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Versions: (draft-zhao-avtcore-rtp-vvc) 00 01 02 03 04 05

avtcore                                                          S. Zhao
Internet-Draft                                                 S. Wenger
Intended status: Standards Track                                 Tencent
Expires: April 30, 2021                                       Y. Sanchez
                                                          Fraunhofer HHI
                                                        October 27, 2020


          RTP Payload Format for Versatile Video Coding (VVC)
                     draft-ietf-avtcore-rtp-vvc-03

Abstract

   This memo describes an RTP payload format for the video coding
   standard ITU-T Recommendation H.266 and ISO/IEC International
   Standard ISO23090-3, both also known as Versatile Video Coding (VVC)
   and developed by the Joint Video Experts Team (JVET).  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.  The payload
   format has wide applicability in videoconferencing, Internet video
   streaming, and high-bitrate entertainment-quality video, among other
   applications.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 30, 2021.

Copyright Notice

   Copyright (c) 2020 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



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   (https://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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview of the VVC Codec . . . . . . . . . . . . . . . .   3
       1.1.1.  Coding-Tool Features (informative)  . . . . . . . . .   4
       1.1.2.  Systems and Transport Interfaces  . . . . . . . . . .   6
       1.1.3.  Parallel Processing Support (informative) . . . . . .  10
       1.1.4.  NAL Unit Header . . . . . . . . . . . . . . . . . . .  11
     1.2.  Overview of the Payload Format  . . . . . . . . . . . . .  12
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .  12
   3.  Definitions and Abbreviations . . . . . . . . . . . . . . . .  12
     3.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .  12
       3.1.1.  Definitions from the VVC Specification  . . . . . . .  13
       3.1.2.  Definitions Specific to This Memo . . . . . . . . . .  16
     3.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .  16
   4.  RTP Payload Format  . . . . . . . . . . . . . . . . . . . . .  17
     4.1.  RTP Header Usage  . . . . . . . . . . . . . . . . . . . .  18
     4.2.  Payload Header Usage  . . . . . . . . . . . . . . . . . .  19
     4.3.  Payload Structures  . . . . . . . . . . . . . . . . . . .  20
       4.3.1.  Single NAL Unit Packets . . . . . . . . . . . . . . .  20
       4.3.2.  Aggregation Packets (APs) . . . . . . . . . . . . . .  21
       4.3.3.  Fragmentation Units . . . . . . . . . . . . . . . . .  25
     4.4.  Decoding Order Number . . . . . . . . . . . . . . . . . .  28
   5.  Packetization Rules . . . . . . . . . . . . . . . . . . . . .  29
   6.  De-packetization Process  . . . . . . . . . . . . . . . . . .  30
   7.  Payload Format Parameters . . . . . . . . . . . . . . . . . .  32
     7.1.  Media Type Registration . . . . . . . . . . . . . . . . .  32
     7.2.  SDP Parameters  . . . . . . . . . . . . . . . . . . . . .  32
       7.2.1.  Mapping of Payload Type Parameters to SDP . . . . . .  32
       7.2.2.  Usage with SDP Offer/Answer Model . . . . . . . . . .  33
   8.  Use with Feedback Messages  . . . . . . . . . . . . . . . . .  33
     8.1.  Picture Loss Indication (PLI) . . . . . . . . . . . . . .  33
     8.2.  Slice Loss Indication (SLI) . . . . . . . . . . . . . . .  34
     8.3.  Reference Picture Selection Indication (RPSI) . . . . . .  34
     8.4.  Full Intra Request (FIR)  . . . . . . . . . . . . . . . .  34
   9.  Frame Marking . . . . . . . . . . . . . . . . . . . . . . . .  35
     9.1.  Frame Marking Short Extension . . . . . . . . . . . . . .  35
     9.2.  Frame Marking Long Extension  . . . . . . . . . . . . . .  36
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  37
   11. Congestion Control  . . . . . . . . . . . . . . . . . . . . .  38



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   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  39
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  39
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  40
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  40
     14.2.  Informative References . . . . . . . . . . . . . . . . .  42
   Appendix A.  Change History . . . . . . . . . . . . . . . . . . .  43
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  43

1.  Introduction

   The Versatile Video Coding [VVC] specification, formally published as
   both ITU-T Recommendation H.266 and ISO/IEC International Standard
   23090-3 [ISO23090-3], is currently in the ITU-T publication process
   and the ISO/IEC approval process.  [H.266] is reported to provide
   significant coding efficiency gains over H.265 and earlier video
   codec formats.

   This memo specifices an RTP payload format for VVC.  It shares its
   basic design with the NAL (Network Abstraction Layer) unit-based RTP
   payload formats of, H.264 Video Coding [RFC6184], Scalable Video
   Coding (SVC) [RFC6190], High Efficiency Video Coding (HEVC) [RFC7798]
   and their respective predecessors.  With respect to design
   philosophy, security, congestion control, and overall implementation
   complexity, it has similar properties to those earlier payload format
   specifications.  This is a conscious choice, as at least RFC 6184 is
   widely deployed and generally known in the relevant implementer
   communities.  Certain mechanisms known from [RFC6190] were
   incorporated in VVC, as VVC version 1 supports temporal, spatial, and
   signal-to-noise ratio (SNR) scalability.

1.1.  Overview of the VVC Codec

   [VVC] and [HEVC] share a similar hybrid video codec design.  In this
   memo, we provide a very brief overview of those features of VVC that
   are, in some form, addressed by the payload format specified herein.
   Implementers have to read, understand, and apply the ITU- T/ISO/IEC
   specifications pertaining to [VVC] to arrive at interoperable, well-
   performing implementations.

   Conceptually, both [VVC] and [HEVC] include a Video Coding Layer
   (VCL), which is often used to refer to the coding-tool features, and
   a NAL, which is often used to refer to the systems and transport
   interface aspects of the codecs.








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1.1.1.  Coding-Tool Features (informative)

   Coding tool features are described below with occasional reference to
   the coding tool set of [HEVC], which is well known in the community.

   Similar to earlier hybrid-video-coding-based standards, including
   HEVC, the following basic video coding design is employed by VVC.  A
   prediction signal is first formed by either 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, [VVC] includes
   several tools to make the implementation on parallel architectures
   easier.

   Finally, [VVC] includes temporal, spatial, and SNR scalability as
   well as multiview coding support.

   Coding blocks and transform structure

   Among major coding-tool differences between HEVC and VVC, one of the
   important improvements is the more flexible coding tree structure in
   VVC, i.e., multi-type tree.  In addition to quadtree, binary and
   ternary trees are also supported, which contributes significant
   improvement in coding efficiency.  Moreover, the maximum size of
   coding tree unit (CTU) is increased from 64x64 to 128x128.  To
   improve the coding efficiency of chroma signal, luma chroma separated
   trees at CTU level may be employed for intra-slices.  The square
   transforms in HEVC are extended to non-square transforms for
   rectangular blocks resulting from binary and ternary tree splits.
   Besides, [VVC] supports multiple transform sets (MTS), including DCT-
   2, DST-7, and DCT-8 as well as the non-separable secondary transform.
   The transforms used in [VVC] can have different sizes with support
   for larger transform sizes.  For DCT-2, the transform sizes range
   from 2x2 to 64x64, and for DST-7 and DCT-8, the transform sizes range
   from 4x4 to 32x32.  In addition, [VVC] also support sub-block
   transform for both intra and inter coded blocks.  For intra coded
   blocks, intra sub-partitioning (ISP) may be used to allow sub-block
   based intra prediction and transform.  For inter blocks, sub-block
   transform may be used assuming that only a part of an inter-block has
   non-zero transform coefficients.

   Entropy coding

   Similar to HEVC, VVC uses a single entropy-coding engine, which is
   based on context adaptive binary arithmetic coding [CABAC], but with
   the support of multi-window sizes.  The window sizes can be
   initialized differently for different context models.  Due to such a



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   design, it has more efficient adaptation speed and better coding
   efficiency.  A joint chroma residual coding scheme is applied to
   further exploit the correlation between the residuals of two color
   components.  In VVC, different residual coding schemes are applied
   for regular transform coefficients and residual samples generated
   using transform-skip mode.

   In-loop filtering

   VVC has more feature support in loop filters than HEVC.  The
   deblocking filter in VVC is similar to HEVC but operates at a smaller
   grid.  After deblocking and sample adaptive offset (SAO), an adaptive
   loop filter (ALF) may be used.  As a Wiener filter, ALF reduces
   distortion of decoded pictures.  Besides, VVC introduces a new module
   before deblocking called luma mapping with chroma scaling to fully
   utilize the dynamic range of signal so that rate-distortion
   performance of both SDR and HDR content is improved.

   Motion prediction and coding

   Compared to HEVC, [VVC] introduces several improvements in this area.
   First, there is the adaptive motion vector resolution (AMVR), which
   can save bit cost for motion vectors by adaptively signaling motion
   vector resolution.  Then the affine motion compensation is included
   to capture complicated motion like zooming and rotation.  Meanwhile,
   prediction refinement with the optical flow with affine mode (PROF)
   is further deployed to mimic affine motion at the pixel level.
   Thirdly the decoder side motion vector refinement (DMVR) is a method
   to derive MV vector at decoder side based on block matching so that
   fewer bits may be spent on motion vectors.  Bi-directional optical
   flow (BDOF) is a similar method to PROF.  BDOF adds a sample wise
   offset at 4x4 sub-block level that is derived with equations based on
   gradients of the prediction samples and a motion difference relative
   to CU motion vectors.  Furthermore, merge with motion vector
   difference (MMVD) is a special mode, which further signals a limited
   set of motion vector differences on top of merge mode.  In addition
   to MMVD, there are another three types of special merge modes, i.e.,
   sub-block merge, triangle, and combined intra-/inter-prediction
   (CIIP).  Sub- block merge list includes one candidate of sub-block
   temporal motion vector prediction (SbTMVP) and up to four candidates
   of affine motion vectors.  Triangle is based on triangular block
   motion compensation.  CIIP combines intra- and inter- predictions
   with weighting.  Adaptive weighting may be employed with a block-
   level tool called bi-prediction with CU based weighting (BCW) which
   provides more flexibility than in HEVC.

   Intra prediction and intra-coding




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   To capture the diversified local image texture directions with finer
   granularity, [VVC] supports 65 angular directions instead of 33
   directions in HEVC.  The intra mode coding is based on a 6-most -
   probable-mode scheme, and the 6 most probable modes are derived using
   the neighboring intra prediction directions.  In addition, to deal
   with the different distributions of intra prediction angles for
   different block aspect ratios, a wide-angle intra prediction (WAIP)
   scheme is applied in [VVC] by including intra prediction angles
   beyond those present in HEVC.  Unlike HEVC which only allows using
   the most adjacent line of reference samples for intra prediction,
   [VVC] also allows using two further reference lines, as known as
   multi-reference-line (MRL) intra prediction.  The additional
   reference lines can be only used for the 6 most probable intra
   prediction modes.  To capture the strong correlation between
   different colour components, in VVC, a cross-component linear mode
   (CCLM) is utilized which assumes a linear relationship between the
   luma sample values and their associated chroma samples.  For intra
   prediction, [VVC] also applies a position-dependent prediction
   combination (PDPC) for refining the prediction samples closer to the
   intra prediction block boundary.  Matrix-based intra prediction (MIP)
   modes are also used in [VVC] which generates an up to 8x8 intra
   prediction block using a weighted sum of downsampled neighboring
   reference samples, and the weights are hardcoded constants.

   Other coding-tool feature

   [VVC] introduces dependent quantization (DQ) to reduce quantization
   error by state-based switching between two quantizers.

1.1.2.  Systems and Transport Interfaces

   [VVC] inherits the basic systems and transport interfaces designs
   from HEVC and H.264.  These include the NAL-unit-based syntax
   structure, the hierarchical syntax and data unit structure, the
   supplemental enhancement information (SEI) message mechanism, and the
   video buffering model based on the hypothetical reference decoder
   (HRD).  The scalability features of [VVC] are conceptually similar to
   the scalable variant of HEVC known as SHVC.  The hierarchical syntax
   and data unit structure consists of parameter sets at various levels
   (decoder, sequence (pertaining to all), sequence (pertaining to a
   single), picture), picture-level header parameters, slice-level
   header parameters, and lower-level parameters.

   A number of key components that influenced the network abstraction
   layer design of [VVC] as well as this memo are described below

   Decoding Capability Information




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   The decoding capability information includes parameters that stay
   constant for the lifetime of a Video Bitstream, which in IETF terms
   can translate to the lifetime of a session.  Such information
   includes profile, level, and sub-profile information to determine a
   maximum capability interop point that is guaranteed to be never
   exceeded, even if splicing of video sequences occurs within a
   session.  It further includes constraint fields (most of which are
   flags), which can optionally be set to indicate that the video
   bitstream will be constraint in the use of certain features as
   indicated by the values of those fields.  With this, a bitstream can
   be labelled as not using certain tools, which allows among other
   things for resource allocation in a decoder implementation.

   Video parameter set

   TThe ideo parameter set (VPS) pertains to a coded video sequences
   (CVS) of multiple layers covering the same range of access units, and
   includes, among other information decoding dependency expressed as
   information for reference picture list construction of enhancement
   layers.  The VPS provides a "big picture" of a scalable sequence,
   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.  One VPS may be referenced by
   one or more sequence parameter sets.

   Sequence parameter set

   The sequence parameter set (SPS) contains syntax elements pertaining
   to a coded layer video sequence (CLVS), which is a group of pictures
   belonging to the same layer, starting with a random access point, and
   followed by pictures that may depend on each other, until the next
   random access point picture.  In MPGEG-2, the equivalent of a CVS was
   a group of pictures (GOP), which normally started with an I frame and
   was followed by P and B frames.  While more complex in its options of
   random access points, VVC retains this basic concept.  One remarkable
   difference of VVC is that a CLVS may start with a Gradual Decoding
   Refresh (GDR) picture, without requiring presence of traditional
   random access points in the bitstream, such as instantaneous decoding
   refresh (IDR) or clean random access (CRA) pictures.  In many TV-like
   applications, a CVS contains a few hundred milliseconds to a few
   seconds of video.  In video conferencing (without switching MCUs
   involved), a CVS can be as long in duration as the whole session.

   Picture and adaptation parameter set

   The picture parameter set and the adaptation parameter set (PPS and
   APS, respectively) carry information pertaining to zero or more



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   pictures and zero or more slices, respectively.  The PPS contains
   information that is likely to stay constant from picture to picture-
   at least for pictures for a certain type-whereas the APS contains
   information, such as adaptive loop filter coefficients, that are
   likely to change from picture to picture or even within a picture.  A
   single APS is referenced by all slices of the same picture if that
   APS contains information about luma mapping with chroma scaling
   (LMCS) or scaling list.  Different APSs containing ALF parameters can
   be referenced by slices of the same picture.

   Picture Header

   A Picture Header contains information that is common to all slices
   that belong to the same picture.  Being able to send that information
   as a separate NAL unit when pictures are split into several slices
   allows for saving bitrate, compared to repeating the same information
   in all slices.  However, there might be scenarios where low-bitrate
   video is transmitted using a single slice per picture.  Having a
   separate NAL unit to convey that information incurs in an overhead
   for such scenarios.  For such scenarios, the picture header syntax
   structure is directly included in the slice header, instead of in its
   own NAL unit.  The mode of the picture header syntax structure being
   included in its own NAL unit or not can only be switched on/off for
   an entire CLVS, and can only be switched off when in the entire CLVS
   each picture contains only one slice.

   Profile, tier, and level

   The profile, tier and level syntax structures in DCI, VPS and SPS
   contain profile, tier, level information for all layers that refer to
   the DCI, for layers associated with one or more output layer sets
   specified by the VPS, and for any layer that refers to the SPS,
   respectively.

   Sub-Profiles

   Within the VVC specification, a sub-profile is a 32-bit number, coded
   according to ITU-T Rec. T.35, that does not carry a semantics.  It is
   carried in the profile_tier_level structure and hence (potentially)
   present in the DCI, VPS, and SPS.  External registration bodies can
   register a T.35 codepoint with ITU-T registration authorities and
   associate with their registration a description of bitstream
   restrictions beyond the profiles defined by ITU-T and ISO/IEC.  This
   would allow encoder manufacturers to label the bitstreams generated
   by their encoder as complying with such sub-profile.  It is expected
   that upstream standardization organizations (such as: DVB and ATSC),
   as well as walled-garden video services will take advantage of this
   labelling system.  In contrast to "normal" profiles, it is expected



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   that sub-profiles may indicate encoder choices traditionally left
   open in the (decoder- centric) video coding specs, such as GOP
   structures, minimum/maximum QP values, and the mandatory use of
   certain tools or SEI messages.

   Constraint Fields

   The profile_tier_level structure carries a considerable number of
   constraint fields (more of which are flags), which an encoder can use
   to indicate to a decoder that it will not use a certain tool or
   technology.  They were included in reaction to a perceived market
   need for labelling a bitstream as not exercising a certain tool that
   has become commercially unviable.

   Temporal scalability support

      Editor notes: need will update along with VVC new draft in the
      future

   [VVC] includes support of temporal scalability, by inclusion of the
   signaling of TemporalId in the NAL unit header, the restriction that
   pictures of a particular temporal sublayer cannot be used for inter
   prediction reference by pictures of a lower temporal sublayer, 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.

   Picture reference resampling (RPR)

      Editor's notes: to do updated

   Spatial, SNR, and multiview scalability

   [VVC] includes support for spatial, SNR, and multiview scalability.
   Scalable video coding is widely considered to have technical benefits
   and enrich services for various video applications.  Until recently,
   however, the functionality has not been included in the first version
   of specifications of the video codecs.  In VVC, however, all those
   forms of scalability are supported natively through the signaling of
   the layer_id in the NAL unit header, the VPS which associates layers
   with given layer_ids to each other, reference picture selection,
   reference picture resampling for spatial scalability, and a number of
   other mechanisms not relevant for this memo.  Scalability support can
   be implemented in a single decoding "loop" and is widely considered a
   comparatively lightweight operation.

      Spatial Scalability



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         With the existence of Reference Picture Resampling (RPR), in
         the "main" profile of VVC, the additional burden for
         scalability support is just a modification of the high-level
         syntax (HLS).  The inter-layer prediction is employed in a
         scalable system to improve the coding efficiency of the
         enhancement layers.  In addition to the spatial and temporal
         motion-compensated predictions that are available in a single-
         layer codec, the inter-layer prediction in VVC uses the
         possibly resampled video data of the reconstructed reference
         picture from a reference layer to predict the current
         enhancement layer.  The resampling process for inter-layer
         prediction, when used, is performed at the block-level, reusing
         the existing interpolation process for motion compensation in
         single-layer coding.  It means that no additional resampling
         process is needed to support spatial scalability.

      SNR Scalability



         SNR scalability is similar to spatial scalability except that
         the resampling factors are 1:1.  In other words, there is no
         change in resolution, but there is inter-layer prediction.

   SEI Messages

   Supplementary enhancement information (SEI) messages are information
   in the bitstream that do not influence the decoding process as
   specified in the VVC spec, but address issues of representation/
   rendering of the decoded bitstream, label the bitstream for certain
   applications, among other, similar tasks.  The overall concept of SEI
   messages and many of the messages themselves has been inherited from
   the H.264 and HEVC specs.  Except for the SEI messages that affect
   the specification of the hypothetical reference decoder (HRD), other
   SEI messages for use in the VVC environment, which are generally
   useful also in other video coding technologies, are not included in
   the main VVC specification.

1.1.3.  Parallel Processing Support (informative)

   Compared to HEVC, the [VVC] design to support parallelization offers
   numerous improvements.

      Editor notes: udpate on sub-picture/slice/tile is needed following
      new VVC draft






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1.1.4.  NAL Unit Header

   [VVC] maintains the NAL unit concept of HEVC with modifications.  VVC
   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|Z| LayerID   |  Type   | TID |
                     +---------------+---------------+

                   The Structure of the VVC NAL Unit Header.


                                 Figure 1

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

   F: 1 bit

      forbidden_zero_bit.  Required to be zero in VVC.  Note that the
      inclusion of this bit in the NAL unit header was to enable
      transport of [VVC] video over MPEG-2 transport systems (avoidance
      of start code emulations) [MPEG2S].  In the context of this memo
      the value 1 may be used to indicate a syntax violation, e.g., for
      a NAL unit resulted from aggregating a number of fragmented units
      of a NAL unit but missing the last fragment, as described in
      Section TBD.

   Z: 1 bit

      nuh_reserved_zero_bit.  Required to be zero in VVC, and reserved
      for future extensions by ITU-T and ISO/IEC.
      This memo does not overload the "Z" bit for local extensions, as
      a) overloading the "F" bit is sufficient and b) to preserve the
      usefulness of this memo to possible future versions of [VVC].

   LayerId: 6 bits

      nuh_layer_id.  Identifies the layer a NAL unit belongs to, wherein
      a layer may be, e.g., a spatial scalable layer, a quality scalable
      layer .

   Type: 5 bits



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      nal_unit_type.  This field specifies the NAL unit type as defined
      in Table 7-1 of VVC.  For a reference of all currently defined NAL
      unit types and their semantics, please refer to Section 7.4.2.2 in
      [VVC].

   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 [VVC] coded data over RTP [RFC3550]:

   o  Usage of RTP header with this payload format

   o  Packetization of [VVC] coded NAL units into RTP packets using
      three types of payload structures: a single NAL unit packet,
      aggregation packet, and fragment unit

   o  Transmission of [VVC] NAL units of the same bitstream within a
      single RTP stream.

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

   o  Frame-marking mapping [FrameMarking]

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown above.

3.  Definitions and Abbreviations

3.1.  Definitions

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



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3.1.1.  Definitions from the VVC Specification

      Editor notes:

   Access unit (AU): A set of PUs that belong to different layers and
   contain coded pictures associated with the same time for output from
   the DPB.

   Adaptation parameter set (APS): A syntax structure containing syntax
   elements that apply to zero or more slices as determined by zero or
   more syntax elements found in slice headers.

   Bitstream: A sequence of bits, in the form of a NAL unit stream or a
   byte stream, that forms the representation of a sequence of AUs
   forming one or more coded video sequences (CVSs).

   Coded picture: A coded representation of a picture comprising VCL NAL
   units with a particular value of nuh_layer_id within an AU and
   containing all CTUs of the picture.

   Clean random access (CRA) PU: A PU in which the coded picture is a
   CRA picture.

   Clean random access (CRA) picture: An IRAP picture for which each VCL
   NAL unit has nal_unit_type equal to CRA_NUT.

   Coded video sequence (CVS): A sequence of AUs that consists, in
   decoding order, of a CVSS AU, followed by zero or more AUs that are
   not CVSS AUs, including all subsequent AUs up to but not including
   any subsequent AU that is a CVSS AU.

   Coded video sequence start (CVSS) AU: An AU in which there is a PU
   for each layer in the CVS and the coded picture in each PU is a CLVSS
   picture.

   Coded layer video sequence (CLVS): A sequence of PUs with the same
   value of nuh_layer_id that consists, in decoding order, of a CLVSS
   PU, followed by zero or more PUs that are not CLVSS PUs, including
   all subsequent PUs up to but not including any subsequent PU that is
   a CLVSS PU.

   Coded layer video sequence start (CLVSS) PU: A PU in which the coded
   picture is a CLVSS picture.

   Coded layer video sequence start (CLVSS) picture: A coded picture
   that is an IRAP picture with NoOutputBeforeRecoveryFlag equal to 1 or
   a GDR picture with NoOutputBeforeRecoveryFlag equal to 1.




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   Coding tree unit (CTU): A CTB of luma samples, two corresponding CTBs
   of chroma samples of a picture that has three sample arrays, or a CTB
   of samples of a monochrome picture or a picture that is coded using
   three separate colour planes and syntax structures used to code the
   samples.

   Decoding Capability Information (DCI): A syntax structure containing
   syntax elements that apply to the entire bitstream.

   Decoded picture buffer (DPB): A buffer holding decoded pictures for
   reference, output reordering, or output delay specified for the
   hypothetical reference decoder.

   Gradual decoding refresh (GDR) picture: A picture for which each VCL
   NAL unit has nal_unit_type equal to GDR_NUT.

   Instantaneous decoding refresh (IDR) PU: A PU in which the coded
   picture is an IDR picture.

   Instantaneous decoding refresh (IDR) picture: An IRAP picture for
   which each VCL NAL unit has nal_unit_type equal to IDR_W_RADL or
   IDR_N_LP.

   Intra random access point (IRAP) AU: An AU in which there is a PU for
   each layer in the CVS and the coded picture in each PU is an IRAP
   picture.

   Intra random access point (IRAP) PU: A PU in which the coded picture
   is an IRAP picture.

   Intra random access point (IRAP) picture: A coded picture for which
   all VCL NAL units have the same value of nal_unit_type in the range
   of IDR_W_RADL to CRA_NUT, inclusive.

   Layer: A set of VCL NAL units that all have a particular value of
   nuh_layer_id and the associated non-VCL NAL units.

   Network abstraction layer (NAL) unit: A syntax structure containing
   an indication of the type of data to follow and bytes containing that
   data in the form of an RBSP interspersed as necessary with emulation
   prevention bytes.

   Network abstraction layer (NAL) unit stream: A sequence of NAL units.

   Operation point (OP): A temporal subset of an OLS, identified by an
   OLS index and a highest value of TemporalId.





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   Picture parameter set (PPS): A syntax structure containing syntax
   elements that apply to zero or more entire coded pictures as
   determined by a syntax element found in each slice header.

   Picture unit (PU): 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.

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

   Sequence parameter set (SPS): A syntax structure containing syntax
   elements that apply to zero or more entire CLVSs as determined by the
   content of a syntax element found in the PPS referred to by a syntax
   element found in each picture header.

   Slice: An integer number of complete tiles or an integer number of
   consecutive complete CTU rows within a tile of a picture that are
   exclusively contained in a single NAL unit.

   sublayer: 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.

   Subpicture: An rectangular region of one or more slices within a
   picture.

   sublayer representation: A subset of the bitstream consisting of NAL
   units of a particular sublayer and the lower sublayers.

   Tile: A rectangular region of CTUs within a particular tile column
   and a particular tile row in a picture.

   Tile column: A rectangular region of CTUs 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 CTUs having a height specified by
   syntax elements in the picture parameter set and a width equal to the
   width of the picture.

   Video coding layer (VCL) NAL unit: A collective term for coded slice
   NAL units and the subset of NAL units that have reserved values of
   nal_unit_type that are classified as VCL NAL units in this
   Specification.






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3.1.2.  Definitions Specific to This Memo

   Media-Aware Network Element (MANE): A network element, such as a
   middlebox, selective forwarding unit, or application-layer gateway
   that is capable of parsing certain aspects of the RTP payload headers
   or the RTP payload and reacting to their contents.

      Editor Notes: the following informative needs to be updated along
      with frame marking update

      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 Secure RTP
      (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].

   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 [VVC],
   follow the Order of NAL units in the bitstream.

   NAL unit output order: A NAL unit order in which NAL units of
   different access units are in the output order of the decoded
   pictures corresponding to the access units, as specified in [VVC],
   and in which NAL units within an access unit are in their decoding
   order.

   RTP stream: See [RFC7656].  Within the scope of this memo, one RTP
   stream is utilized to transport one or more temporal sublayers.

   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

   AU         Access Unit

   AP         Aggregation Packet

   CTU        Coding Tree Unit



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   CVS        Coded Video Sequence

   DPB        Decoded Picture Buffer

   DCI        Decoding capability information

   DON        Decoding Order Number

   FIR        Full Intra Request

   FU         Fragmentation Unit

   HRD        Hypothetical Reference Decoder

   IDR        Instantaneous Decoding Refresh

   MANE       Media-Aware Network Element

   MTU        Maximum Transfer Unit

   NAL        Network Abstraction Layer

   NALU       Network Abstraction Layer Unit

   PLI        Picture Loss Indication

   PPS        Picture Parameter Set

   RPS        Reference Picture Set

   RPSI       Reference Picture Selection Indication

   SEI        Supplemental Enhancement Information

   SLI        Slice Loss Indication

   SPS        Sequence Parameter Set

   VCL        Video Coding Layer

   VPS        Video Parameter Set

4.  RTP Payload Format








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4.1.  RTP Header Usage

   The format of the RTP header is specified in [RFC3550] (reprinted as
   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
   Section 4.3.2 and Section 4.3.3, respectively.

       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             |
      |                             ....                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        RTP Header According to {{RFC3550}}

                                 Figure 2

   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 of the access unit, carried in the current
      RTP stream.  This is in line with the normal use of the M bit in
      video formats to allow an efficient playout buffer handling.



         Editor notes: The informative note below needs updating once
         the NAL unit type table is stable in the [VVC] spec.



         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



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         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 is
         determined to be the last NAL unit of an access unit if it is
         the last NAL unit of the bitstream.  A NAL unit naluX is also
         determined to be the last NAL unit of an access unit if both
         the following conditions are true: 1) 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 or nal_unit_type
         equal to 19, and 2) all NAL units between naluX and naluY, when
         present, have nal_unit_type in the range of 13 to17, inclusive,
         equal to 20, equal to 23 or equal to 26.

   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.

   Sequence Number (SN): 16 bits

      Set and used in accordance with [RFC3550].

   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
      Annex D of VVC) 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 VVC.

   Synchronization source (SSRC): 32 bits

      Used to identify the source of the RTP packets.  A single SSRC is
      used for all parts of a single bitstream.

4.2.  Payload Header Usage

   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




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   fields (F, Z, LayerId, Type, and TID) as the NAL unit header as shown
   in Section 1.1.4, irrespective of the type of the payload structure.

   The TID value indicates (among other things) the relative importance
   of an RTP packet, for example, because NAL units belonging to higher
   temporal sublayers are not used for the decoding of lower temporal
   sublayers.  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.

      For Discussion: quite possibly something similar can be said for
      the Layer_id in layered coding, but perhaps not in multiview
      coding.  (The relevant part of the spec is relatively new,
      therefore the soft language).  However, for serious layer pruning,
      interpretation of the VPS is required.  We can add language about
      the need for stateful interpretation of LayerID vis-a-vis
      stateless interpretation of TID later.

4.3.  Payload Structures

   Three 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 three 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 4.4.1.

   o  Aggregation Packet (AP): Contains more than one NAL unit within
      one access unit.  This payload structure is specified in
      Section 4.3.2.

   o  Fragmentation Unit (FU): Contains a subset of a single NAL unit.
      This payload structure is specified in Section 4.3.3.

4.3.1.  Single NAL Unit Packets

      Editor notes: its better to add a section to describe DONL and
      sprop-max_don_diff.  sprop-max_don_diff is used but not specified
      as parameters in section 7 are not yet specified.  A value of
      sprop-max_don_diff greater than 0 indicates that the transmission
      order may not correspond to the decoding order and that the DON is
      is included in the payload header.

   A single NAL unit packet contains exactly one NAL unit, and consists
   of a payload header (denoted as PayloadHdr), a conditional 16-bit



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   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        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  The Structure of a Single NAL Unit Packet


                                 Figure 3

   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 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 (sprop-
   max-don-diff is equal to 0), the DONL field MUST NOT be present.

4.3.2.  Aggregation Packets (APs)

   Aggregation Packets (APs) can reduce 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 of 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 included 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.











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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    PayloadHdr (Type=28)       |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                                                               |
    |             two or more aggregation units                     |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   The Structure of an Aggregation Packet


                                 Figure 4

   The fields in the payload header of an AP 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 28.

   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.

   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 FUs
   specified in Section 4.3.3.  APs MUST NOT be nested; i.e., an AP can
   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.





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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               :       DONL (conditional)      |   NALU size   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   NALU size   |                                               |
    +-+-+-+-+-+-+-+-+         NAL unit                              |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           The Structure of the First Aggregation Unit in an AP


                                 Figure 5

   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 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 (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.

   An aggregation unit that is not the first aggregation unit in an AP
   will be followed immediately 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.

















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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               :       NALU size               |   NAL unit    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         The Structure of an Aggregation Unit That Is Not the First
                          Aggregation Unit in an AP


                                 Figure 6

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

     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=28)        |         NALU 1 Size           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          NALU 1 HDR           |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         NALU 1 Data           |
    |                   . . .                                       |
    |                                                               |
    +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  . . .        | NALU 2 Size                   | NALU 2 HDR    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | NALU 2 HDR    |                                               |
    +-+-+-+-+-+-+-+-+              NALU 2 Data                      |
    |                   . . .                                       |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               An Example of an AP Packet Containing
             Two Aggregation Units without the DONL Field


                                 Figure 7





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

     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=28)        |        NALU 1 DONL            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          NALU 1 Size          |            NALU 1 HDR         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                 NALU 1 Data   . . .                           |
    |                                                               |
    +        . . .                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :          NALU 2 Size          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          NALU 2 HDR           |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          NALU 2 Data          |
    |                                                               |
    |        . . .                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   An Example of an AP Containing
                 Two Aggregation Units with the DONL Field


                                 Figure 8

4.3.3.  Fragmentation Units

   Fragmentation Units (FUs) are introduced to enable fragmenting a
   single NAL unit into multiple RTP packets, possibly without
   cooperation or knowledge of the [VVC] 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 can 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=29)        |   FU header   | DONL (cond)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |   DONL (cond) |                                               |
    |-+-+-+-+-+-+-+-+                                               |
    |                         FU payload                            |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          The Structure of an FU


                                 Figure 9

   The fields in the payload header are set as follows.  The Type field
   MUST be equal to 29.  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, an R bit and a 5-bit
   FuType field, as shown in Figure 10.

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

                       The Structure of FU Header

                                 Figure 10

   The semantics of the FU header fields are as follows:

   S: 1 bit





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      When set to 1, 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 0.

   E: 1 bit

      When set to 1, 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 0.

   Reserved: 1 bit

      Placeholder

   FuType: 5 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 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 (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 1 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 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.





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   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 1 to indicate a
   syntax violation.

4.4.  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 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 (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]

         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])



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   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.

      Informative note: When two consecutive NAL units in the NAL unit
      decoding order have different values of AbsDon, 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
      might not forward VCL NAL units of higher sublayers 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.

5.  Packetization Rules

   The following packetization rules apply:

   o  If sprop-max-don-diff is greater than 0, the transmission order of
      NAL units carried in the RTP stream MAY be different than the NAL
      unit decoding order and the NAL unit output order.

   o  A NAL unit of a small size SHOULD be encapsulated in an
      aggregation packet together 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




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      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 pass them to the decoder
   in the NAL unit decoding order.

   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 27,
   inclusive, may be passed to the decoder.  NAL-unit-like structures
   with NAL unit type values in the range of 28 to 31, 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.  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
   hereafter called the de-packetization buffer in this section.
   Receivers should also prepare for transmission delay jitter; that is,



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   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.

   When sprop-max-don-diff is equal to 0, the de-packetization buffer
   size is zero bytes, and the process described in the remainder of
   this paragraph applies.
   The NAL units carried in the single RTP stream are directly passed to
   the decoder in their transmission order, which is identical to their
   decoding order.  When there are several NAL units of the same RTP
   stream with the same NTP timestamp, the order to pass them to the
   decoder is their transmission order.

      Informative note: The mapping between RTP and NTP timestamps is
      conveyed in RTCP SR packets.  In addition, the mechanisms for
      faster media timestamp synchronization discussed in [RFC6051] may
      be used to speed up the acquisition of the RTP-to-wall-clock
      mapping.

   When sprop-max-don-diff is greater than 0, 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.

   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) 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 B become false:





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

7.  Payload Format Parameters

   This section specifies the optional parameters.  A mapping of the
   parameters with Session Description Protocol (SDP) [RFC4556] is also
   provided for applications that use SDP.

7.1.  Media Type Registration

   The receiver MUST ignore any parameter unspecified in this memo.

   Type name:            Video

   Subtype name:         H266

   Required parameters:  none

   Optional parameters:

      Editor's notes: To be added

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/H266 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 H266 (the
      media subtype).

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

   o  OPTIONAL PARAMETERS:

      Editor's notes: To be dicussed here



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7.2.1.1.  SDP Example

   An example of media representation in SDP is as follows:

       m=video 49170 RTP/AVP 98
       a=rtpmap:98 H266/90000
       a=fmtp:98 profile-id=1; sprop-vps=<video parameter sets data>

7.2.2.  Usage with SDP Offer/Answer Model

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

   Placeholder: To add limitations and considerations.

8.  Use with Feedback Messages

   The following subsections define the use of the Picture Loss
   Indication (PLI), Slice Lost Indication (SLI), Reference Picture
   Selection Indication (RPSI), and Full Intra Request (FIR) feedback
   messages with HEVC.  The PLI, SLI, and RPSI messages are defined in
   [RFC4585], and the FIR message is defined in [RFC5104].

8.1.  Picture Loss Indication (PLI)

   As specified in RFC 4585, Section 6.3.1, the reception of a PLI 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-IRAP decoder refresh points,
   picture structures, and so forth), a reaction to the reception of an
   PLI by a [VVC] sender SHOULD be to send an IRAP 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.








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8.2.  Slice Loss Indication (SLI)

   For further study.  Maybe remove as there are no known
   implementations of SDLI in [HEVC] based systems

8.3.  Reference Picture Selection Indication (RPSI)

   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 the encoder side
   that a particular picture that has been decoded relatively earlier is
   correct and still present in the decoded picture buffer; it requests
   the encoder to use that correct picture-availability information when
   encoding the next picture, so to stop further temporal error
   propagation.  For this approach, the decoder side should use the RPSI
   feedback message.

   Encoders can encode some long-term reference pictures as specified in
   [VVC] 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 VVC, even a
   decoded picture buffer size of two picture storage buffers would work
   for the approach described in the previous paragraph.

   The text above is copy-paste from RFC 7798.  If we keep the RPSI
   message, it needs adaptation to the [VVC] syntax.  Doing so shouldn't
   be too hard as the [VVC] reference picture mechanism is not too
   different from the [HEVC] one.

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, while
   observing applicable congestion-control-related constraints, such as
   those set out in [RFC8082]).

   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.








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9.  Frame Marking

   [FrameMarking] provides an extension mechanism for RTP.  The codec-
   agnostic meta-data in the [FrameMarking] header provides valuable
   video frame information.  Its usage with [VVC] is defined in this
   section.  Refer [FrameMarking] for any unspecified fields.  Two
   header extensions are RECOMMENDED:

   o  The short extension for non-scalable streams.

   o  The long extension for scalable streams.

9.1.  Frame Marking Short Extension

   The fields for the short extension, as shown in Figure 11, are used
   as described in the following.

                          0                   1
                          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         |  ID   |  L=0  |S|E|I|D|0 0 0 0|
                         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Short Frame Marking RTP Extension for [VVC]

                                 Figure 11

   The I bit MUST be 1 when the NAL unit type is 7-9 (inclusive),
   otherwise it MUST be 0.

   The D bit MUST be 1 when the syntax element ph_non_ref_pic_flag for a
   picture is equal to 1, otherwise it MUST be 0.

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

   o  The RTP packet is a single NAL unit packet and it is the first VCL
      NAL unit, in decoding order, of a picture.

   o  The RTP packet 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.

   o  The RTP packet is a FU with its S bit equal to 1 and the FU
      payload contains a fragment of the first VCL NAL unit, in decoding
      order, of a picture.





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

   o  The RTP packet is a single NAL unit packet and it is the last VCL
      NAL unit, in decoding order, of a picture.

   o  The RTP packet 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.

   o  The RTP packet is a FU with its E bit equal to 1 and the FU
      payload contains a fragment of the last VCL NAL unit, in decoding
      order, of a picture.

9.2.  Frame Marking Long Extension

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  ID   |  L=2  |S|E|I|D|B| TID |0|0|   LayerID |    TL0PICIDX  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Long Frame Marking RTP Extension for [VVC]

                                 Figure 12

   The fields for the long extension for scalable streams, as shown in
   Figure 12, are used as described in the following.

   The LayerID (6 bits) and TID (3 bits) from the NAL unit header
   Section 1.1.4 are mapped to the generic LID and TID fields in
   [FrameMarking] as shown in Figure 12.

   The I bit MUST be 1 when the NAL unit type is 7-9 (inclusive),
   otherwise it MUST be 0.

   The D bit MUST be 1 when the syntax element ph_non_ref_pic_flag for a
   picture is equal to 1, otherwise it MUST be 0.

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

   o  The RTP packet is a single NAL unit packet and it is the first VCL
      NAL unit, in decoding order, of a picture.

   o  The RTP packet 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.



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   o  The RTP packet is a FU with its S bit equal to 1 and the FU
      payload contains a fragment of the first VCL NAL unit, in decoding
      order, of a picture.

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

   o  The RTP packet is a single NAL unit packet and it is the last VCL
      NAL unit, in decoding order, of a picture.

   o  The RTP packet 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.

   o  The RTP packet is a FU with its E bit equal to 1 and the FU
      payload contains a fragment of the last VCL NAL unit, in decoding
      order, of a picture.

10.  Security Considerations

   The scope of this Security Considerations section is limited to the
   payload format itself and to one feature of [VVC] that may pose a
   particularly serious security risk if implemented naively.  The
   payload format, in isolation, does not form a complete system.
   Implementers are advised to read and understand relevant security-
   related documents, especially those pertaining to RTP (see the
   Security Considerations section in [RFC3550] ), and the security of
   the call-control stack chosen (that may make use of the media type
   registration of this memo).  Implementers should also consider known
   security vulnerabilities of video coding and decoding implementations
   in general and avoid those.

   Within this RTP payload format, and with the exception of the user
   data SEI message as described below, no security threats other than
   those common to RTP payload formats are known.  In other words,
   neither the various media-plane-based mechanisms, nor the signaling
   part of this memo, seems to pose a security risk beyond those common
   to all RTP-based systems.

   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 Framework: Why RTP
   Does Not Mandate a Single Media Security Solution" [RFC7202]
   discusses, it is not an RTP payload format's responsibility to
   discuss or mandate what solutions are used to meet the basic security
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   in general.  This responsibility lays on anyone using RTP in an
   application.  They can find guidance on available security mechanisms
   and important considerations in "Options for Securing RTP Sessions"
   [RFC7201] . 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.  [VVC] 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 [RFC3711] .

   Like HEVC [RFC7798], [VVC] includes a user data Supplemental
   Enhancement Information (SEI) message.  This SEI message allows
   inclusion of an arbitrary bitstring into the video bitstream.  Such a
   bitstring could include JavaScript, machine code, and other active
   content.  [VVC] leaves the handling of this SEI message to the
   receiving system.  In order to avoid harmful side effects the user
   data SEI message, decoder implementations cannot naively trust its
   content.  For example, it would be a bad and insecure implementation
   practice to forward any JavaScript a decoder implementation detects
   to a web browser.  The safest way to deal with user data SEI messages
   is to simply discard them, but that can have negative side effects on
   the quality of experience by the user.

   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 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.

11.  Congestion Control

   Congestion control for RTP SHALL be used in accordance with RTP
   [RFC3550] and with any applicable RTP profile, e.g., AVP [RFC3551].
   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,



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   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 are 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 mechanisms available in [VVC] are temporal scalability, and
   spatial/SNR scalability.  A media sender can remove NAL units
   belonging to higher temporal sublayers (i.e., those NAL units with a
   high value of TID) or higher spatio-SNR layers (as indicated by
   interpreting the VPS) until the sending bitrate drops to an
   acceptable range.

   The mechanisms mentioned above 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 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.

12.  IANA Considerations

   Placeholder

13.  Acknowledgements

   Dr. Byeongdoo Choi is thanked for the video codec related technical
   discussion and other aspects in this memo.  Xin Zhao and Dr. Xiang Li
   are thanked for their contributions on [VVC] specification
   descriptive content.  Spencer Dawkins is thanked for his valuable



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   review comments that led to great improvements of this memo.  Some
   parts of this specification share text with the RTP payload format
   for HEVC [RFC7798].  We thank the authors of that specification for
   their excellent work.

14.  References

14.1.  Normative References

   [H.266]    "ISO/IEC FDIS 23090-3 Information technology --- Coded
              representation of immersive media --- Part 3 - Versatile
              video coding", n.d.,
              <https://www.iso.org/standard/73022.html>.

   [ISO23090-3]
              "ISO/IEC DIS Information technology --- Coded
              representation of immersive media --- Part 3 Versatile
              video codings", n.d.,
              <https://www.iso.org/standard/73022.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <https://www.rfc-editor.org/info/rfc3264>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <https://www.rfc-editor.org/info/rfc3550>.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              DOI 10.17487/RFC3551, July 2003,
              <https://www.rfc-editor.org/info/rfc3551>.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, DOI 10.17487/RFC3711, March 2004,
              <https://www.rfc-editor.org/info/rfc3711>.







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   [RFC4556]  Zhu, L. and B. Tung, "Public Key Cryptography for Initial
              Authentication in Kerberos (PKINIT)", RFC 4556,
              DOI 10.17487/RFC4556, June 2006,
              <https://www.rfc-editor.org/info/rfc4556>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <https://www.rfc-editor.org/info/rfc4566>.

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              DOI 10.17487/RFC4585, July 2006,
              <https://www.rfc-editor.org/info/rfc4585>.

   [RFC5104]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
              "Codec Control Messages in the RTP Audio-Visual Profile
              with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
              February 2008, <https://www.rfc-editor.org/info/rfc5104>.

   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February
              2008, <https://www.rfc-editor.org/info/rfc5124>.

   [RFC7656]  Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
              B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
              for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
              DOI 10.17487/RFC7656, November 2015,
              <https://www.rfc-editor.org/info/rfc7656>.

   [RFC8082]  Wenger, S., Lennox, J., Burman, B., and M. Westerlund,
              "Using Codec Control Messages in the RTP Audio-Visual
              Profile with Feedback with Layered Codecs", RFC 8082,
              DOI 10.17487/RFC8082, March 2017,
              <https://www.rfc-editor.org/info/rfc8082>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [VVC]      "ISO/IEC FDIS 23090-3 Information technology --- Coded
              representation of immersive media --- Part 3 - Versatile
              video coding", n.d.,
              <https://www.iso.org/standard/73022.html>.






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14.2.  Informative References

   [CABAC]    Sole, J, . and . et al, "Transform coefficient coding in
              HEVC, IEEE Transactions on Circuts and Systems for Video
              Technology", DOI 10.1109/TCSVT.2012.2223055, December
              2012.

   [FrameMarking]
              Berger, E, ., Nandakumar, S, ., and . Zanaty M, "Frame
              Marking RTP Header Extension", Work in Progress draft-
              berger-avtext-framemarking , 2015.

   [Girod99]  Girod, B, . and . et al, "Feedback-based error control for
              mobile video transmission, Proceedings of the IEEE",
              DOI 110.1109/5.790632, October 1999.

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

   [MPEG2S]   IS0/IEC, ., "Information technology - Generic coding
              ofmoving pictures and associated audio information - Part
              1:Systems, ISO International Standard 13818-1", 2013.

   [RFC6051]  Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP
              Flows", RFC 6051, DOI 10.17487/RFC6051, November 2010,
              <https://www.rfc-editor.org/info/rfc6051>.

   [RFC6184]  Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP
              Payload Format for H.264 Video", RFC 6184,
              DOI 10.17487/RFC6184, May 2011,
              <https://www.rfc-editor.org/info/rfc6184>.

   [RFC6190]  Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis,
              "RTP Payload Format for Scalable Video Coding", RFC 6190,
              DOI 10.17487/RFC6190, May 2011,
              <https://www.rfc-editor.org/info/rfc6190>.

   [RFC7201]  Westerlund, M. and C. Perkins, "Options for Securing RTP
              Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014,
              <https://www.rfc-editor.org/info/rfc7201>.

   [RFC7202]  Perkins, C. and M. Westerlund, "Securing the RTP
              Framework: Why RTP Does Not Mandate a Single Media
              Security Solution", RFC 7202, DOI 10.17487/RFC7202, April
              2014, <https://www.rfc-editor.org/info/rfc7202>.






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   [RFC7798]  Wang, Y., Sanchez, Y., Schierl, T., Wenger, S., and M.
              Hannuksela, "RTP Payload Format for High Efficiency Video
              Coding (HEVC)", RFC 7798, DOI 10.17487/RFC7798, March
              2016, <https://www.rfc-editor.org/info/rfc7798>.

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

Appendix A.  Change History

   draft-zhao-payload-rtp-vvc-00 ........ initial version

   draft-zhao-payload-rtp-vvc-01 ........ editorial clarifications and
   corrections

   draft-ietf-payload-rtp-vvc-00 ........ initial WG draft

   draft-ietf-payload-rtp-vvc-01 ........ VVC specification update

   draft-ietf-payload-rtp-vvc-02 ........ VVC specification update

   draft-ietf-payload-rtp-vvc-03 ........ VVC coding tool introduction
   update

Authors' Addresses

   Shuai Zhao
   Tencent
   2747 Park Blvd
   Palo Alto  94588
   USA

   Email: shuai.zhao@ieee.org


   Stephan Wenger
   Tencent
   2747 Park Blvd
   Palo Alto  94588

   Email: stewe@stewe.org








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   Yago Sanchez
   Fraunhofer HHI
   Einsteinufer 37
   Berlin  10587
   Germany

   Email: yago.sanchez@hhi.fraunhofer.de












































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