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Versions: (draft-kristensen-avt-rtp-h264-rcdo) 00 01 02 03 04 05 06 07 08 RFC 6185

Audio/Video Transport WG                                   T. Kristensen
Internet-Draft                                                  P. Luthi
Intended status: Standards Track                                TANDBERG
Expires: August 27, 2010                               February 23, 2010


                RTP Payload Format for H.264 RCDO Video
                    draft-ietf-avt-rtp-h264-rcdo-05

Abstract

   This document describes an RTP Payload format for the Reduced-
   Complexity Decoding Operation (RCDO) for H.264 Baseline profile
   bitstreams, as specified in ITU-T Recommendation H.241.  RCDO reduces
   the decoding cost and resource consumption of the video processing.
   The RCDO RTP Payload format is based on the H.264 RTP Payload format.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 27, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
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   it for publication as an RFC or to translate it into languages other
   than English.

































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions, Definitions and Acronyms  . . . . . . . . . . . .  4
   3.  Media Format Background  . . . . . . . . . . . . . . . . . . .  4
   4.  Payload Format . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Congestion Control Considerations  . . . . . . . . . . . . . .  5
   6.  Payload Format Parameters  . . . . . . . . . . . . . . . . . .  5
     6.1.  Media Type Definition  . . . . . . . . . . . . . . . . . .  5
   7.  Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . . . 21
     7.1.  Offer/Answer Considerations  . . . . . . . . . . . . . . . 21
     7.2.  Declarative SDP Considerations . . . . . . . . . . . . . . 21
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 21
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
     11.2. Informative references . . . . . . . . . . . . . . . . . . 23
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
































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1.  Introduction

   ITU-T Recommendation H.241 [5] specifies a reduced-complexity
   decoding operation (RCDO) for use with H.264 [4] Baseline profile
   bitstreams.  It also specifies a bitstream constraint associated with
   RCDO and a mechanism for signalling RCDO within the bitstream.  The
   RCDO signalling indicates that the bitstream conforms to the
   bitstream constraint and that the decoder shall apply the RCDO
   decoding process to the bitstream.

   RCDO for H.264 offers a solution to support higher resolutions at the
   same high framerates used in current implementations.  This is
   achieved by reducing the processing requirements and thus the
   decoding cost/resource consumption of the video processing.


2.  Conventions, Definitions and Acronyms

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [1].

   RFC-editor note: RFC XXXX is to be replaced by the RFC number this
   specification recieves when published.


3.  Media Format Background

   The Reduced-Complexity Decoding Operation (RCDO) for H.264 Baseline
   profile bitstreams is specified in Annex B of H.241 [5].  RCDO is
   specified as a separate H.264 mode, and is distinct from any profile
   defined in H.264.  An RCDO bitstream obey to all the constraints of
   the Baseline profile.

   The media format is based on the H.264 RTP Payload format as
   specified in RFC3984bis [3].  Therefore, RFC3984bis constitutes the
   basis for this document and is referred to several times.

   In order to signal H.264 additional modes, Table 9f of H.241 [5]
   specifies an AdditionalModesSupported parameter.  Currently, the only
   additional mode defined is RCDO.

      Informative note: Other additional modes may be defined in the
      future.  H.264 additional modes may or may not be distinct from
      the Profiles in H.264.

   A separate media subtype, named H264-RCDO, is defined to ensure
   backward compatibility with deployed implementations of H.264.



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4.  Payload Format

   The payload format defined in Section 5 of RFC3984bis [3] SHALL be
   used.  This includes the RTP header usage and the payload format in
   RFC3984bis.  Examples of typical RTP packets can be found in
   RFC3984bis.


5.  Congestion Control Considerations

   Congestion control for RTP SHALL be used in accordance with RFC 3550
   [6], and with any applicable RTP profile; e.g., RFC 3551 [7].  If
   best-effort service is being used, users of this payload format SHALL
   monitor packet loss to ensure that the packet loss rate is within
   acceptable parameters.


6.  Payload Format Parameters

   This RTP payload format is identified using the H264-RCDO media
   subtype which is registered in accordance with RFC 4855 [8] and using
   the template of RFC 4288 [10].

6.1.  Media Type Definition

      Informative note: The media subtype definition for H264-RCDO is
      based on the definition of the H264 media subtype as specified in
      Section 8.1 of RFC3984bis [3].  Except for the profile-level-id
      parameter where new semantics are specified below, the optional
      parameters are copied verbatim from RFC3984bis [3] for
      completeness in the IANA registration.

   The media subtype for RCDO for H.264 is allocated from the IETF tree.

   The receiver MUST ignore any unspecified parameter.

   Type name: video

   Subtype name: H264-RCDO

   Required parameters:

   rate:  Indicates the RTP timestamp clock rate.  The rate value MUST
      be 90000.

   Optional parameters:





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   profile-level-id:  A base16 RFC 3548 [9] (hexadecimal) representation
      of the following three bytes in the sequence parameter set NAL
      unit specified in H.264 [4]: 1) profile_idc, 2) a byte herein
      referred to as profile-iop, composed of the values of
      constraint_set0_flag, constraint_set1_flag, constraint_set2_flag,
      constraint_set3_flag, and reserved_zero_4bits in bit-significance
      order, starting from the most significant bit, and 3) level_idc.
      Note that reserved_zero_4bits is required to be equal to 0 in
      H.264 [4], but other values for it may be specified in the future
      by ITU-T or ISO/IEC.

      The profile-level-id parameter indicates the default sub-profile,
      i.e. the subset of coding tools that may have been used to
      generate the stream or that the receiver supports, and the default
      level of the stream or the receiver supports.

      RCDO is distinct from any profile, this implies that the profile
      value 0 (no profile) and the profile_idc byte of the profile-
      level-id parameter are equal to 0.  An RCDO bitstream MUST obey to
      all the constraints of the Baseline profile.  Therefore, only
      constraint_set0_flag is equal to 1 in the profile-iop part of the
      profile-level-id parameter, the remaining bits are set to 0.

      If the profile-level-id parameter is used to indicate properties
      of a NAL unit stream, it indicates that, to decode the stream, the
      lowest level the decoder has to support is the default level.
      If the profile-level-id parameter is used for capability exchange
      or session setup procedure, and if max-recv-level is not present,
      the default level from profile-level-id indicates the highest
      level the codec wishes to support.  If max-recv-level is present
      it indicates the highest level the codec supports for receiving.
      For either receiving or sending, all levels that are lower than
      the highest level supported MUST also be supported.

      For example, if a codec supports level 1.3, the profile-level-id
      becomes 00800d, in which 00 indicates the "no profile" value, 80
      indicates the constraints of the Baseline profile and 0d indicates
      level 1.3.  When level 2.1 is supported, the profile-level-id
      becomes 008015.

      If no profile-level-id is present, level 1 MUST be implied, i.e.
      equivalent to profile-level-id 00800a.

   max-recv-level:  This parameter MAY be used to indicate the highest
      level a receiver supports when the highest level is higher than
      the default level (the level indicated by profile-level-id).  The
      value of max-recv-level is a base16 (hexadecimal) representation
      of the two bytes after the syntax element profile_idc in the



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      sequence parameter set NAL unit specified in H.264 [4]: profile-
      iop (as defined above) and level_idc.  If (the level_idc byte of
      max-recv-level is equal to 11 and bit 4 of the profile-iop byte of
      max-recv-level is equal to 1) or (the level_idc byte of max-recv-
      level is equal to 9 and bit 4 of the profile-iop byte of max-recv-
      level is equal to 0), the highest level the receiver supports is
      level 1b.  Otherwise, the highest level the receiver supports is
      equal to the level_idc byte of max-recv-level divided by 10.

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

   max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br:  These
      parameters MAY be used to signal the capabilities of a receiver
      implementation.  These parameters MUST NOT be used for any other
      purpose.  The highest level conveyed in the value of the profile-
      level-id parameter or the max-recv-level parameter MUST be such
      that the receiver is fully capable of supporting. max-mbps, max-
      smbps, max-fs, max-cpb, max-dpb, and max-br MAY be used to
      indicate capabilities of the receiver that extend the required
      capabilities of the signaled highest level, as specified below.

      When more than one parameter from the set (max-mbps, max-smbps ,
      max-fs, max-cpb, max-dpb, max-br) is present, the receiver MUST
      support all signaled capabilities simultaneously.  For example, if
      both max-mbps and max-br are present, the signaled highest level
      with the extension of both the frame rate and bit rate is
      supported.  That is, the receiver is able to decode NAL unit
      streams in which the macroblock processing rate is up to max-mbps
      (inclusive), the bit rate is up to max-br (inclusive), the coded
      picture buffer size is derived as specified in the semantics of
      the max-br parameter below, and other properties comply with the
      highest level specified in the value of the profile-level-id
      parameter or the max-recv-level parameter.

      If a receiver can support all the properties of level A, the
      highest level specified in the value of the profile-level-id
      parameter or the max-recv-level parameter MUST be level A (i.e.
      MUST NOT be lower than level A).  In other words, a receiver MUST
      NOT signal values of max-mbps, max-fs, max-cpb, max-dpb, and
      max-br that taken together meet the requirements of a higher level
      compared to the highest level specified in the value of the
      profile-level-id parameter or the max-recv- level parameter.

         Informative note: When the OPTIONAL media type parameters are
         used to signal the properties of a NAL unit stream, max-mbps,
         max-smbps, max-fs, max-cpb, max-dpb, and max-br are not
         present, and the value of profile-level-id must always be such



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         that the NAL unit stream complies fully with the specified
         profile and level.

   max-mbps:  The value of max-mbps is an integer indicating the maximum
      macroblock processing rate in units of macroblocks per second.
      The max-mbps parameter signals that the receiver is capable of
      decoding video at a higher rate than is required by the signaled
      highest level conveyed in the value of the profile-level-id
      parameter or the max-recv-level parameter.  When max-mbps is
      signaled, the receiver MUST be able to decode NAL unit streams
      that conform to the signaled highestlevel, with the exception that
      the MaxMBPS value in Table A-1 of H.264 [4] for the signaled
      highest level is replaced with the value of max-mbps.  The value
      of max-mbps MUST be greater than or equal to the value of MaxMBPS
      given in Table A-1 of H.264 [4] for the highest level.  Senders
      MAY use this knowledge to send pictures of a given size at a
      higher picture rate than is indicated in the signaled highest
      level.

   max-smbps:  The value of max-smbps is an integer indicating the
      maximum static macroblock processing rate in units of static
      macroblocks per second, under the hypothetical assumption that all
      macroblocks are static macroblocks.  When max-smbps is signalled
      the MaxMBPS value in Table A-1 of H.264 [4] should be replaced
      with the result of the following computation:

      o If the parameter max-mbps is signalled, set a variable
      MaxMacroblocksPerSecond to the value of max-mbps.  Otherwise, set
      MaxMacroblocksPerSecond equal to the value of MaxMBPS in Table A-1
      H.264 [4] for the highest level.

      o Set a variable P_non-static to the proportion of non- static
      macroblocks in picture n.

      o Set a variable P_static to the proportion of static macroblocks
      in picture n.

      o The value of MaxMBPS in Table A-1 of H.264 [4] should be
      considered by the encoder to be equal to:

         MaxMacroblocksPerSecond * max-smbps / (P_non-static * max-smbps
         + P_static * MaxMacroblocksPerSecond)

      The encoder should recompute this value for each picture.  The
      value of max-smbps MUST be greater than the value of MaxMBPS given
      in Table A-1 of H.264 [4] for the highest level.  Senders MAY use
      this knowledge to send pictures of a given size at a higher
      picture rate than is indicated in the signaled highest level.



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   max-fs:  The value of max-fs is an integer indicating the maximum
      frame size in units of macroblocks.  The max-fs parameter signals
      that the receiver is capable of decoding larger picture sizes than
      are required by the signaled highest level conveyed in the value
      of the profile-level-id parameter or the max-recv-level parameter.
      When max-fs is signaled, the receiver MUST be able to decode NAL
      unit streams that conform to the signaled highest level, with the
      exception that the MaxFS value in Table A-1 of H.264 [4] for the
      signaled highest level is replaced with the value of max-fs.  The
      value of max-fs MUST be greater than or equal to the value of
      MaxFS given in Table A-1 of H.264 [4] for the highest level.
      Senders MAY use this knowledge to send larger pictures at a
      proportionally lower frame rate than is indicated in the signaled
      highest level.

   max-cpb:  The value of max-cpb is an integer indicating the maximum
      coded picture buffer size in units of 1000 bits for the VCL HRD
      parameters (see A.3.1 item i of H.264 [4]) and in units of 1200
      bits for the NAL HRD parameters (see A.3.1 item j of H.264 [4]).
      The max-cpb parameter signals that the receiver has more memory
      than the minimum amount of coded picture buffer memory required by
      the signaled highest level conveyed in the value of the profile-
      level-id parameter or the max-recv-level parameter.  When max-cpb
      is signaled, the receiver MUST be able to decode NAL unit streams
      that conform to the signaled highest level, with the exception
      that the MaxCPB value in Table A-1 of H.264 [4] for the signaled
      highest level is replaced with the value of max-cpb.  The value of
      max-cpb MUST be greater than or equal to the value of MaxCPB given
      in Table A-1 of H.264 [4] for the highest level.  Senders MAY use
      this knowledge to construct coded video streams with greater
      variation of bit rate than can be achieved with the MaxCPB value
      in Table A-1 of H.264 [4].

         Informative note: The coded picture buffer is used in the
         hypothetical reference decoder (Annex C) of H.264.  The use of
         the hypothetical reference decoder is recommended in H.264
         encoders to verify that the produced bitstream conforms to the
         standard and to control the output bitrate.  Thus, the coded
         picture buffer is conceptually independent of any other
         potential buffers in the receiver, including de-interleaving
         and de-jitter buffers.  The coded picture buffer need not be
         implemented in decoders as specified in Annex C of H.264, but
         rather standard-compliant decoders can have any buffering
         arrangements provided that they can decode standard- compliant
         bitstreams.  Thus, in practice, the input buffer for video
         decoder can be integrated with de- interleaving and de-jitter
         buffers of the receiver.



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   max-dpb:  The value of max-dpb is an integer indicating the maximum
      decoded picture buffer size in units of 1024 bytes.  The max-dpb
      parameter signals that the receiver has more memory than the
      minimum amount of decoded picture buffer memory required by the
      signaled highest level conveyed in the value of the
      profile-level-id parameter or the max-recv-level parameter.  When
      max-dpb is signaled, the receiver MUST be able to decode NAL unit
      streams that conform to the signaled highest level, with the
      exception that the MaxDPB value in Table A-1 of H.264 [4] for the
      signaled highest level is replaced with the value of max-dpb.
      Consequently, a receiver that signals max-dpb MUST be capable of
      storing the following number of decoded frames, complementary
      field pairs, and non- paired fields in its decoded picture buffer:


         Min(1024 * max-dpb / ( PicWidthInMbs * FrameHeightInMbs * 256 *
         ChromaFormatFactor ), 16)

      PicWidthInMbs, FrameHeightInMbs, and ChromaFormatFactor are
      defined in H.264 [4].

      The value of max-dpb MUST be greater than or equal to the value of
      MaxDPB given in Table A-1 of H.264 [4] for the highest level.
      Senders MAY use this knowledge to construct coded video streams
      with improved compression.

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

   max-br:  The value of max-br is an integer indicating the maximum
      video bit rate in units of 1000 bits per second for the VCL HRD
      parameters (see A.3.1 item i of H.264 [4]) and in units of 1200
      bits per second for the NAL HRD parameters (see A.3.1 item j of
      H.264 [4]).

      The max-br parameter signals that the video decoder of the
      receiver is capable of decoding video at a higher bit rate than is
      required by the signaled highest level conveyed in the value of
      the profile-level-id parameter or the max-recv- level parameter.






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

      o The value of max-br replaces the MaxBR value in Table A-1 of
      H.264 [4] for the highest level.

      o When the max-cpb parameter is not present, the result of the
      following formula replaces the value of MaxCPB in Table A-1 of
      H.264 [4]: (MaxCPB of the signaled level) * max-br / (MaxBR of the
      signaled highest level).

      For example, if a receiver signals capability for Level 1.2 with
      max-br equal to 1550, this indicates a maximum video bitrate of
      1550 kbits/sec for VCL HRD parameters, a maximum video bitrate of
      1860 kbits/sec for NAL HRD parameters, and a CPB size of 4036458
      bits (1550000 / 384000 * 1000 * 1000).

      The value of max-br MUST be greater than or equal to the value
      MaxBR given in Table A-1 of H.264 [4] for the signaled highest
      level.

      Senders MAY use this knowledge to send higher bitrate video as
      allowed in the level definition of Annex A of H.264, to achieve
      improved video quality.

         Informative note: This parameter was added primarily to
         complement a similar codepoint in the ITU-T Recommendation
         H.245, so as to facilitate signaling gateway designs.  No
         assumption can be made from the value of this parameter that
         the network is capable of handling such bit rates at any given
         time.  In particular, no conclusion can be drawn that the
         signaled bit rate is possible under congestion control
         constraints.

   redundant-pic-cap:  This parameter signals the capabilities of a
      receiver implementation.  When equal to 0, the parameter indicates
      that the receiver makes no attempt to use redundant coded pictures
      to correct incorrectly decoded primary coded pictures.  When equal
      to 0, the receiver is not capable of using redundant slices;
      therefore, a sender SHOULD avoid sending redundant slices to save
      bandwidth.  When equal to 1, the receiver is capable of decoding
      any such redundant slice that covers a corrupted area in a primary
      decoded picture (at least partly), and therefore a sender MAY send
      redundant slices.  When the parameter is not present, then a value
      of 0 MUST be used for redundant-pic-cap.  When present, the value



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      of redundant-pic-cap MUST be either 0 or 1.

      When the profile-level-id parameter is present in the same
      signaling as the redundant-pic-cap parameter, and the profile
      indicated in profile-level-id is such that it disallows the use of
      redundant coded pictures (e.g., Main Profile), the value of
      redundant-pic-cap MUST be equal to 0.  When a receiver indicates
      redundant-pic-cap equal to 0, the received stream SHOULD NOT
      contain redundant coded pictures.

         Informative note: Even if redundant-pic-cap is equal to 0, the
         decoder is able to ignore redundant codec pictures provided
         that the decoder supports such a profile (Baseline, Extended)
         in which redundant coded pictures are allowed.


         Informative note: Even if redundant-pic-cap is equal to 1, the
         receiver may also choose other error concealment strategies to
         replace or complement decoding of redundant slices.

   sprop-parameter-sets:  This parameter MAY be used to convey any
      sequence and picture parameter set NAL units (herein referred to
      as the initial parameter set NAL units) that can be placed in the
      NAL unit stream to precede any other NAL units in decoding order.
      The parameter MUST NOT be used to indicate codec capability in any
      capability exchange procedure.  The value of the parameter is a
      comma (',') separated list of base64 RFC 3548 [9] representations
      of parameter set NAL units as specified in sections 7.3.2.1 and
      7.3.2.2 of H.264 [4].  Note that the number of bytes in a
      parameter set NAL unit is typically less than 10, but a picture
      parameter set NAL unit can contain several hundreds of bytes.


         Informative note: When several payload types are offered in the
         SDP Offer/Answer model, each with its own sprop- parameter-sets
         parameter, then the receiver cannot assume that those parameter
         sets do not use conflicting storage locations (i.e., identical
         values of parameter set identifiers).  Therefore, a receiver
         should buffer all sprop-parameter-sets and make them available
         to the decoder instance that decodes a certain payload type.

      The "sprop-parameter-sets" parameter MUST only contain parameter
      sets that are conforming to the profile-level-id, i.e., the subset
      of coding tools indicated by any of the parameter sets MUST be
      equal to the default sub-profile, and the level indicated by any
      of the parameter sets MUST be equal to the default level.





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   sprop-level-parameter-sets:  This parameter MAY be used to convey any
      sequence and picture parameter set NAL units (herein referred to
      as the initial parameter set NAL units) that can be placed in the
      NAL unit stream to precede any other NAL units in decoding order
      and that are associated with one or more levels different than the
      default level.  The parameter MUST NOT be used to indicate codec
      capability in any capability exchange procedure.

      The sprop-level-parameter-sets parameter contains parameter sets
      for one or more levels which are different than the default level.
      All parameter sets associated with one level are clustered and
      prefixed with a three-byte field which has the same syntax as
      profile-level-id.  This enables the receiver to install the
      parameter sets for one level and discard the rest.  The three-byte
      field is named PLId, and all parameter sets associated with one
      level are named PSL, which has the same syntax as sprop-parameter-
      sets.  Parameter sets for each level are represented in the form
      of PLId:PSL, i.e., PLId followed by a colon (':') and the base64
      RFC 3548 [9] representation of the initial parameter set NAL units
      for the level.  Each pair of PLId:PSL is also separated by a
      colon.  Note that a PSL can contain multiple parameter sets for
      that level, separated with commas (',').

      The subset of coding tools indicated by each PLId field MUST be
      equal to the default sub-profile, and the level indicated by each
      PLId field MUST be different than the default level.  All sequence
      parameter sets contained in each PSL MUST have the three bytes
      from profile_idc to level_idc, inclusive, equal to the preceding
      PLId.

         Informative note: This parameter allows for efficient level
         downgrade or upgrade in SDP Offer/Answer and out- of-band
         transport of parameter sets, simultaneously.

   use-level-src-parameter-sets:  This parameter MAY be used to indicate
      a receiver capability.  The value MAY be equal to either 0 or 1.
      When the parameter is not present, the value MUST be inferred to
      be equal to 0.  The value 0 indicates that the receiver does not
      understand the sprop-level-parameter-sets parameter, and does not
      understand the "fmtp" source attribute as specified in section 6.3
      of RFC 5576 [16], and will ignore sprop-level-parameter- sets when
      present, and will ignore sprop-parameter-sets when conveyed using
      the "fmtp" source attribute.  The value 1 indicates that the
      receiver understands the sprop-level- parameter-sets parameter,
      and understands the "fmtp" source attribute as specified in
      section 6.3 of RFC 5576 [16], and is capable of using parameter
      sets contained in the sprop-level- parameter-sets or contained in



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      the sprop-parameter-sets that is conveyed using the "fmtp" source
      attribute.

         Informative note: An RFC 3984 receiver does not understand
         sprop-level-parameter-sets, use-level-src- parameter-sets, or
         the "fmtp" source attribute as specified in section 6.3 of RFC
         5576 [16].  Therefore, during SDP Offer/Answer, an RFC 3984
         receiver as the answerer will simply ignore sprop-level-
         parameter-sets, when present in an offer, and sprop-parameter-
         sets conveyed using the "fmtp" source attribute as specified in
         section 6.3 of RFC 5576 [16].  Assume that the offered payload
         type was accepted at a level lower than the default level.  If
         the offered payload type included sprop-level-parameter-sets or
         included sprop-parameter-sets conveyed using the "fmtp" source
         attribute, and the offerer sees that the answerer has not
         included use-level-src-parameter-sets equal to 1 in the answer,
         the offerer knows that in-band transport of parameter sets is
         needed.

   in-band-parameter-sets:  This parameter MAY be used to indicate a
      receiver capability.  The value MAY be equal to either 0 or 1.
      The value 1 indicates that the receiver discards out-of-band
      parameter sets in sprop-parameter-sets and sprop-level-parameter-
      sets, therefore the sender MUST transmit all parameter sets in-
      band.  The value 0 indicates that the receiver utilizes out-of-
      band parameter sets included in sprop-parameter-sets and/or sprop-
      level-parameter-sets.  However, in this case, the sender MAY still
      choose to send parameter sets in-band.  When in-band- parameter-
      sets is equal to 1, use-level-src-parameter-sets MUST NOT be
      present or MUST be equal to 0.  When the parameter is not present,
      this receiver capability is not specified, and therefore the
      sender MAY send out-of-band parameter sets only, or it MAY send
      in-band-parameter-sets only, or it MAY send both.

   level-asymmetry-allowed:  This parameter MAY be used in SDP Offer/
      Answer to indicate whether level asymmetry, i.e., using a
      different level in the offerer-to-answerer direction than the
      level in the answerer- to-offerer direction, is allowed.  The
      value MAY be equal to either 0 or 1.  When the parameter is not
      present, the value MUST be inferred to be equal to 0.  The value 1
      in both the offer and the answer indicates that level asymmetry is
      allowed.  The value of 0 in either the offer or the answer
      indicates the level asymmetry is not allowed.








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      If "level-asymmetry-allowed" is equal to 0 (or not present) in
      either the offer or the answer, level asymmetry is not allowed.
      In this case, the level to use in the direction from the offerer
      to the answerer MUST be the same as the level to use in the
      opposite direction.

   packetization-mode:  This parameter signals the properties of an RTP
      payload type or the capabilities of a receiver implementation.
      Only a single configuration point can be indicated; thus, when
      capabilities to support more than one packetization-mode are
      declared, multiple configuration points (RTP payload types) must
      be used.

      When the value of packetization-mode is equal to 0 or
      packetization-mode is not present, the single NAL mode, as defined
      in section 6.2 of RFC 3984, MUST be used.  This mode is in use in
      standards using ITU-T Recommendation H.241 [5] (see section 12.1).
      When the value of packetization-mode is equal to 1, the non-
      interleaved mode, as defined in section 6.3 of RFC 3984, MUST be
      used.  When the value of packetization-mode is equal to 2, the
      interleaved mode, as defined in section 6.4 of RFC 3984, MUST be
      used.  The value of packetization-mode MUST be an integer in the
      range of 0 to 2, inclusive.

   sprop-interleaving-depth:  This parameter MUST NOT be present when
      packetization-mode is not present or the value of packetization-
      mode is equal to 0 or 1.  This parameter MUST be present when the
      value of packetization-mode is equal to 2.

      This parameter signals the properties of an RTP packet stream.  It
      specifies the maximum number of VCL NAL units that precede any VCL
      NAL unit in the RTP packet stream in transmission order and follow
      the VCL NAL unit in decoding order.  Consequently, it is
      guaranteed that receivers can reconstruct NAL unit decoding order
      when the buffer size for NAL unit decoding order recovery is at
      least the value of sprop- interleaving-depth + 1 in terms of VCL
      NAL units.

      The value of sprop-interleaving-depth MUST be an integer in the
      range of 0 to 32767, inclusive.

   sprop-deint-buf-req:  This parameter MUST NOT be present when
      packetization-mode is not present or the value of packetization-
      mode is equal to 0 or 1.  It MUST be present when the value of
      packetization- mode is equal to 2.






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      sprop-deint-buf-req signals the required size of the de-
      interleaving buffer for the RTP packet stream.  The value of the
      parameter MUST be greater than or equal to the maximum buffer
      occupancy (in units of bytes) required in such a de- interleaving
      buffer that is specified in section 7.2 of RFC 3984.  It is
      guaranteed that receivers can perform the de- interleaving of
      interleaved NAL units into NAL unit decoding order, when the de-
      interleaving buffer size is at least the value of sprop-deint-buf-
      req in terms of bytes.

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

         Informative note: sprop-deint-buf-req indicates the required
         size of the de-interleaving buffer only.  When network jitter
         can occur, an appropriately sized jitter buffer has to be
         provisioned for as well.

   deint-buf-cap:  This parameter signals the capabilities of a receiver
      implementation and indicates the amount of de-interleaving buffer
      space in units of bytes that the receiver has available for
      reconstructing the NAL unit decoding order.  A receiver is able to
      handle any stream for which the value of the sprop-deint-buf-req
      parameter is smaller than or equal to this parameter.

      If the parameter is not present, then a value of 0 MUST be used
      for deint-buf-cap.  The value of deint-buf-cap MUST be an integer
      in the range of 0 to 4294967295, inclusive.

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

   sprop-init-buf-time:  This parameter MAY be used to signal the
      properties of an RTP packet stream.  The parameter MUST NOT be
      present, if the value of packetization-mode is equal to 0 or 1.

      The parameter signals the initial buffering time that a receiver
      MUST wait before starting decoding to recover the NAL unit
      decoding order from the transmission order.  The parameter is the
      maximum value of (decoding time of the NAL unit - transmission
      time of a NAL unit), assuming reliable and instantaneous
      transmission, the same timeline for transmission and decoding, and
      that decoding starts when the first packet arrives.





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      An example of specifying the value of sprop-init-buf-time follows.
      A NAL unit stream is sent in the following interleaved order, in
      which the value corresponds to the decoding time and the
      transmission order is from left to right:

         0 2 1 3 5 4 6 8 7 ...

      Assuming a steady transmission rate of NAL units, the transmission
      times are:

         0 1 2 3 4 5 6 7 8 ...

      Subtracting the decoding time from the transmission time column-
      wise results in the following series:

         0 -1 1 0 -1 1 0 -1 1 ...

      Thus, in terms of intervals of NAL unit transmission times, the
      value of sprop-init-buf-time in this example is 1.  The parameter
      is coded as a non-negative base10 integer representation in clock
      ticks of a 90-kHz clock.  If the parameter is not present, then no
      initial buffering time value is defined.  Otherwise the value of
      sprop-init-buf-time MUST be an integer in the range of 0 to
      4294967295, inclusive.

      In addition to the signaled sprop-init-buf-time, receivers SHOULD
      take into account the transmission delay jitter buffering,
      including buffering for the delay jitter caused by mixers,
      translators, gateways, proxies, traffic-shapers, and other network
      elements.

   sprop-max-don-diff:  This parameter MAY be used to signal the
      properties of an RTP packet stream.  It MUST NOT be used to signal
      transmitter or receiver or codec capabilities.  The parameter MUST
      NOT be present if the value of packetization-mode is equal to 0 or
      1. sprop-max-don-diff is an integer in the range of 0 to 32767,
      inclusive.  If sprop-max-don-diff is not present, the value of the
      parameter is unspecified. sprop-max-don-diff is calculated as
      follows:

         sprop-max-don-diff = max{AbsDON(i) - AbsDON(j)}, for any i and
         any j>i,








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      where i and j indicate the index of the NAL unit in the
      transmission order and AbsDON denotes a decoding order number of
      the NAL unit that does not wrap around to 0 after 65535.  In other
      words, AbsDON is calculated as follows: Let m and n be consecutive
      NAL units in transmission order.  For the very first NAL unit in
      transmission order (whose index is 0), AbsDON(0) = DON(0).  For
      other NAL units, AbsDON is calculated as follows:

      If DON(m) == DON(n), AbsDON(n) = AbsDON(m)

      If (DON(m) < DON(n) and DON(n) - DON(m) < 32768),
      AbsDON(n) = AbsDON(m) + DON(n) - DON(m)

      If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768),
      AbsDON(n) = AbsDON(m) + 65536 - DON(m) + DON(n)

      If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768),
      AbsDON(n) = AbsDON(m) - (DON(m) + 65536 - DON(n))

      If (DON(m) > DON(n) and DON(m) - DON(n) < 32768),
      AbsDON(n) = AbsDON(m) - (DON(m) - DON(n))

      where DON(i) is the decoding order number of the NAL unit having
      index i in the transmission order.  The decoding order number is
      specified in section 5.5 of RFC 3984.

         Informative note: Receivers may use sprop-max-don-diff to
         trigger which NAL units in the receiver buffer can be passed to
         the decoder.

   max-rcmd-nalu-size:  This parameter MAY be used to signal the
      capabilities of a receiver.  The parameter MUST NOT be used for
      any other purposes.  The value of the parameter indicates the
      largest NALU size in bytes that the receiver can handle
      efficiently.  The parameter value is a recommendation, not a
      strict upper boundary.  The sender MAY create larger NALUs but
      must be aware that the handling of these may come at a higher cost
      than NALUs conforming to the limitation.

      The value of max-rcmd-nalu-size MUST be an integer in the range of
      0 to 4294967295, inclusive.  If this parameter is not specified,
      no known limitation to the NALU size exists.  Senders still have
      to consider the MTU size available between the sender and the
      receiver and SHOULD run MTU discovery for this purpose.







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      This parameter is motivated by, for example, an IP to H.223 video
      telephony gateway, where NALUs smaller than the H.223 transport
      data unit will be more efficient.  A gateway may terminate IP;
      thus, MTU discovery will normally not work beyond the gateway.

         Informative note: Setting this parameter to a lower than
         necessary value may have a negative impact.

   sar-understood:  This parameter MAY be used to indicate a receiver
      capability and not anything else.  The parameter indicates the
      maximum value of aspect_ratio_idc (specified in H.264 [4]) smaller
      than 255 that the receiver understands.  Table E-1 of H.264 [4]
      specifies aspect_ratio_idc equal to 0 as "unspecified", 1 to 16,
      inclusive, as specific Sample Aspect Ratios (SARs), 17 to 254,
      inclusive, as "reserved", and 255 as the Extended SAR, for which
      SAR width and SAR height are explicitly signaled.  Therefore, a
      receiver with a decoder according to H.264 [4] understands
      aspect_ratio_idc in the range of 1 to 16, inclusive and
      aspect_ratio_idc equal to 255, in the sense that the receiver
      knows what exactly the SAR is.  For such a receiver, the value of
      sar-understood is 16.  If in the future Table E-1 of H.264 [4] is
      extended, e.g., such that the SAR for aspect_ratio_idc equal to 17
      is specified, then for a receiver with a decoder that understands
      the extension, the value of sar-understood is 17.  For a receiver
      with a decoder according to the 2003 version of H.264 [4], the
      value of sar- understood is 13, as the minimum reserved
      aspect_ratio_idc therein is 14.

      When sar-understood is not present, the value MUST be inferred to
      be equal to 13.

   sar-supported:  This parameter MAY be used to indicate a receiver
      capability and not anything else.  The value of this parameter is
      an integer in the range of 1 to sar-understood, inclusive, equal
      to 255.  The value of sar-supported equal to N smaller than 255
      indicates that the reciever supports all the SARs corresponding to
      H.264 aspect_ratio_idc values (see Table E-1 of H.264 [4]) in the
      range from 1 to N, inclusive, without geometric distortion.  The
      value of sar-supported equal to 255 indicates that the receiver
      supports all sample aspect ratios which are expressible using two
      16-bit integer values as the numerator and denominator, i.e.,
      those that are expressible using the H.264 aspect_ratio_idc value
      of 255 (Extended_SAR, see Table E-1 of H.264 [4]), without
      geometric distortion.






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      H.264 compliant encoders SHOULD NOT send an aspect_ratio_idc equal
      to 0, or an aspect_ratio_idc larger than sar-understood and
      smaller than 255.  H.264 compliant encoders SHOULD send an
      aspect_ratio_idc that the receiver is able to display without
      geometrical distortion.  However, H.264 compliant encoders MAY
      choose to send pictures using any SAR.

      Note that the actual sample aspect ratio or extended sample aspect
      ratio, when present, of the stream is conveyed in the Video
      Usability Information (VUI) part of the sequence parameter set.

   Encoding considerations:  This type is only defined for transfer via
      RTP (RFC 3550) and is framed and binary, see section 4.8 in
      RFC4288.

   Security considerations:  See section X of RFC XXXX.

   Interoperability considerations:  None

   Published specification:  RFC XXXX and its reference section.

   Applications that use this media type:  None

   Additional information:  None

      Magic number(s):

      File extension(s):

      Macintosh file type code(s):

   Person & email address to contact for further information:
      Tom Kristensen <tom.kristensen@tandberg.com>, <tomkri@ifi.uio.no>

   Intended usage:  COMMON

   Restrictions on usage:  This type depends on RTP framing, and hence
      is only defined for transfer via RTP, ref RFC3550.  Transport
      within other framing protocols is not defined at this time.

   Author:  Tom Kristensen

   Change controller:  IETF Audio/Video Transport working group
      delegated from the IESG.






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7.  Mapping to SDP

   The mapping of the above defined payload format media subtype and its
   parameters SHALL be done according to Section 3 of RFC 4855 [8].

   An example of the fmtp attribute in the media representation of a
   level 2.2 bitstream is as follows:

      a=fmtp:97 profile-level-id=008016

7.1.  Offer/Answer Considerations

   When H264-RCDO is offered over RTP using SDP in an Offer/Answer model
   [2] for unicast and multicast usage, the limitations and rules
   described in Section 8.2.2 of RFC3984bis [3] apply.  Note that the
   profile_idc byte of the H264-RCDO profile-level-id parameter can only
   take the value of 0 (no profile).

   For interoperability with systems not supporting H264-RCDO, it is
   RECOMMENDED to offer the H264 media subtype as well.  As specified in
   RFC 3264 [2], listing the payload number for H264-RCDO before H264 in
   the format list on the "m=" line signals that H264-RCDO is preferred
   over H264.  An example where this scheme is applied:

      m=video 5555 RTP/AVP 97 98
      a=rtpmap:97 H264-RCDO/90000
      a=fmtp:97 profile-level-id=008016;max-mbps=42000;max-smbps=323500
      a=rtpmap:98 H264/90000
      a=fmtp:98 profile-level-id=428016;max-mbps=35000;max-smbps=323500

7.2.  Declarative SDP Considerations

   When H264-RCDO over RTP is offered with SDP in a declarative style,
   as in RTSP [14] or SAP [15], the considerations in Section 8.2.3 of
   RFC3984bis [3] apply.  Note that the profile_idc byte of the H264-
   RCDO profile-level-id parameter can only take the value of 0 (no
   profile).


8.  IANA Considerations

   This document requests that IANA registers H264-RCDO as specified in
   Section Section 6.1.  The media subtype is also requested to be added
   to the IANA registry for "RTP Payload Format MIME types"
   (http://www.iana.org/assignments/rtp-parameters).






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9.  Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [6], and in any applicable RTP profile.  The main
   security considerations for the RTP packet carrying the RTP payload
   format defined within this document are confidentiality, integrity
   and source authenticity.  Confidentiality is achieved by encryption
   of the RTP payload.  Integrity of the RTP packets through suitable
   cryptographic integrity protection mechanism.  Cryptographic system
   may also allow the authentication of the source of the payload.  A
   suitable security mechanism for this RTP payload format should
   provide confidentiality, integrity protection and at least source
   authentication capable of determining if an RTP packet is from a
   member of the RTP session or not.

   Note that the appropriate mechanism to provide security to RTP and
   payloads following this document may vary.  It is dependent on the
   application, the transport, and the signalling protocol employed.
   Therefore a single mechanism is not sufficient, although if suitable
   the usage of SRTP [11] is recommended.  Other mechanism that may be
   used are IPsec [12] and TLS [13] (RTP over TCP), but also other
   alternatives may exist.

   Refer also to section 9 of RFC3984bis [3], as no reasons for separate
   considerations are introduced in this document.


10.  Acknowledgements

   The authors would like to acknowledge Gisle Bjoentegaard and Arild
   Fuldseth for their technical contribution to the specification.  In
   the final phases Roni Even did a helpful review.


11.  References

11.1.  Normative References

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

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

   [3]   Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP Payload
         Format for H.264 Video", draft-ietf-avt-rtp-rfc3984bis-09 (work
         in progress), February 2010.



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   [4]   International Telecommunications Union, "Advanced video coding
         for generic audiovisual services", ITU-T Recommendation H.264,
         November 2007.

   [5]   International Telecommunications Union, "Extended video
         procedures and control signals for H.300-series terminals",
         ITU-T Recommendation H.241, May 2006.

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

   [7]   Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
         Conferences with Minimal Control", STD 65, RFC 3551, July 2003.

   [8]   Casner, S., "Media Type Registration of RTP Payload Formats",
         RFC 4855, February 2007.

   [9]   Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
         RFC 3548, July 2003.

11.2.  Informative references

   [10]  Freed, N. and J. Klensin, "Media Type Specifications and
         Registration Procedures", BCP 13, RFC 4288, December 2005.

   [11]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
         Norrman, "The Secure Real-time Transport Protocol (SRTP)",
         RFC 3711, March 2004.

   [12]  Kent, S. and K. Seo, "Security Architecture for the Internet
         Protocol", RFC 4301, December 2005.

   [13]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
         Protocol Version 1.2", RFC 5246, August 2008.

   [14]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
         Protocol (RTSP)", RFC 2326, April 1998.

   [15]  Handley, M., Perkins, C., and E. Whelan, "Session Announcement
         Protocol", RFC 2974, October 2000.

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






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Authors' Addresses

   Tom Kristensen
   TANDBERG
   Philip Pedersens vei 22
   N-1366 Lysaker
   Norway

   Phone: +47 67125125
   Email: tom.kristensen@tandberg.com, tomkri@ifi.uio.no
   URI:   http://www.tandberg.com


   Patrick Luthi
   TANDBERG
   Philip Pedersens vei 22
   N-1366 Lysaker
   Norway

   Email: patrick.luthi@tandberg.com
   URI:   http://www.tandberg.com






























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