RFC6185

Internet Engineering Task Force (IETF) T. Kristensen Request for Comments: 6185 P. Luthi Category: Standards Track TANDBERG ISSN: 2070-1721 May 2011

                     RTP Payload Format for
    H.264 Reduced-Complexity Decoding Operation (RCDO) Video

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 is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6185.

Copyright Notice

Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

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Introduction

ITU-T Recommendation H.241 [3] specifies a Reduced-Complexity Decoding Operation (RCDO) for use with H.264 [2] Baseline profile bitstreams. It also specifies a bitstream constraint associated with RCDO and a mechanism for signaling RCDO within the bitstream. The RCDO signaling 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 frame rates used in current implementations. This is achieved by reducing the processing requirements and thus reducing the decoding cost/resource consumption of the video processing.

This document defines media type parameters and allows use in systems based on the Session Description Protocol (SDP) [8] for signaling.

Conventions Used in This Document

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 [4].

Media Format Background

The Reduced-Complexity Decoding Operation (RCDO) for H.264 Baseline profile bitstreams is specified in Annex B of H.241 [3]. RCDO is specified as a separate H.264 mode and is distinct from any profile defined in H.264. An RCDO bitstream obeys all the constraints of the Baseline profile.

The media format is based on the H.264 RTP payload format as specified in RFC 6184 [1]. Therefore, RFC 6184 constitutes the basis for this document and is referred to several times.

In order to signal H.264 additional modes, Table 8-13 of H.241 [3] 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.

Payload Format

The payload format defined in Section 5 of RFC 6184 [1] SHALL be used. This includes the RTP header usage and the payload format in RFC 6184. Examples of typical RTP packets can be found in RFC 6184.

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.

Payload Format Parameters

This RTP payload format is identified using the H264-RCDO media subtype, which is registered in accordance with RFC 4855 [10], and using the template of RFC 4288 [13].

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 RFC 6184 [1].  Except for the profile-level-id
  parameter, for which new semantics are specified below, the
  optional parameters are copied from RFC 6184 [1] in order to
  provide a complete, self-contained media subtype registration to
  IANA.  The references are updated to match the numbering used in
  this document.

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

Type name: video

Subtype name: H264-RCDO

Required parameters:

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

  be 90000.

Optional parameters:

profile-level-id: A base16 RFC 4648 [9] (hexadecimal) representation

  of the following three bytes in the sequence parameter set NAL
  unit is specified in H.264 [2]: 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, constraint_set4_flag, constraint_set5_flag,
  and reserved_zero_2bits in bit-significance order, starting from
  the most-significant bit, and 3) level_idc.  Note that
  reserved_zero_2bits is required to be equal to 0 in H.264 [2], 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
  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
  minimum subset of coding tools a decoder has to support is the
  default sub-profile, and 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, it indicates the subset of coding tools, which
  is equal to the default sub-profile, that the codec supports for
  both receiving and sending.  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 (i.e., equivalent to
  profile-level-id 00800a) MUST be implied.

     Informative note: The definitions of the remaining optional
     parameters below are copied verbatim from Section 8.1 of RFC
     6184 [1].  Only the references are updated to match the
     numbering used in this document.

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
  sequence parameter set NAL unit specified in H.264 [2]: 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 if 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 bitrate 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 bitrate is up to max-br (inclusive), the coded
  picture buffer size is derived as specified in the semantics of
  the max-br parameter below, and the 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
     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 highest level, with the exception
  that the MaxMBPS value in Table A-1 of H.264 [2] 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 [2] 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 signaled,
  the MaxMBPS value in Table A-1 of H.264 [2] should be replaced
  with the result of the following computation:

  o If the parameter max-mbps is signaled, set a variable
    MaxMacroblocksPerSecond to the value of max-mbps.  Otherwise,
    set MaxMacroblocksPerSecond equal to the value of MaxMBPS in
    Table A-1 of H.264 [2] for the signaled highest level conveyed
    in the value of the profile-level-id parameter or the
    max-recv-level parameter.

  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 [2] 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 or equal to the value of
  MaxMBPS given explicitly as the value of the max-mbps parameter or
  implicitly in Table A-1 of H.264 [2] for the signaled 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-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 [2] 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 [2] 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 and in units of 1200 bits for the NAL HRD parameters.
  Note that this parameter does not use units of cpbBrVclFactor and
  cpbBrNALFactor (see Table A-1 of H.264 [2]).  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 [2] for the
  signaled highest level is replaced with the value of max-cpb
  (after taking cpbBrVclFactor and cpbBrNALFactor into consideration
  when needed).  The value of max-cpb (after taking cpbBrVclFactor
  and cpbBrNALFactor into consideration when needed) MUST be greater
  than or equal to the value of MaxCPB given in Table A-1 of H.264
  [2] for the highest level.  Senders MAY use this knowledge to
  construct coded video streams with greater variation of bitrate
  than can be achieved with the MaxCPB value in Table A-1 of H.264
  [2].

     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 a video
     decoder can be integrated with de-interleaving and de-jitter
     buffers of the receiver.

max-dpb: The value of max-dpb is an integer indicating the maximum

  decoded picture buffer size in units of 8/3 macroblocks.  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 MaxDpbMbs value in Table A-1 of H.264 [2] for
  the signaled highest level is replaced with the value of max-dpb *
  3 / 8.  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(max-dpb * 3 / 8 / ( PicWidthInMbs * FrameHeightInMbs), 16)

  Wherein PicWidthInMbs and FrameHeightInMbs are defined in H.264
  [2].

  The value of max-dpb MUST be greater than or equal to the value of
  MaxDpbMbs * 3 / 8, wherein the value of MaxDpbMbs is given in
  Table A-1 of H.264 [2] 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.

     Informative note: In RFC 3984, which is obsoleted by RFC 6184,
     the unit of this parameter was 1024 bytes.  The unit has been
     changed to 8/3 macroblocks in this document.  The reason for
     this change was due to the changes from the 2003 version of the
     H.264 specification referenced by RFC 3984 to the 2010 version
     of the H.264 specification referenced by this document,
     particularly the changes to Table A-1 in the H.264
     specification due to addition of color formats and bit depths
     not supported earlier.  The changed semantics of this parameter
     keeps backward compatibility to RFC 3984 and supports all
     profiles defined in the 2010 version of the H.264
     specification.

max-br: The value of max-br is an integer indicating the maximum

  video bitrate in units of 1000 bits per second for the VCL HRD
  parameters and in units of 1200 bits per second for the NAL HRD
  parameters.  Note that this parameter does not use units of
  cpbBrVclFactor and cpbBrNALFactor (see Table A-1 of H.264 [2]).

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

  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 (after taking cpbBrVclFactor and
    cpbBrNALFactor into consideration when needed) replaces the
    MaxBR value in Table A-1 of H.264 [2] 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 [2]: (MaxCPB of the signaled level) * max-br / (MaxBR of
    the signaled highest level).

  For example, if a receiver signals capability for Main profile
  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 (after taking cpbBrVclFactor and
  cpbBrNALFactor into consideration when needed) MUST be greater
  than or equal to the value MaxBR given in Table A-1 of H.264 [2]
  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.  The
     assumption that the network is capable of handling such
     bitrates at any given time cannot be made from the value of
     this parameter.  In particular, no conclusion can be drawn that
     the signaled bitrate is possible under congestion control
     constraints.

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, a value of 0
  MUST be used for redundant-pic-cap.  When present, the value 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 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 4648 [9] representations
  of parameter set NAL units as specified in Sections 7.3.2.1 and
  7.3.2.2 of H.264 [2].  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 hundred bytes.

     Informative note: When several payload types are offered in the
     SDP Offer/Answer model, each with its own sprop-parameter-sets
     parameter, 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.

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 that are different than the default level.
  All parameter sets associated with one level are clustered and
  prefixed with a three-byte field that 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 4648 [9] representation of the initial parameter set NAL units
  for the level.  Each pair of PLId:PSLs 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, does not

  understand the "fmtp" source attribute as specified in Section 6.3
  of RFC 5576 [14], 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,
  understands the "fmtp" source attribute as specified in Section
  6.3 of RFC 5576 [14], and is capable of using parameter sets
  contained in the sprop-level-parameter-sets or contained in 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 [14].  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 [14].  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 if 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, 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., sending media
  encoded at 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 that level asymmetry is not allowed.

  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 MUST be
  used.  This mode is in use in standards using ITU-T Recommendation
  H.241 [3] (see Section 12.1).  When the value of packetization-
  mode is equal to 1, the non-interleaved mode MUST be used.  When
  the value of packetization-mode is equal to 2, the interleaved
  mode 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 that
  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.

  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 6184 [1].  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
  commencement of decoding when the first packet arrives.

  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, 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,

  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 6184 [1].

     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.

  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 nothing else.  The parameter indicates the maximum
  value of aspect_ratio_idc (specified in H.264 [2]) smaller than
  255 that the receiver understands.  Table E-1 of H.264 [2]
  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 [2] 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 exactly what the SAR is.  For such a receiver, the value of
  sar-understood is 16.  In the future, if Table E-1 of H.264 [2] 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 [2], 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 nothing 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 receiver supports all the SARs corresponding to
  H.264 aspect_ratio_idc values (see Table E-1 of H.264 [2]) 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 that 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 [2]), without
  geometric distortion.

  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 RFC
  4288).

Security considerations: See Section 9 of RFC 6185.

Interoperability considerations: None

Published specification: RFC 6185 and its reference section

Applications that use this media type: Video streaming and

  conferencing applications

Additional information: None

  Magic number(s):

  File extension(s):

  Macintosh file type code(s):

Person & email address to contact for further information:

  Tom Kristensen <[email protected]>, <[email protected]>

Intended usage: COMMON

Restrictions on usage: This type depends on RTP framing; hence, it

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

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 [10].

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

Offer/Answer Considerations

When H264-RCDO is offered over RTP using SDP in an Offer/Answer model [5] for unicast and multicast usage, the limitations and rules described in Section 8.2.2 of RFC 6184 [1] 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 [5], 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. Following is 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

Declarative SDP Considerations

When H264-RCDO over RTP is offered with SDP in a declarative style, as in the Real Time Streaming Protocol (RTSP) [11] or the Session Announcement Protocol (SAP) [12], the considerations in Section 8.2.3 of RFC 6184 [1] apply. Note that the profile_idc byte of the H264- RCDO profile-level-id parameter can only take the value of 0 (no profile).

IANA Considerations

IANA has registered H264-RCDO as specified in Section 6.1. The media subtype has also been added to the IANA registry for "RTP Payload Format MIME types" (http://www.iana.org).

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. Refer also to the security considerations of the RTP Payload Format for H.264 Video specification in RFC 6184 [1]. No additional security considerations are introduced by this specification.

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] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP Payload

     Format for H.264 Video", RFC 6184, May 2011.

[2] International Telecommunications Union, "Advanced video coding

     for generic audiovisual services", ITU-T Recommendation H.264,
     March 2010.

[3] International Telecommunications Union, "Extended video

     procedures and control signals for H.300-series terminals",
     ITU-T Recommendation H.241, May 2006.

[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement

     Levels", BCP 14, RFC 2119, March 1997.

[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with

     Session Description Protocol (SDP)", RFC 3264, June 2002.

[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] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session

     Description Protocol", RFC 4566, July 2006.

[9] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",

     RFC 4648, October 2006.

[10] Casner, S., "Media Type Registration of RTP Payload Formats",

     RFC 4855, February 2007.

11.2. Informative References

[11] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming

     Protocol (RTSP)", RFC 2326, April 1998.

[12] Handley, M., Perkins, C., and E. Whelan, "Session Announcement

     Protocol", RFC 2974, October 2000.

[13] Freed, N. and J. Klensin, "Media Type Specifications and

     Registration Procedures", BCP 13, RFC 4288, December 2005.

[14] Lennox, J., Ott, J., and T. Schierl, "Source-Specific Media

     Attributes in the Session Description Protocol (SDP)",
     RFC 5576, June 2009.

Authors' Addresses

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

Phone: +47 67125125 EMail: [email protected], [email protected] URI: http://www.tandberg.com

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

EMail: [email protected] URI: http://www.tandberg.com