and the highest level determined by
         tier-flag and max-recv-level-id, and 4) the maximum processing
         rate, the maximum picture size, and the maximum video bitrate
         determined by the highest level.  The general decoding
         capability MUST NOT be included as one of the set of
         capability points in the dec-parallel-cap parameter.

         For example, the following parameters express the general
         decoding capability of 720p30 (Level 3.1) plus an additional
         decoding capability of 1080p30 (Level 4) given that the
         spatially largest tile or slice used in the bitstream is equal
         to or less than 1/3 of the picture size:

            a=fmtp:98 level-id=93;dec-parallel-cap={t:8;level-id=120}

         For another example, the following parameters express an
         additional decoding capability of 1080p30, using dec-parallel-
         cap.max-lsr and dec-parallel-cap.max-lps, given that WPP is
         used in the bitstream:

            a=fmtp:98 level-id=93;dec-parallel-cap={w:8;
                        max-lsr=62668800;max-lps=2088960}

            Informative note: When min_spatial_segmentation_idc is
            present in a bitstream and WPP is not used, [HEVC]
            specifies that there is no slice or no tile in the
            bitstream containing more than 4 * PicSizeInSamplesY /
            ( min_spatial_segmentation_idc + 4 ) luma samples.

      include-dph:

         This parameter is used to indicate the capability and
         preference to utilize or include decoded picture hash (DPH)
         SEI messages (See Section D.3.19 of [HEVC]) in the bitstream.
         DPH SEI messages can be used to detect picture corruption so
         the receiver can request picture repair, see Section 8.  The
         value is a comma separated list of hash types that is
         supported or requested to be used, each hash type provided as
         an unsigned integer value (0-255), with the hash types listed
         from most preferred to the least preferred.  Example:



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         "include-dph=0,2", which indicates the capability for MD5
         (most preferred) and Checksum (less preferred).  If the
         parameter is not included or the value contains no hash types,
         then no capability to utilize DPH SEI messages is assumed.
         Note that DPH SEI messages MAY still be included in the
         bitstream even when there is no declaration of capability to
         use them, as in general SEI messages do not affect the
         normative decoding process and decoders are allowed to ignore
         SEI messages.

      Encoding considerations:

         This type is only defined for transfer via RTP (RFC 3550).

      Security considerations:

         See Section 9 of RFC XXXX.

      Public specification:

         Please refer to Section 13 of RFC XXXX.

      Additional information: None

      File extensions: none

      Macintosh file type code: none

      Object identifier or OID: none

      Person & email address to contact for further information:

      Intended usage: COMMON

      Author: See Section 14 of RFC XXXX.

      Change controller:

         IETF Audio/Video Transport Payloads working group delegated
         from the IESG.





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7.2 SDP Parameters

   The receiver MUST ignore any parameter unspecified in this memo.

7.2.1 Mapping of Payload Type Parameters to SDP

   The media type video/H265 string is mapped to fields in the Session
   Description Protocol (SDP) [RFC4566] as follows:

   o  The media name in the "m=" line of SDP MUST be video.

   o  The encoding name in the "a=rtpmap" line of SDP MUST be H265 (the
      media subtype).

   o  The clock rate in the "a=rtpmap" line MUST be 90000.

   o  The OPTIONAL parameters "profile-space", "profile-id", "tier-
      flag", "level-id", "interop-constraints", "profile-compatibility-
      indicator", "sprop-sub-layer-id", "recv-sub-layer-id", "max-recv-
      level-id", "tx-mode", "max-lsr", "max-lps", "max-cpb", "max-dpb",
      "max-br", "max-tr", "max-tc", "max-fps", "sprop-max-don-diff",
      "sprop-depack-buf-nalus", "sprop-depack-buf-bytes", "depack-buf-
      cap", "sprop-segmentation-id", "sprop-spatial-segmentation-idc",
      "dec-parallel-cap", and "include-dph", when present, MUST be
      included in the "a=fmtp" line of SDP.  This parameter is
      expressed as a media type string, in the form of a semicolon
      separated list of parameter=value pairs.

   o  The OPTIONAL parameters "sprop-vps", "sprop-sps", and "sprop-
      pps", when present, MUST be included in the "a=fmtp" line of SDP
      or conveyed using the "fmtp" source attribute as specified in
      section 6.3 of [RFC5576].  For a particular media format (i.e.
      RTP payload type), "sprop-vps" "sprop-sps", or "sprop-pps" MUST
      NOT be both included in the "a=fmtp" line of SDP and conveyed
      using the "fmtp" source attribute.  When included in the "a=fmtp"
      line of SDP, these parameters are expressed as a media type
      string, in the form of a semicolon separated list of
      parameter=value pairs.  When conveyed in the "a=fmtp" line of SDP
      for a particular payload type, the parameters "sprop-vps",
      "sprop-sps", and "sprop-pps" MUST be applied to each SSRC with
      the payload type.  When conveyed using the "fmtp" source



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      attribute, these parameters are only associated with the given
      source and payload type as parts of the "fmtp" source attribute.

          Informative note: Conveyance of "sprop-vps", "sprop-sps", and
          "sprop-pps" using the "fmtp" source attribute allows for out-
          of-band transport of parameter sets in topologies like Topo-
          Video-switch-MCU as specified in [RFC5117].

   An example of media representation in SDP is as follows:

         m=video 49170 RTP/AVP 98
         a=rtpmap:98 H265/90000
         a=fmtp:98 profile-id=1;
                   sprop-vps=<video parameter sets data>

7.2.2 Usage with SDP Offer/Answer Model

   When HEVC is offered over RTP using SDP in an Offer/Answer model
   [RFC3264] for negotiation for unicast usage, the following
   limitations and rules apply:

   o  The parameters identifying a media format configuration for HEVC
      are profile-space, profile-id, tier-flag, level-id, interop-
      constraints, profile-compatibility-indicator, and tx-mode.  These
      media configuration parameters, except level-id, MUST be used
      symmetrically when the answerer does not include recv-sub-layer-
      id in the answer for the media format (payload type) or the
      included recv-sub-layer-id is equal to sprop-sub-layer-id in the
      offer.  The answerer MUST

        1) maintain all configuration parameters with the values
           remaining the same as in the offer for the media format
           (payload type), with the exception that the value of level-
           id is changeable as long as the highest level indicated by
           the answer is not higher than that indicated by the offer;

        2) include in the answer the recv-sub-layer-id parameter, with
           a value less than the sprop-sub-layer-id parameter in the
           offer, for the media format (payload type), and maintain all
           configuration parameters with the values being the same as
           signalled in the sprop-vps for the chosen sub-layer



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           representation, with the exception that the value of level-
           id is changeable as long as the highest level indicated by
           the answer is not higher than the level indicated by the
           sprop-vps in offer for the chosen sub-layer representation;
           or

        3) remove the media format (payload type) completely (when one
           or more of the parameter values are not supported).

          Informative note: The above requirement for symmetric use
          does not apply for level-id, and does not apply for the other
          bitstream or RTP stream properties and capability parameters.

   o  The profile-compatibility-indicator, when offered as sendonly,
      describe bitstream properties.  The answerer MAY accept an RTP
      payload type even if the decoder is not capable of handling the
      profile indicated by the profile-space, profile-id, and interop-
      constraints parameters, but capable of any of the profiles
      indicated by the profile-space, profile-compatibility-indicator,
      and interop-constraints.  However, when the profile-
      compatibility-indicator is used in a recvonly or sendrecv media
      description, the bitstream using this RTP payload type is
      required to conform to all profiles indicated by profile-space,
      profile-compatibility-indicator, and interop-constraints.

   o  To simplify handling and matching of these configurations, the
      same RTP payload type number used in the offer SHOULD also be
      used in the answer, as specified in [RFC3264].

   o  The same RTP payload type number used in the offer MUST be used
      in the answer when the answer includes recv-sub-layer-id.  When
      the answer does not include recv-sub-layer-id, the answer MUST
      NOT contain a payload type number used in the offer unless the
      configuration is exactly the same as in the offer or the
      configuration in the answer only differs from that in the offer
      with a different value of level-id.  The answer MAY contain the
      recv-sub-layer-id parameter if an HEVC bitstream contains
      multiple operation points (using temporal scalability and sub-
      layers) and sprop-vps is included in the offer where information
      of sub-layers are present in the first video parameter set
      contained in sprop-vps.  If the sprop-vps is provided in an


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      offer, an answerer MAY select a particular operation point
      indicated in the first video parameter set contained in sprop-
      vps.  When the answer includes recv-sub-layer-id that is less
      than sprop-sub-layer-id in the offer, all video parameter sets
      contained in the sprop-vps parameter in the SDP answer and all
      video parameter sets sent in-band for either the offerer-to-
      answerer direction or the answerer-to-offerer direction MUST be
      consistent with the first video parameter set in the sprop-vps
      parameter of the offer (see the semantics of sprop-vps on one
      video parameter set being consistent with another video parameter
      set), and the bitstream sent in either direction MUST conform to
      the profile, tier, level, and constraints of the chosen sub-layer
      representation as indicated by the first profile_tier_level( )
      syntax structure in the first video parameter set in the sprop-
      vps parameter of the offer.

          Informative note: When an offerer receives an answer that
          does not include recv-sub-layer-id, it has to compare payload
          types not declared in the offer based on the media type (i.e.
          video/H265) and the above media configuration parameters with
          any payload types it has already declared.  This will enable
          it to determine whether the configuration in question is new
          or if it is equivalent to configuration already offered,
          since a different payload type number may be used in the
          answer.  The ability to perform operation point selection
          enables a receiver to utilize the temporal scalable nature of
          an HEVC bitstream.

   o  The parameters sprop-max-don-diff, sprop-depack-buf-nalus, and
      sprop-depack-buf-bytes describe the properties of an RTP stream,
      and all RTP streams the RTP stream depends on, when present, that
      the offerer or the answerer is sending for the media format
      configuration.  This differs from the normal usage of the
      Offer/Answer parameters: normally such parameters declare the
      properties of the bitstream or RTP stream that the offerer or the
      answerer is able to receive.  When dealing with HEVC, the offerer
      assumes that the answerer will be able to receive media encoded
      using the configuration being offered.

          Informative note:  The above parameters apply for any RTP
          stream and all RTP streams the RTP stream depends on, when


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          present, sent by a declaring entity with the same
          configuration; i.e. they are dependent on their source
          endpoint.  Rather than being bound to the payload type, the
          values may have to be applied to another payload type when
          being sent, as they apply for the configuration.

   o  The capability parameters max-lsr, max-lps, max-cpb, max-dpb,
      max-br, max-tr, and max-tc MAY be used to declare further
      capabilities of the offerer or answerer for receiving.  These
      parameters MUST NOT be present when the direction attribute is
      "sendonly".

   o  The capability parameter max-fps MAY be used to declare lower
      capabilities of the offerer or answerer for receiving.  The
      parameters MUST NOT be present when the direction attribute is
      "sendonly".

   o  The capability parameter dec-parallel-cap MAY be used to declare
      additional decoding capabilities of the offerer or answerer for
      receiving.  Upon receiving such a declaration of a receiver, a
      sender MAY send a bitstream to the receiver utilizing those
      capabilities under the assumption that the bitstream fulfills the
      parallelism requirement.  A bitstream that is sent based on
      choosing a capability point with parallel tool type 'w' from dec-
      parallel-cap MUST have entropy_coding_sync_enabled_flag equal to
      1 and min_spatial_segmentation_idc equal to or larger than dec-
      parallel-cap.spatial-seg-idc of the capability point.  A
      bitstream that is sent based on choosing a capability point with
      parallel tool type 't' from dec-parallel-cap MUST have
      entropy_coding_sync_enabled_flag equal to 0 and
      min_spatial_segmentation_idc equal to or larger than dec-
      parallel-cap.spatial-seg-idc of the capability point.

   o  An offerer has to include the size of the de-packetization
      buffer, sprop-depack-buf-bytes, as well as sprop-max-don-diff and
      sprop-depack-buf-nalus, in the offer for an interleaved HEVC
      bitstream or for the MSM transmission mode.  To enable the
      offerer and answerer to inform each other about their
      capabilities for de-packetization buffering in receiving RTP
      streams, both parties are RECOMMENDED to include depack-buf-cap.
      For interleaved RTP streams or in MSM, it is also RECOMMENDED to


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      consider offering multiple payload types with different buffering
      requirements when the capabilities of the receiver are unknown.

   o  The sprop-vps, sprop-sps, or sprop-pps, when present (included in
      the "a=fmtp" line of SDP or conveyed using the "fmtp" source
      attribute as specified in section 6.3 of [RFC5576]), are used for
      out-of-band transport of the parameter sets (VPS, SPS, or PPS
      respectively).

   o  The answerer MAY use either out-of-band or in-band transport of
      parameter sets for the bitstream it is sending, regardless of
      whether out-of-band parameter sets transport has been used in the
      offerer-to-answerer direction.  Parameter sets included in an
      answer are independent of those parameter sets included in the
      offer, as they are used for decoding two different bitstreams,
      one from the answerer to the offerer and the other in the
      opposite direction.

   o  The capability parameter include-dph MAY be used to declare the
      capability to utilize decoded picture hash SEI messages and which
      types of hashes in any HEVC RTP streams received by the offerer
      or answerer.

   o  The following rules apply to transport of parameter set in the
      offerer-to-answerer direction.

       o An offer MAY include sprop-vps, sprop-sps, and/or sprop-pps.
          If none of these parameters is present in the offer, then
          only in-band transport of parameter sets is used.

       o If the level to use in the offerer-to-answerer direction is
          equal to the default level in the offer, the answerer MUST be
          prepared to use the parameter sets included in sprop-vps,
          sprop-sps, and sprop-pps (either included in the "a=fmtp"
          line of SDP or conveyed using the "fmtp" source attribute)
          for decoding the incoming bitstream, e.g. by passing these
          parameter set NAL units to the video decoder before passing
          any NAL units carried in the RTP streams.  Otherwise, the
          answerer MUST ignore sprop-vps, sprop-sps, and sprop-pps
          (either included in the "a=fmtp" line of SDP or conveyed




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          using the "fmtp" source attribute) and the offerer MUST
          transmit parameter sets in-band.

       o In MSM, the answerer MUST be prepared to use the parameter
          sets out-of-band transmitted for the RTP stream and all RTP
          streams the RTP stream depends on, when present, for decoding
          the incoming bitstream, e.g. by passing these parameter set
          NAL units to the video decoder before passing any NAL units
          carried in the RTP streams.

   o  The following rules apply to transport of parameter set in the
      answerer-to-offerer direction.

       o An answer MAY include sprop-vps, sprop-sps, and/or sprop-pps.
          If none of these parameters is present in the answer, then
          only in-band transport of parameter sets is used.

       o The offerer MUST be prepared to use the parameter sets
          included in sprop-vps, sprop-sps, and sprop-pps (either
          included in the "a=fmtp" line of SDP or conveyed using the
          "fmtp" source attribute) for decoding the incoming bitstream,
          e.g. by passing these parameter set NAL units to the video
          decoder before passing any NAL units carried in the RTP
          streams.

       o In MSM, the offerer MUST be prepared to use the parameter
          sets out-of-band transmitted for the RTP stream and all RTP
          streams the RTP stream depends on, when present, for decoding
          the incoming bitstream, e.g. by passing these parameter set
          NAL units to the video decoder before passing any NAL units
          carried in the RTP streams.

   o  When sprop-vps, sprop-sps, and/or sprop-pps are conveyed using
      the "fmtp" source attribute as specified in section 6.3 of
      [RFC5576], the receiver of the parameters MUST store the
      parameter sets included in sprop-vps, sprop-sps, and/or sprop-pps
      and associate them with the source given as part of the "fmtp"
      source attribute.  Parameter sets associated with one source
      (given as part of the "fmtp" source attribute) MUST only be used
      to decode NAL units conveyed in RTP packets from the same source
      (given as part of the "fmtp" source attribute).  When this


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      mechanism is in use, SSRC collision detection and resolution MUST
      be performed as specified in [RFC5576].

   For bitstreams being delivered over multicast, the following rules
   apply:

   o  The media format configuration is identified by profile-space,
      profile-id, tier-flag, level-id, interop-constraints, profile-
      compatibility-indicator, and tx-mode.  These media format
      configuration parameters, including level-id, MUST be used
      symmetrically; that is, the answerer MUST either maintain all
      configuration parameters or remove the media format (payload
      type) completely.  Note that this implies that the level-id for
      Offer/Answer in multicast is not changeable.

   o  To simplify the handling and matching of these configurations,
      the same RTP payload type number used in the offer SHOULD also be
      used in the answer, as specified in [RFC3264].  An answer MUST
      NOT contain a payload type number used in the offer unless the
      configuration is the same as in the offer.

   o  Parameter sets received MUST be associated with the originating
      source and MUST only be used in decoding the incoming bitstream
      from the same source.

   o  The rules for other parameters are the same as above for unicast
      as long as the three above rules are obeyed.

   Table 1 lists the interpretation of all the parameters that MUST be
   used for the various combinations of offer, answer, and direction
   attributes.  Note that the two columns wherein the recv-sub-layer-id
   parameter is used only apply to answers, whereas the other columns
   apply to both offers and answers.

   Table 1.  Interpretation of parameters for various combinations of
   offers, answers, direction attributes, with and without recv-sub-
   layer-id.  Columns that do not indicate offer or answer apply to
   both.

                                          sendonly --+
            answer: recvonly, recv-sub-layer-id --+  |



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              recvonly w/o recv-sub-layer-id --+  |  |
      answer: sendrecv, recv-sub-layer-id --+  |  |  |
        sendrecv w/o recv-sub-layer-id --+  |  |  |  |
                                         |  |  |  |  |
      profile-space                      C  D  C  D  P
      profile-id                         C  D  C  D  P
      tier-flag                          C  D  C  D  P
      level-id                           D  D  D  D  P
      interop-constraints                C  D  C  D  P
      profile-compatibility-indicator    C  D  C  D  P
      tx-mode                            C  C  C  C  P
      max-recv-level-id                  R  R  R  R  -
      sprop-max-don-diff                 P  P  -  -  P
      sprop- depack-buf-nalus            P  P  -  -  P
      sprop-depack-buf-bytes             P  P  -  -  P
      depack-buf-cap                     R  R  R  R  -
      sprop-segmentation-id              P  P  P  P  P
      sprop-spatial-segmentation-idc     P  P  P  P  P
      max-br                             R  R  R  R  -
      max-cpb                            R  R  R  R  -
      max-dpb                            R  R  R  R  -
      max-lsr                            R  R  R  R  -
      max-lps                            R  R  R  R  -
      max-tr                             R  R  R  R  -
      max-tc                             R  R  R  R  -
      max-fps                            R  R  R  R  -
      sprop-vps                          P  P  -  -  P
      sprop-sps                          P  P  -  -  P
      sprop-pps                          P  P  -  -  P
      sprop-sub-layer-id                 P  P  -  -  P
      recv-sub-layer-id                  X  O  X  O  -
      dec-parallel-cap                   R  R  R  R  -
      include-dph                        R  R  R  R  -



     Legend:

      C: configuration for sending and receiving bitstreams
      D: changable configuration, same as C except possible
         to answer with a different but consistent value (see the


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         semantics of the six parameters related to profile, tier,
         and level on these parameters being consistent)
      P: properties of the bitstream to be sent
      R: receiver capabilities
      O: operation point selection
      X: MUST NOT be present
      -: not usable, when present SHOULD be ignored

   Parameters used for declaring receiver capabilities are in general
   downgradable; i.e. they express the upper limit for a sender's
   possible behavior.  Thus, a sender MAY select to set its encoder
   using only lower/lesser or equal values of these parameters.

   When the answer does not include recv-sub-layer-id that is less than
   the sprop-sub-layer-id in the offer, parameters declaring a
   configuration point are not changeable, with the exception of the
   level-id parameter for unicast usage, and these parameters express
   values a receiver expects to be used and MUST be used verbatim in
   the answer as in the offer.

   When a sender's capabilities are declared with the configuration
   parameters, these parameters express a configuration that is
   acceptable for the sender to receive bitstreams.  In order to
   achieve high interoperability levels, it is often advisable to offer
   multiple alternative configurations.  It is impossible to offer
   multiple configurations in a single payload type.  Thus, when
   multiple configuration offers are made, each offer requires its own
   RTP payload type associated with the offer.  However, it is possible
   to offer multiple operation points using one configuration in a
   single payload type by including sprop-vps in the offer and recv-
   sub-layer-id in the answer.

   A receiver SHOULD understand all media type parameters, even if it
   only supports a subset of the payload format's functionality.  This
   ensures that a receiver is capable of understanding when an offer to
   receive media can be downgraded to what is supported by the receiver
   of the offer.

   An answerer MAY extend the offer with additional media format
   configurations.  However, to enable their usage, in most cases a
   second offer is required from the offerer to provide the bitstream


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   property parameters that the media sender will use.  This also has
   the effect that the offerer has to be able to receive this media
   format configuration, not only to send it.

7.2.3 Usage in Declarative Session Descriptions

   When HEVC over RTP is offered with SDP in a declarative style, as in
   Real Time Streaming Protocol (RTSP) [RFC2326] or Session
   Announcement Protocol (SAP) [RFC2974], the following considerations
   are necessary.

   o  All parameters capable of indicating both bitstream properties
      and receiver capabilities are used to indicate only bitstream
      properties.  For example, in this case, the parameter profile-
      tier-level-id declares the values used by the bitstream, not the
      capabilities for receiving bitstreams.  This results in that the
      following interpretation of the parameters MUST be used:

   Declaring actual configuration or bitstream properties:

     - profile-space
     - profile-id
     - tier-flag
     - level-id
     - interop-constraints
     - profile-compatibility-indicator
     - tx-mode
     - sprop-vps
     - sprop-sps
     - sprop-pps
     - sprop-max-don-diff
     - sprop-depack-buf-nalus
     - sprop-depack-buf-bytes
     - sprop-segmentation-id
     - sprop-spatial-segmentation-idc

   Not usable (when present, they SHOULD be ignored):

     - max-lps
     - max-lsr
     - max-cpb



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     - max-dpb
     - max-br
     - max-tr
     - max-tc
     - max-fps
     - max-recv-level-id
     - depack-buf-cap
     - sprop-sub-layer-id
     - dec-parallel-cap
     - include-dph

   o  A receiver of the SDP is required to support all parameters and
      values of the parameters provided; otherwise, the receiver MUST
      reject (RTSP) or not participate in (SAP) the session.  It falls
      on the creator of the session to use values that are expected to
      be supported by the receiving application.

7.2.4 Parameter Sets Considerations

   When out-of-band transport of parameter sets is used, parameter sets
   MAY still be additionally transported in-band unless explicitly
   disallowed by an application, and some of these additionally in-band
   transported parameter sets may update some of the out-of-band
   transported parameter sets.  Update of a parameter set refers to
   sending of a parameter set of the same type using the same parameter
   set ID but with different values for at least one other parameter of
   the parameter set.

   If MSM is used, the rules on signaling media decoding dependency in
   SDP as defined in [RFC5583] apply.  The rules on "hierarchical or
   layered encoding" with multicast in Section 5.7 of [RFC4566] do not
   apply, i.e. the notation for Connection Data "c=" SHALL NOT be used
   with more than one address.  The order of session dependency is
   given from the RTP stream containing the lowest temporal sub-layer
   to the RTP stream containing the highest temporal sub-layer.

7.2.5 Dependency Signaling in Multi-Stream Mode

   If MSM is used, the rules on signaling media decoding dependency in
   SDP as defined in [RFC5583] apply.  The rules on "hierarchical or
   layered encoding" with multicast in Section 5.7 of [RFC4566] do not


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   apply, i.e. the notation for Connection Data "c=" SHALL NOT be used
   with more than one address.  The order of session dependency is
   given from the RTP stream containing the lowest temporal sub-layer
   to the RTP stream containing the highest temporal sub-layer.

8. Use with Feedback Messages

   As specified in section 6.1 of RFC 4585 [RFC4585], payload Specific
   Feedback messages are identified by the RTCP packet type value PSFB
   (206).  AVPF [RFC4585] defines three payload-specific feedback
   messages and one application layer feedback message, and CCM
   [RFC5104] specifies four payload-specific feedback messages.

   These feedback messages are identified by means of the feedback
   message type (FMT) parameter as follows:

   Assigned in [RFC4585]:

      1:     Picture Loss Indication (PLI)
      2:     Slice Lost Indication (SLI)
      3:     Reference Picture Selection Indication (RPSI)
      15:    Application layer FB message
      31:    reserved for future expansion of the number space

   Assigned in [RFC5104]:

      4:     Full Intra Request (FIR) Command
      5:     Temporal-Spatial Trade-off Request (TSTR)
      6:     Temporal-Spatial Trade-off Notification (TSTN)
      7:     Video Back Channel Message (VBCM)

   Unassigned:

      0:      unassigned
      8-14:   unassigned
      16-30:  unassigned

   The following subsections define the use of the PLI, SLI, RPSI, and
   FIR feedback messages with HEVC.





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8.1 Picture Loss Indication (PLI)

   As specified in RFC 4585 section 6.3.1, the reception of a picture
   loss  indication  by  a  media  sender  indicates  "the  loss  of  an
   undefined amount of coded video data belonging to one or more
   pictures.".  Without having any specific knowledge of the setup of
   the bitstream (such as: use and location of in-band parameter sets,
   non-IDR decoder refresh points, picture structures, and so forth) a
   reaction to the reception of an PLI by an HEVC sender SHOULD be to
   send an IDR picture and relevant parameter sets; potentially with
   sufficient redundancy so to ensure correct reception.  However,
   sometimes information about the bitstream structure is known.  For
   example, state could have been established outside of the mechanisms
   defined in this document that parameter sets are conveyed out of
   band only, and stay static for the duration of the session.  In that
   case, it is obviously unnecessary to send them in-band as a result
   of the reception of a PLI.  Other examples could be devised based on
   a priori knowledge of different aspects of the bitstream structure.
   In all cases, the timing and congestion control mechanisms of RFC
   4585 MUST be observed.

8.2 Slice Loss Indication

   RFC 4585's Slice Loss Indication can be used to indicate, to a
   sender, the loss of a number of Coded Tree Blocks (CTBs) in CTB
   raster scan order of a picture.  In the SLI's Feedback Control
   Indication (FCI) field, the subfield "First" MUST be set to the CTB
   address of the first lost CTB.  Note that the CTB address is in CTB
   raster scan order of a picture.  For the first CTB of a slice
   segment, the CTB address is the value of slice_segment_address when
   present; or 0 when first_slice_segement_in_pic_flag is equal to 1;
   both syntax elements are in the slice segment header.  The subfield
   "Number" MUST be set to the number of consecutive lost CTBs, again
   in CTB raster scan order of a picture.  Note that due to both the
   "First" and "Number" are counted in CTBs in CTB raster scan order,
   of a picture, not in tile scan order (which is the bitstream order
   of CTBs), multiple SLI messages may be needed to report the loss of
   one tile covering multiple CTB rows but less wide than the picture.

   The subfield "PictureID" MUST be set to the 6 least significant bits
   of a binary representation of the value of PicOrderCntVal, as


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   defined in [HEVC], of the picture for which the lost CTBs are
   indicated.    Note  that  for  IDR  pictures  the  syntax  element
   slice_pic_order_cnt_lsb  is  not  present,  but  then  the  value  is
   inferred to be equal to 0.

   As described in RFC 4585, an encoder in a media sender can use this
   information to "clean up" the corrupted picture by sending intra
   information, while observing the constraints described in RFC4585,
   for example with respect to congestion control.  In many cases,
   error tracking is required to identify the corrupted region in the
   receiver's state (reference pictures) because of error import in
   uncorrupted regions of the picture through motion compensation.
   Reference picture selection can also be used to "clean up" the
   corrupted picture, which is usually more efficient and less likely
   to generate congestion than sending intra information.

   In contrast to the video codecs contemplated in RFC 4585 and RFC
   5104, in HEVC, the "macroblock size" is not fixed to 16x16 luma
   samples, but variable.  That, however, does not create a conceptual
   difficulty with SLI, because the setting of the CTB size is a
   sequence-level functionality, and using a slice loss indication
   across coded video sequence boundaries is meaningless as there is no
   prediction across sequence boundaries.  However, a proper use of SLI
   messages is not as straightforward as it was with older, fixed-
   macroblock-sized  video  codecs,  as  the  state  of  the  sequence
   parameter set (where the CTB size is located) has to be taken into
   account when interpreting the "First" subfield in the FCI.

8.3 Use of HEVC with the RPSI Feedback Message

   Feedback based reference picture selection has been shown as a
   powerful tool to stop temporal error propagation for improved error
   resilience [Girod99][Wang05].  In one approach, the decoder side
   tracks errors in the decoded pictures and informs to the encoder
   side that a particular picture that has been decoded relatively
   earlier is correct and still present in the decoded picture buffer
   and requests the encoder to use that correct picture for reference
   when encoding the next picture, so to stop further temporal error
   propagation.  For this approach, the decoder side should use the
   RPSI feedback message.



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   Encoders can encode some long-term reference pictures as specified
   in H.264 or HEVC for purposes described in the previous paragraph
   without the need of a huge decoded picture buffer.  As shown in
   [Wang05], with a flexible reference picture management scheme as in
   H.264 and HEVC, even a decoded picture buffer size of two would work
   for the approach described in the previous paragraph.

   The field "Native RPSI bit string defined per codec" is a base16
   [RFC4648] representation of the 8 bits consisting of 2 most
   significant bits equal to 0 and 6 bits of nuh_layer_id, as defined
   in [HEVC], followed by the 32 bits representing the value of the
   PicOrderCntVal (in network byte order), as defined in [HEVC], for
   the picture that is requested to be used for reference when encoding
   the next picture.

   The use of the RPSI feedback message as positive acknowledgement
   with HEVC is deprecated.  In other words, the RPSI feedback message
   MUST only be used as a reference picture selection request, such
   that it can also be used in multicast.

8.4 Full Intra Request (FIR)

   The purpose of the FIR message is to force an encoder to send an
   independent decoder refresh point as soon as possible (observing,
   for example, the congestion control related constraints set out in
   RFC 5104).

   Upon reception of a FIR, a sender MUST send an IDR picture.
   Parameter sets MUST also be sent, except when there is a priori
   knowledge that the parameter sets have been correctly established.
   (A typical example for that is an understanding between sender and
   receiver, established by means outside this document, that parameter
   sets are exclusively sent out of band.)

9. Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550], and in any applicable RTP profile such as
   RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711] or
   RTP/SAVPF [RFC5124].  However, as "Securing the RTP Protocol



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   Framework: Why RTP Does Not Mandate a Single Media Security
   Solution" [I-D.ietf-avt-srtp-not-mandatory] discusses it is not an
   RTP payload format's responsibility to discuss or mandate what
   solutions are used to meet the basic security goals like
   confidentiality, integrity, and source authenticity for RTP in
   general.  This responsibility lays on anyone using RTP in an
   application.  They can find guidance on available security
   mechanisms and important considerations as discussed in "Options for
   Securing RTP Sessions" [I-D.ietf-avtcore-rtp-security-options].

   The rest of this section discusses the security impacting properties
   of the payload format itself.

   Because the data compression used with this payload format is
   applied end-to-end, any encryption needs to be performed after
   compression.  A potential denial-of-service threat exists for data
   encodings using compression techniques that have non-uniform
   receiver-end computational load.  The attacker can inject
   pathological datagrams into the bitstream that are complex to decode
   and that cause the receiver to be overloaded.  H.265 is particularly
   vulnerable to such attacks, as it is extremely simple to generate
   datagrams containing NAL units that affect the decoding process of
   many future NAL units.  Therefore, the usage of data origin
   authentication and data integrity protection of at least the RTP
   packet is RECOMMENDED, for example, with SRTP [RFC 3711].

   Note that the appropriate mechanism to ensure confidentiality and
   integrity of RTP packets and their payloads is very dependent on the
   application and on the transport and signaling protocols employed.
   Thus, although SRTP is given as an example above, other possible
   choices exist.

   Decoders MUST exercise caution with respect to the handling of user
   data SEI messages, particularly if they contain active elements, and
   MUST restrict their domain of applicability to the presentation
   containing the bitstream.

   End-to-end security with authentication, integrity, or
   confidentiality protection will prevent a MANE from performing
   media-aware operations other than discarding complete packets.  In
   the case of confidentiality protection, it will even be prevented


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   from discarding packets in a media-aware way.  To be allowed to
   perform such operations, a MANE is required to be a trusted entity
   that is included in the security context establishment.

10. Congestion Control

   Congestion control for RTP SHALL be used in accordance with RTP
   [RFC3550] and with any applicable RTP profile, e.g. AVP [RFC 3551].
   If best-effort service is being used, an additional requirement is
   that users of this payload format MUST monitor packet loss to ensure
   that the packet loss rate is within an acceptable range.  Packet
   loss is considered acceptable if a TCP flow across the same network
   path, and experiencing the same network conditions, would achieve an
   average throughput, measured on a reasonable timescale, that is not
   less than all RTP streams combined is achieving.  This condition can
   be satisfied by implementing congestion control mechanisms to adapt
   the transmission rate, the number of layers subscribed for a layered
   multicast session, or by arranging for a receiver to leave the
   session if the loss rate is unacceptably high.

   The bitrate adaptation necessary for obeying the congestion control
   principle is easily achievable when real-time encoding is used, for
   example by adequately tuning the quantization parameter.

   However, when pre-encoded content is being transmitted, bandwidth
   adaptation requires the pre-coded bitstream to be tailored for such
   adaptivity.  The key mechanism available in HEVC is temporal
   scalability.  A media sender can remove NAL units belonging to
   higher temporal sub-layers (i.e. those NAL units with a high value
   of TID) until the sending bitrate drops to an acceptable range.
   HEVC contains mechanisms that allow the lightweight identification
   of switching points in temporal enhancement layers, as discussed in
   Section 1.1.2 of this memo.  An HEVC media sender can send packets
   belonging to NAL units of temporal enhancement layers starting from
   these switching points to probe for available bandwidth and to
   utilized bandwidth that has been shown to be available.

   Above mechanisms generally work within a defined profile and level
   and, therefore, no renegotiation of the channel is required.  Only
   when non-downgradable parameters (such as profile) are required to
   be changed does it become necessary to terminate and restart the RTP


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   stream(s).  This may be accomplished by using different RTP payload
   types.

   MANEs MAY remove certain unusable packets from the RTP stream when
   that RTP stream was damaged due to previous packet losses.  This can
   help reduce the network load in certain special cases.  For example,
   MANES can remove those FUs where the leading FUs belonging to the
   same NAL unit have been lost or those dependent slice segments when
   the leading slice segments belonging to the same slice have been
   lost, because the trailing FUs or dependent slice segments are
   meaningless to most decoders.  MANES can also remove higher temporal
   scalable layers if the outbound transmission (from the MANE's
   viewpoint) experiences congestion.

11. IANA Consideration

   A new media type, as specified in Section 7.1 of this memo, should
   be registered with IANA.

12. Acknowledgements

   Muhammed Coban and Marta Karczewicz are thanked for discussions on
   the specification of the use with feedback messages and other
   aspects in this memo.  Jonathan Lennox and Jill Boyce are thanked
   for their contributions to the PACI design included in this memo.
   Rickard Sjoberg, Arild Fuldseth, Bo Burman, Magnus Westerlund, and
   Tom Kristensen are thanked for their contributions to parallel
   processing related signalling.  Magnus Westerlund, Jonathan Lennox,
   Bernard Aboba, Jonatan Samuelsson, Roni Even, Rickard Sjoberg,
   Sachin Deshpande, Woo Johnman, Mo Zanaty, and Ross Finlayson made
   valuable reviewing comments that led to improvements.

   This document was prepared using 2-Word-v2.0.template.dot.

13. References

13.1 Normative References

   [HEVC]    ITU-T Recommendation H.265, "High efficiency video
             coding", April 2013.




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   [H.264]   ITU-T Recommendation H.264, "Advanced video coding for
             generic audiovisual services", April 2013.

   [RFC5583] Schierl, T. and Wenger, S., "Signaling Media Decoding
             Dependency in the Session Description Protocol (SDP)", RFC
             5583, July 2009.

   [RFC6184] Wang, Y.-K., Even, R., Kristensen, T., and R. Jesup, "RTP
             Payload Format for H.264 Video", RFC 6184, May 2011.

   [RFC6190] Wenger, S., Wang, Y.-K., Schierl, T., and A.
             Eleftheriadis, "RTP Payload Format for Scalable Video
             Coding", RFC 6190, May 2011.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
             with Session Description Protocol (SDP)", RFC 3264, June
             2002.

   [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
             Encodings", RFC 4648, October 2006.

   [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and Jacobson,
             V., "RTP: A Transport Protocol for Real-Time
             Applications", STD 64, RFC 3550, July 2003.

   [RFC4566] Handley, M., Jacobson, V., and Perkins, C., "SDP: Session
             Description Protocol", RFC 4566, July 2006.

   [RFC5576] Lennox, J., Ott, J., and Schierl, T., "Source-Specific
             Media Attributes in the Session Description Protocol", RFC
             5576, June 2009.

   [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and Rey,
             J., "Extended RTP Profile for Real-time Transport Control
             Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July
             2006.





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   [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and Burman, B.,
             "Codec Control Messages in the RTP Audio-Visual Profile
             with Feedback (AVPF)", RFC 5104, February 2008.

13.2 Informative References

   [3GPDASH] 3GPP TS 26.247, "Transparent end-to-end Packet-switched
             Streaming Service (PSS); Progressive Download and Dynamic
             Adaptive Streaming over HTTP (3GP-DASH)", v12.1.0,
             December 2013.

   [3GPPFF]  3GPP TS 26.244, "Transparent end-to-end packet switched
             streaming service (PSS); 3GPP file format (3GP)", v12.20,
             December 2013.

   [Girod99] Girod, B. and Faerber, F., "Feedback-based error control
             for mobile video transmission", Proceedings IEEE, Vol. 87,
             No. 10, pp. 1707-1723, October 1999.

   [HEVC draft v2]
             Draft version 2 of HEVC, "High Efficiency Video Coding
             (HEVC) Range Extensions text specification: Draft 7", JCT-
             VC document JCTVC-Q1005, 17th JCT-VC meeting, 27 March - 4
             April 2014, Valencia, Spain.

   [I-D.ietf-avt-srtp-not-mandatory]
             Perkins, C. and M. Westerlund, "Securing the RTP
             ProtocolFramework: Why RTP Does Not Mandate a Single
             MediaSecurity Solution", draft-ietf-avt-srtp-not-
             mandatory-16 (work in progress), January 2014.

   [I-D.ietf-avtcore-rtp-security-options]
             Westerlund, M. and C. Perkins, "Options for Securing RTP
             Sessions", draft-ietf-avtcore-rtp-security-options-10
             (work in progress), January 2014.

   [I-D.ietf-avtcore-rtp-multi-stream]
             Lennox, J., Westerlund, M., Wu, W., and C. Perkins,
             "Sending Multiple Media Streams in a Single RTP Session",
             draft-ietf-avtcore-rtp-multi-stream-01 (work in progress),
             July 2013.



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   [I-D.ietf-mmusic-sdp-bundle-negotiation]
             Holmberg, C., Alvestrand, H., and C. Jennings,
             "Multiplexing Negotiation Using Session Description
             Protocol (SDP) Port Numbers", draft-ietf-mmusic-sdp-
             bundle-negotiation-05 (work in progress), October 2013.

   [I-D.ietf-avtext-rtp-grouping-taxonomy]
             Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
             Burman, B. "A Taxonomy of Grouping Semantics and
             Mechanisms for Real-Time Transport", draft-ietf-avtext-
             rtp-grouping-taxonomy-01 (work in progress), February
             2014.

   [ISOBMFF] IS0/IEC 14496-12 | 15444-12: "Information technology -
             Coding of audio-visual objects - Part 12: ISO base media
             file format" | "Information technology - JPEG 2000 image
             coding system - Part 12: ISO base media file format",
             2012.

   [JCTVC-J0107]
             Wang, Y.-K., Chen, Y., Joshi, R., and Ramasubramonian, K.,
             "AHG9: On RAP pictures", JCT-VC document JCTVC-L0107, 10th
             JCT-VC meeting, July 2012, Stockholm, Sweden.

   [MPEG2S]  ISO/IEC 13818-1, "Information technology - Generic coding
             of moving pictures and associated audio information:
             Systems", 2013.

   [MPEGDASH] ISO/IEC 23009-1, "Information technology - Dynamic
             adaptive streaming over HTTP (DASH) - Part 1: Media
             presentation description and segment formats", 2012.

   [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
             Correction", RFC 5109, December 2007.

   [Wang05]  Wang, Y.-K., Zhu, C., and Li, H., "Error resilient video
             coding using flexible reference fames", Visual
             Communications and Image Processing 2005 (VCIP 2005), July
             2005, Beijing, China.





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14. Authors' Addresses

   Ye-Kui Wang
   Qualcomm Incorporated
   5775 Morehouse Drive
   San Diego, CA 92121
   USA
   Phone: +1-858-651-8345
   EMail: yekuiw@qti.qualcomm.com

   Yago Sanchez
   Fraunhofer HHI
   Einsteinufer 37
   D-10587 Berlin
   Germany
   Phone: +49-30-31002-227
   Email: yago.sanchez@hhi.fraunhofer.de

   Thomas Schierl
   Fraunhofer HHI
   Einsteinufer 37
   D-10587 Berlin
   Germany
   Phone: +49-30-31002-227
   Email: ts@thomas-schierl.de

   Stephan Wenger
   Vidyo, Inc.
   433 Hackensack Ave., 7th floor
   Hackensack, N.J. 07601
   USA
   Phone: +1-415-713-5473
   EMail: stewe@stewe.org

   Miska M. Hannuksela
   Nokia Corporation
   P.O. Box 1000
   33721 Tampere
   Finland
   Phone: +358-7180-08000



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   EMail: miska.hannuksela@nokia.com















































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