RTP Payload Format for Versatile Video Coding (VVC)
draft-ietf-avtcore-rtp-vvc-12

Document Type Active Internet-Draft (avtcore WG)
Authors Shuai Zhao  , Stephan Wenger  , Yago Sanchez  , Ye-Kui Wang 
Last updated 2021-10-25
Replaces draft-zhao-avtcore-rtp-vvc
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avtcore                                                          S. Zhao
Internet-Draft                                                 S. Wenger
Intended status: Standards Track                                 Tencent
Expires: 28 April 2022                                        Y. Sanchez
                                                          Fraunhofer HHI
                                                              Y.-K. Wang
                                                          Bytedance Inc.
                                                         25 October 2021

          RTP Payload Format for Versatile Video Coding (VVC)
                     draft-ietf-avtcore-rtp-vvc-12

Abstract

   This memo describes an RTP payload format for the video coding
   standard ITU-T Recommendation H.266 and ISO/IEC International
   Standard 23090-3, both also known as Versatile Video Coding (VVC) and
   developed by the Joint Video Experts Team (JVET).  The RTP payload
   format allows for packetization of one or more Network Abstraction
   Layer (NAL) units in each RTP packet payload as well as fragmentation
   of a NAL unit into multiple RTP packets.  The payload format has wide
   applicability in videoconferencing, Internet video streaming, and
   high-bitrate entertainment-quality video, among other applications.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 28 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview of the VVC Codec . . . . . . . . . . . . . . . .   3
       1.1.1.  Coding-Tool Features (informative)  . . . . . . . . .   3
       1.1.2.  Systems and Transport Interfaces (informative)  . . .   6
       1.1.3.  High-Level Picture Partitioning (informative) . . . .  11
       1.1.4.  NAL Unit Header . . . . . . . . . . . . . . . . . . .  13
     1.2.  Overview of the Payload Format  . . . . . . . . . . . . .  15
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .  15
   3.  Definitions and Abbreviations . . . . . . . . . . . . . . . .  15
     3.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .  15
       3.1.1.  Definitions from the VVC Specification  . . . . . . .  15
       3.1.2.  Definitions Specific to This Memo . . . . . . . . . .  18
     3.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .  19
   4.  RTP Payload Format  . . . . . . . . . . . . . . . . . . . . .  20
     4.1.  RTP Header Usage  . . . . . . . . . . . . . . . . . . . .  20
     4.2.  Payload Header Usage  . . . . . . . . . . . . . . . . . .  22
     4.3.  Payload Structures  . . . . . . . . . . . . . . . . . . .  22
       4.3.1.  Single NAL Unit Packets . . . . . . . . . . . . . . .  23
       4.3.2.  Aggregation Packets (APs) . . . . . . . . . . . . . .  23
       4.3.3.  Fragmentation Units . . . . . . . . . . . . . . . . .  27
     4.4.  Decoding Order Number . . . . . . . . . . . . . . . . . .  30
   5.  Packetization Rules . . . . . . . . . . . . . . . . . . . . .  31
   6.  De-packetization Process  . . . . . . . . . . . . . . . . . .  32
   7.  Payload Format Parameters . . . . . . . . . . . . . . . . . .  34
     7.1.  Media Type Registration . . . . . . . . . . . . . . . . .  34
     7.2.  SDP Parameters  . . . . . . . . . . . . . . . . . . . . .  46
       7.2.1.  Mapping of Payload Type Parameters to SDP . . . . . .  46
       7.2.2.  Usage with SDP Offer/Answer Model . . . . . . . . . .  47
       7.2.3.  Usage in Declarative Session Descriptions . . . . . .  56
       7.2.4.  Considerations for Parameter Sets . . . . . . . . . .  57
   8.  Use with Feedback Messages  . . . . . . . . . . . . . . . . .  57
     8.1.  Picture Loss Indication (PLI) . . . . . . . . . . . . . .  58
     8.2.  Full Intra Request (FIR)  . . . . . . . . . . . . . . . .  58
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  58
   10. Congestion Control  . . . . . . . . . . . . . . . . . . . . .  60
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  61
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  61

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   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  61
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  61
     13.2.  Informative References . . . . . . . . . . . . . . . . .  63
   Appendix A.  Change History . . . . . . . . . . . . . . . . . . .  64
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  64

1.  Introduction

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

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

1.1.  Overview of the VVC Codec

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

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

1.1.1.  Coding-Tool Features (informative)

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

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

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

   Coding blocks and transform structure

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

   Entropy coding

   Similar to HEVC, VVC uses a single entropy-coding engine, which is
   based on context adaptive binary arithmetic coding [CABAC], but with
   the support of multi-window sizes.  The window sizes can be
   initialized differently for different context models.  Due to such a
   design, it has more efficient adaptation speed and better coding
   efficiency.  A joint chroma residual coding scheme is applied to
   further exploit the correlation between the residuals of two color
   components.  In VVC, different residual coding schemes are applied
   for regular transform coefficients and residual samples generated
   using transform-skip mode.

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   In-loop filtering

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

   Motion prediction and coding

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

   Intra prediction and intra-coding

   To capture the diversified local image texture directions with finer
   granularity, VVC supports 65 angular directions instead of 33
   directions in HEVC.  The intra mode coding is based on a 6-most-
   probable-mode scheme, and the 6 most probable modes are derived using
   the neighboring intra prediction directions.  In addition, to deal
   with the different distributions of intra prediction angles for
   different block aspect ratios, a wide-angle intra prediction (WAIP)

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   scheme is applied in VVC by including intra prediction angles beyond
   those present in HEVC.  Unlike HEVC which only allows using the most
   adjacent line of reference samples for intra prediction, VVC also
   allows using two further reference lines, as known as multi-
   reference-line (MRL) intra prediction.  The additional reference
   lines can be only used for the 6 most probable intra prediction
   modes.  To capture the strong correlation between different colour
   components, in VVC, a cross-component linear mode (CCLM) is utilized
   which assumes a linear relationship between the luma sample values
   and their associated chroma samples.  For intra prediction, VVC also
   applies a position-dependent prediction combination (PDPC) for
   refining the prediction samples closer to the intra prediction block
   boundary.  Matrix-based intra prediction (MIP) modes are also used in
   VVC which generates an up to 8x8 intra prediction block using a
   weighted sum of downsampled neighboring reference samples, and the
   weights are hardcoded constants.

   Other coding-tool feature

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

1.1.2.  Systems and Transport Interfaces (informative)

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

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

   Decoding capability information

   The decoding capability information includes parameters that stay
   constant for the lifetime of a Video Bitstream, which in IETF terms
   can translate to the lifetime of a session.  Such information
   includes profile, level, and sub-profile information to determine a
   maximum capability interop point that is guaranteed to be never
   exceeded, even if splicing of video sequences occurs within a
   session.  It further includes constraint fields (most of which are

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   flags), which can optionally be set to indicate that the video
   bitstream will be constraint in the use of certain features as
   indicated by the values of those fields.  With this, a bitstream can
   be labelled as not using certain tools, which allows among other
   things for resource allocation in a decoder implementation.

   Video parameter set

   The video parameter set (VPS) pertains to one or more coded video
   sequences (CVSs) of multiple layers covering the same range of access
   units, and includes, among other information, decoding dependency
   expressed as information for reference picture list construction of
   enhancement layers.  The VPS provides a "big picture" of a scalable
   sequence, including what types of operation points are provided, the
   profile, tier, and level of the operation points, and some other
   high-level properties of the bitstream that can be used as the basis
   for session negotiation and content selection, etc.  One VPS may be
   referenced by one or more sequence parameter sets.

   Sequence parameter set

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

   Picture and adaptation parameter set

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

   Picture header

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

   Profile, tier, and level

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

   Sub-profiles

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

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   as well as walled-garden video services will take advantage of this
   labelling system.  In contrast to "normal" profiles, it is expected
   that sub-profiles may indicate encoder choices traditionally left
   open in the (decoder- centric) video coding specs, such as GOP
   structures, minimum/maximum QP values, and the mandatory use of
   certain tools or SEI messages.

   General constraint fields

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

   Temporal scalability support

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

   Reference picture resampling (RPR)

   In AVC and HEVC, the spatial resolution of pictures cannot change
   unless a new sequence using a new SPS starts, with an IRAP picture.
   VVC enables picture resolution change within a sequence at a position
   without encoding an IRAP picture, which is always intra-coded.  This
   feature is sometimes referred to as reference picture resampling
   (RPR), as the feature needs resampling of a reference picture used
   for inter prediction when that reference picture has a different
   resolution than the current picture being decoded.  RPR allows
   resolution change without the need of coding an IRAP picture, which
   causes a momentary bit rate spike in streaming or video conferencing
   scenarios, e.g., to cope with network condition changes.  RPR can
   also be used in application scenarios wherein zooming of the entire
   video region or some region of interest is needed.

   Spatial, SNR, and multiview scalability

   VVC includes support for spatial, SNR, and multiview scalability.
   Scalable video coding is widely considered to have technical benefits
   and enrich services for various video applications.  Until recently,

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   however, the functionality has not been included in the first version
   of specifications of the video codecs.  In VVC, however, all those
   forms of scalability are supported in the first version of VVC
   natively through the signaling of the layer_id in the NAL unit
   header, the VPS which associates layers with given layer_ids to each
   other, reference picture selection, reference picture resampling for
   spatial scalability, and a number of other mechanisms not relevant
   for this memo.

      Spatial scalability

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

      SNR scalability

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

      Multiview scalability

         The first version of VVC also supports multiview scalability,
         wherein a multi-layer bitstream carries layers representing
         multiple views, and one or more of the represented views can be
         output at the same time.

   SEI messages

   Supplementary enhancement information (SEI) messages are information
   in the bitstream that do not influence the decoding process as
   specified in the VVC spec, but address issues of representation/
   rendering of the decoded bitstream, label the bitstream for certain
   applications, among other, similar tasks.  The overall concept of SEI
   messages and many of the messages themselves has been inherited from

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   the H.264 and HEVC specs.  Except for the SEI messages that affect
   the specification of the hypothetical reference decoder (HRD), other
   SEI messages for use in the VVC environment, which are generally
   useful also in other video coding technologies, are not included in
   the main VVC specification but in a companion specification [VSEI].

1.1.3.  High-Level Picture Partitioning (informative)

   VVC inherited the concept of tiles and wavefront parallel processing
   (WPP) from HEVC, with some minor to moderate differences.  The basic
   concept of slices was kept in VVC but designed in an essentially
   different form.  VVC is the first video coding standard that includes
   subpictures as a feature, which provides the same functionality as
   HEVC motion-constrained tile sets (MCTSs) but designed differently to
   have better coding efficiency and to be friendlier for usage in
   application systems.  More details of these differences are described
   below.

   Tiles and WPP

   Same as in HEVC, a picture can be split into tile rows and tile
   columns in VVC, in-picture prediction across tile boundaries is
   disallowed, etc.  However, the syntax for signaling of tile
   partitioning has been simplified, by using a unified syntax design
   for both the uniform and the non-uniform mode.  In addition,
   signaling of entry point offsets for tiles in the slice header is
   optional in VVC while it is mandatory in HEVC.  The WPP design in VVC
   has two differences compared to HEVC: i) The CTU row delay is reduced
   from two CTUs to one CTU; ii) Signaling of entry point offsets for
   WPP in the slice header is optional in VVC while it is mandatory in
   HEVC.

   Slices

   In VVC, the conventional slices based on CTUs (as in HEVC) or
   macroblocks (as in AVC) have been removed.  The main reasoning behind
   this architectural change is as follows.  The advances in video
   coding since 2003 (the publication year of AVC v1) have been such
   that slice-based error concealment has become practically impossible,
   due to the ever-increasing number and efficiency of in-picture and
   inter-picture prediction mechanisms.  An error-concealed picture is
   the decoding result of a transmitted coded picture for which there is
   some data loss (e.g., loss of some slices) of the coded picture or a
   reference picture for at least some part of the coded picture is not
   error-free (e.g., that reference picture was an error-concealed
   picture).  For example, when one of the multiple slices of a picture
   is lost, it may be error-concealed using an interpolation of the
   neighboring slices.  While advanced video coding prediction

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   mechanisms provide significantly higher coding efficiency, they also
   make it harder for machines to estimate the quality of an error-
   concealed picture, which was already a hard problem with the use of
   simpler prediction mechanisms.  Advanced in-picture prediction
   mechanisms also cause the coding efficiency loss due to splitting a
   picture into multiple slices to be more significant.  Furthermore,
   network conditions become significantly better while at the same time
   techniques for dealing with packet losses have become significantly
   improved.  As a result, very few implementations have recently used
   slices for maximum transmission unit size matching.  Instead,
   substantially all applications where low-delay error resilience is
   required (e.g., video telephony and video conferencing) rely on
   system/transport-level error resilience (e.g., retransmission,
   forward error correction) and/or picture-based error resilience tools
   (feedback-based error resilience, insertion of IRAPs, scalability
   with higher protection level of the base layer, and so on).
   Considering all the above, nowadays it is very rare that a picture
   that cannot be correctly decoded is passed to the decoder, and when
   such a rare case occurs, the system can afford to wait for an error-
   free picture to be decoded and available for display without
   resulting in frequent and long periods of picture freezing seen by
   end users.

   Slices in VVC have two modes: rectangular slices and raster-scan
   slices.  The rectangular slice, as indicated by its name, covers a
   rectangular region of the picture.  Typically, a rectangular slice
   consists of several complete tiles.  However, it is also possible
   that a rectangular slice is a subset of a tile and consists of one or
   more consecutive, complete CTU rows within a tile.  A raster-scan
   slice consists of one or more complete tiles in a tile raster scan
   order, hence the region covered by a raster-scan slices need not but
   could have a non-rectangular shape, but it may also happen to have
   the shape of a rectangle.  The concept of slices in VVC is therefore
   strongly linked to or based on tiles instead of CTUs (as in HEVC) or
   macroblocks (as in AVC).

   Subpictures

   VVC is the first video coding standard that includes the support of
   subpictures as a feature.  Each subpicture consists of one or more
   complete rectangular slices that collectively cover a rectangular
   region of the picture.  A subpicture may be either specified to be
   extractable (i.e., coded independently of other subpictures of the
   same picture and of earlier pictures in decoding order) or not
   extractable.  Regardless of whether a subpicture is extractable or
   not, the encoder can control whether in-loop filtering (including
   deblocking, SAO, and ALF) is applied across the subpicture boundaries
   individually for each subpicture.

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   Functionally, subpictures are similar to the motion-constrained tile
   sets (MCTSs) in HEVC.  They both allow independent coding and
   extraction of a rectangular subset of a sequence of coded pictures,
   for use cases like viewport-dependent 360o video streaming
   optimization and region of interest (ROI) applications.

   There are several important design differences between subpictures
   and MCTSs.  First, the subpictures feature in VVC allows motion
   vectors of a coding block pointing outside of the subpicture even
   when the subpicture is extractable by applying sample padding at
   subpicture boundaries in this case, similarly as at picture
   boundaries.  Second, additional changes were introduced for the
   selection and derivation of motion vectors in the merge mode and in
   the decoder side motion vector refinement process of VVC.  This
   allows higher coding efficiency compared to the non-normative motion
   constraints applied at the encoder-side for MCTSs.  Third, rewriting
   of SHs (and PH NAL units, when present) is not needed when extracting
   one or more extractable subpictures from a sequence of pictures to
   create a sub-bitstream that is a conforming bitstream.  In sub-
   bitstream extractions based on HEVC MCTSs, rewriting of SHs is
   needed.  Note that in both HEVC MCTSs extraction and VVC subpictures
   extraction, rewriting of SPSs and PPSs is needed.  However, typically
   there are only a few parameter sets in a bitstream, while each
   picture has at least one slice, therefore rewriting of SHs can be a
   significant burden for application systems.  Fourth, slices of
   different subpictures within a picture are allowed to have different
   NAL unit types.  Fifth, VVC specifies HRD and level definitions for
   subpicture sequences, thus the conformance of the sub-bitstream of
   each extractable subpicture sequence can be ensured by encoders.

1.1.4.  NAL Unit Header

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

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

                   The Structure of the VVC NAL Unit Header.

                                  Figure 1

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

   F: 1 bit

      forbidden_zero_bit.  Required to be zero in VVC.  Note that the
      inclusion of this bit in the NAL unit header was to enable
      transport of VVC video over MPEG-2 transport systems (avoidance of
      start code emulations) [MPEG2S].  In the context of this memo the
      value 1 may be used to indicate a syntax violation, e.g., for a
      NAL unit resulted from aggregating a number of fragmented units of
      a NAL unit but missing the last fragment, as described in the last
      sentence of section 4.3.3.

   Z: 1 bit

      nuh_reserved_zero_bit.  Required to be zero in VVC, and reserved
      for future extensions by ITU-T and ISO/IEC.

      This memo does not overload the "Z" bit for local extensions, as
      a) overloading the "F" bit is sufficient and b) to preserve the
      usefulness of this memo to possible future versions of [VVC].

   LayerId: 6 bits

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

   Type: 5 bits

      nal_unit_type.  This field specifies the NAL unit type as defined
      in Table 5 of [VVC].  For a reference of all currently defined NAL
      unit types and their semantics, please refer to Section 7.4.2.2 in
      [VVC].

   TID: 3 bits

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

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1.2.  Overview of the Payload Format

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

   *  Usage of RTP header with this payload format

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

   *  Transmission of VVC NAL units of the same bitstream within a
      single RTP stream

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

   *  Usage of RTCP feedback messages

2.  Conventions

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

3.  Definitions and Abbreviations

3.1.  Definitions

   This document uses the terms and definitions of VVC.  Section 3.1.1
   lists relevant definitions from [VVC] for convenience.  Section 3.1.2
   provides definitions specific to this memo.  All the used terms and
   definitions in this memo are verbatim copies of [VVC] specification.

3.1.1.  Definitions from the VVC Specification

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

   Slice header (SH): A part of a coded slice containing the data
   elements pertaining to all tiles or CTU rows within a tile
   represented in the slice.

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

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

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

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

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

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

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

3.1.2.  Definitions Specific to This Memo

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

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

   NAL unit decoding order: A NAL unit order that conforms to the
   constraints on NAL unit order given in Section 7.4.2.4 in [VVC],
   follow the Order of NAL units in the bitstream.

   RTP stream (See [RFC7656]): Within the scope of this memo, one RTP
   stream is utilized to transport a VVC bitstream, which may contain
   one or more layers, and each layer may contain one or more temporal
   sublayers.

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

3.2.  Abbreviations

   AU         Access Unit

   AP         Aggregation Packet

   APS        Adaptation Parameter Set

   CTU        Coding Tree Unit

   CVS        Coded Video Sequence

   DPB        Decoded Picture Buffer

   DCI        Decoding Capability Information

   DON        Decoding Order Number

   FIR        Full Intra Request

   FU         Fragmentation Unit

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   GDR        Gradual Decoding Refresh

   HRD        Hypothetical Reference Decoder

   IDR        Instantaneous Decoding Refresh

   MANE       Media-Aware Network Element

   MTU        Maximum Transfer Unit

   NAL        Network Abstraction Layer

   NALU       Network Abstraction Layer Unit

   PLI        Picture Loss Indication

   PPS        Picture Parameter Set

   RPS        Reference Picture Set

   RPSI       Reference Picture Selection Indication

   SEI        Supplemental Enhancement Information

   SLI        Slice Loss Indication

   SPS        Sequence Parameter Set

   VCL        Video Coding Layer

   VPS        Video Parameter Set

4.  RTP Payload Format

4.1.  RTP Header Usage

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

   The RTP payload (and the settings for some RTP header bits) for
   aggregation packets and fragmentation units are specified in
   Section 4.3.2 and Section 4.3.3, respectively.

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

                        RTP Header According to {{RFC3550}}

                                  Figure 2

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

   Marker bit (M): 1 bit

      Set for the last packet, in transmission order, among each set of
      packets that contain NAL units of one access unit.  This is in
      line with the normal use of the M bit in video formats to allow an
      efficient playout buffer handling.

   Payload Type (PT): 7 bits

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

   Sequence Number (SN): 16 bits

      Set and used in accordance with [RFC3550].

   Timestamp: 32 bits

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      The RTP timestamp is set to the sampling timestamp of the content.
      A 90 kHz clock rate MUST be used.  If the NAL unit has no timing
      properties of its own (e.g., parameter set and SEI NAL units), the
      RTP timestamp MUST be set to the RTP timestamp of the coded
      pictures of the access unit in which the NAL unit (according to
      Section 7.4.2.4 of [VVC]) is included.  Receivers MUST use the RTP
      timestamp for the display process, even when the bitstream
      contains picture timing SEI messages or decoding unit information
      SEI messages as specified in [VVC].

         Informative note: When picture timing SEI messages are present,
         the RTP sender is responsible to ensure that the RTP timestamps
         are consistent with the timing information carried in the
         picture timing SEI messages.

   Synchronization source (SSRC): 32 bits

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

4.2.  Payload Header Usage

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

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

4.3.  Payload Structures

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

   The three different payload structures are as follows:

   *  Single NAL unit packet: Contains a single NAL unit in the payload,
      and the NAL unit header of the NAL unit also serves as the payload
      header.  This payload structure is specified in Section 4.4.1.

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

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

4.3.1.  Single NAL Unit Packets

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

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

                  The Structure of a Single NAL Unit Packet

                                  Figure 3

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

4.3.2.  Aggregation Packets (APs)

   Aggregation Packets (APs) can reduce packetization overhead for small
   NAL units, such as most of the non-VCL NAL units, which are often
   only a few octets in size.

   An AP aggregates NAL units of one access unit and it can only contain
   NAL units from one AU.  Each NAL unit to be carried in an AP is
   encapsulated in an aggregation unit.  NAL units aggregated in one AP
   are included in NAL unit decoding order.

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

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    PayloadHdr (Type=28)       |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                                                               |
    |             two or more aggregation units                     |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   The Structure of an Aggregation Packet

                                  Figure 4

   The fields in the payload header of an AP are set as follows.  The F
   bit MUST be equal to 0 if the F bit of each aggregated NAL unit is
   equal to zero; otherwise, it MUST be equal to 1.  The Type field MUST
   be equal to 28.

   The value of LayerId MUST be equal to the lowest value of LayerId of
   all the aggregated NAL units.  The value of TID MUST be the lowest
   value of TID of all the aggregated NAL units.

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

      Informative Note: If a system envisions sub-picture level or
      picture level modifications, for example by removing sub-pictures
      or pictures of a particular layer, a good design choice on the
      sender's side would be to aggregate NAL units belonging to only
      the same sub-picture or picture of a particular layer.

   An AP MUST carry at least two aggregation units and can carry as many
   aggregation units as necessary; however, the total amount of data in
   an AP obviously MUST fit into an IP packet, and the size SHOULD be
   chosen so that the resulting IP packet is smaller than the MTU size
   so to avoid IP layer fragmentation.  An AP MUST NOT contain FUs
   specified in Section 4.3.3.  APs MUST NOT be nested; i.e., an AP can
   not contain another AP.

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

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

           The Structure of the First Aggregation Unit in an AP

                                  Figure 5

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

   If sprop-max-don-diff is greater than 0, the DONL field MUST be
   present in an aggregation unit that is the first aggregation unit in
   an AP, and the variable DON for the aggregated NAL unit is derived as
   equal to the value of the DONL field, and the variable DON for an
   aggregation unit that is not the first aggregation unit in an AP
   aggregated NAL unit is derived as equal to the DON of the preceding
   aggregated NAL unit in the same AP plus 1 modulo 65536.  Otherwise
   (sprop-max-don-diff is equal to 0), the DONL field MUST NOT be
   present in an aggregation unit that is the first aggregation unit in
   an AP.

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

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

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

                                  Figure 6

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

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          RTP Header                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   PayloadHdr (Type=28)        |         NALU 1 Size           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          NALU 1 HDR           |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+         NALU 1 Data           |
    |                   . . .                                       |
    |                                                               |
    +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  . . .        | NALU 2 Size                   | NALU 2 HDR    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | NALU 2 HDR    |                                               |
    +-+-+-+-+-+-+-+-+              NALU 2 Data                      |
    |                   . . .                                       |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

                                  Figure 7

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

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     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          RTP Header                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   PayloadHdr (Type=28)        |        NALU 1 DONL            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          NALU 1 Size          |            NALU 1 HDR         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                 NALU 1 Data   . . .                           |
    |                                                               |
    +        . . .                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :          NALU 2 Size          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          NALU 2 HDR           |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+          NALU 2 Data          |
    |                                                               |
    |        . . .                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

                                  Figure 8

4.3.3.  Fragmentation Units

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

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

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

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

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     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   PayloadHdr (Type=29)        |   FU header   | DONL (cond)   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |   DONL (cond) |                                               |
    |-+-+-+-+-+-+-+-+                                               |
    |                         FU payload                            |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          The Structure of an FU

                                  Figure 9

   The fields in the payload header are set as follows.  The Type field
   MUST be equal to 29.  The fields F, LayerId, and TID MUST be equal to
   the fields F, LayerId, and TID, respectively, of the fragmented NAL
   unit.

   The FU header consists of an S bit, an E bit, an R bit and a 5-bit
   FuType field, as shown in Figure 10.

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

                       The Structure of FU Header

                                 Figure 10

   The semantics of the FU header fields are as follows:

   S: 1 bit

      When set to 1, the S bit indicates the start of a fragmented NAL
      unit, i.e., the first byte of the FU payload is also the first
      byte of the payload of the fragmented NAL unit.  When the FU
      payload is not the start of the fragmented NAL unit payload, the S
      bit MUST be set to 0.

   E: 1 bit

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      When set to 1, the E bit indicates the end of a fragmented NAL
      unit, i.e., the last byte of the payload is also the last byte of
      the fragmented NAL unit.  When the FU payload is not the last
      fragment of a fragmented NAL unit, the E bit MUST be set to 0.

   P: 1 bit

      When set to 1, the P bit indicates the last FU of the last VCL NAL
      unit of a coded picture, i.e., the last byte of the FU payload is
      also the last byte of the last VCL NAL unit of the coded picture.
      When the FU payload is not the last fragment of the last VCL NAL
      unit of a coded picture, the P bit MUST be set to 0.

   FuType: 5 bits

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

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

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

   A non-fragmented NAL unit MUST NOT be transmitted in one FU; i.e.,
   the Start bit and End bit must not both be set to 1 in the same FU
   header.

   The FU payload consists of fragments of the payload of the fragmented
   NAL unit so that if the FU payloads of consecutive FUs, starting with
   an FU with the S bit equal to 1 and ending with an FU with the E bit
   equal to 1, are sequentially concatenated, the payload of the
   fragmented NAL unit can be reconstructed.  The NAL unit header of the
   fragmented NAL unit is not included as such in the FU payload, but
   rather the information of the NAL unit header of the fragmented NAL
   unit is conveyed in F, LayerId, and TID fields of the FU payload
   headers of the FUs and the FuType field of the FU header of the FUs.
   An FU payload MUST NOT be empty.

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

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

4.4.  Decoding Order Number

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

         Informative note: When two consecutive NAL units in the NAL
         unit decoding order have different values of AbsDon, the
         absolute difference between the two AbsDon values may be
         greater than or equal to 1.

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

5.  Packetization Rules

   The following packetization rules apply:

   *  If sprop-max-don-diff is greater than 0, the transmission order of
      NAL units carried in the RTP stream MAY be different than the NAL
      unit decoding order.  Otherwise (sprop-max-don-diff is equal to
      0), the transmission order of NAL units carried in the RTP stream
      MUST be the same as the NAL unit decoding order.

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

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

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

6.  De-packetization Process

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

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

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

   NAL units with NAL unit type values in the range of 0 to 27,
   inclusive, may be passed to the decoder.  NAL-unit-like structures
   with NAL unit type values in the range of 28 to 31, inclusive, MUST
   NOT be passed to the decoder.

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

   The de-packetization process extracts the NAL units from the RTP
   packets in an RTP stream as follows.  When an RTP packet carries a
   single NAL unit packet, the payload of the RTP packet is extracted as
   a single NAL unit, excluding the DONL field, i.e., third and fourth
   bytes, when sprop-max-don-diff is greater than 0.  When an RTP packet
   carries an Aggregation Packet, several NAL units are extracted from
   the payload of the RTP packet.  In this case, each NAL unit
   corresponds to the part of the payload of each aggregation unit that
   follows the NALU size field as described in Section 4.3.2.  When an
   RTP packet carries a Fragmentation Unit (FU), all RTP packets from
   the first FU (with the S field equal to 1) of the fragmented NAL unit
   up to the last FU (with the E field equal to 1) of the fragmented NAL
   unit are collected.  The NAL unit is extracted from these RTP packets
   by concatenating all FU payloads in the same order as the
   corresponding RTP packets and appending the NAL unit header with the
   fields F, LayerId, and TID, set to equal to the values of the fields
   F, LayerId, and TID in the payload header of the FUs respectively,
   and with the NAL unit type set equal to the value of the field FuType
   in the FU header of the FUs, as described in Section 4.3.3.

   When sprop-max-don-diff is equal to 0, the de-packetization buffer
   size is zero bytes, and the NAL units carried in the single RTP
   stream are directly passed to the decoder in their transmission
   order, which is identical to their decoding order.

   When sprop-max-don-diff is greater than 0, the process described in
   the remainder of this section applies.

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

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   Regardless of the buffering state, the receiver stores incoming NAL
   units in reception order into the de-packetization buffer.  NAL units
   carried in RTP packets are stored in the de-packetization buffer
   individually, and the value of AbsDon is calculated and stored for
   each NAL unit.

   Initial buffering lasts until the difference between the greatest and
   smallest AbsDon values of the NAL units in the de-packetization
   buffer is greater than or equal to the value of sprop-max-don-diff.

   After initial buffering, whenever the difference between the greatest
   and smallest AbsDon values of the NAL units in the de-packetization
   buffer is greater than or equal to the value of sprop-max-don-diff,
   the following operation is repeatedly applied until this difference
   is smaller than sprop-max-don-diff:

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

   When no more NAL units are flowing into the de-packetization buffer,
   all NAL units remaining in the de-packetization buffer are removed
   from the buffer and passed to the decoder in the order of increasing
   AbsDon values.

7.  Payload Format Parameters

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

7.1.  Media Type Registration

   The receiver MUST ignore any parameter unspecified in this memo.

   Type name:            video

   Subtype name:         H266

   Required parameters:  none

   Optional parameters:

      profile-id, tier-flag, sub-profile-id, interop-constraints, and
      level-id:

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

         The subset of coding tools that may have been used to generate
         the bitstream or that the receiver supports, as well as some
         additional constraints are indicated collectively by profile-
         id, sub-profile-id, and interop-constraints.

            Informative note: There are 128 values of profile-id.  The
            subset of coding tools identified by the profile-id can be
            further constrained with up to 255 instances of sub-profile-
            id.  In addition, 68 bits included in interop-constraints,
            which can be extended up to 324 bits provide means to
            further restrict tools from existing profiles.  To be able
            to support this fine-granular signalling of coding tool
            subsets with profile-id, sub-profile-id and interop-
            constraints, it would be safe to require symmetric use of
            these parameters in SDP offer/answer unless recv-ols-id is
            included in the SDP answer for choosing one of the layers
            offered.

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

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

         o  The tier-flag, profile-id, sub-profile-id, and interop-
            constraints parameters MUST be used symmetrically, i.e., the
            value of each of these parameters in the offer MUST be the
            same as that in the answer, either explicitly signaled or
            implicitly inferred.

         o  The level-id parameter is changeable as long as the highest
            level indicated by the answer is either equal to or lower
            than that in the offer.  Note that a highest level higher
            than level-id in the offer for receiving can be included as
            max-recv-level-id.

         In SDP offer/answer, when the SDP answer does include the recv-
         ols-id parameter that is less than the sprop-ols-id parameter
         in the SDP offer, the set of tier- flag, profile-id, sub-

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         profile-id, interop-constraints, and level-id parameters
         included in the answer MUST be consistent with that for the
         chosen output layer set as indicated in the SDP offer, with the
         exception that the level-id parameter in the SDP answer is
         changeable as long as the highest level indicated by the answer
         is either lower than or equal to that in the offer.

         More specifications of these parameters, including how they
         relate to syntax elements specified in [VVC] are provided
         below.

      profile-id:

         When profile-id is not present, a value of 1 (i.e., the Main 10
         profile) MUST be inferred.

         When used to indicate properties of a bitstream, profile-id is
         derived from the general_profile_idc syntax element that
         applies to the bitstream in an instance of the
         profile_tier_level( ) syntax structure.

         VVC bitstreams transported over RTP using the technologies of
         this memo SHOULD contain only a single PTL structure in the
         DCI, unless the sender can assure that a receiver can correctly
         decode the the VVC bitstream regardless of what PTL structure
         was used in the SDP O/A exchange.

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         As specified in [VVC], a profile_tier_level( ) syntax structure
         may be contained in an SPS NAL unit, and one or more
         profile_tier_level( ) syntax structures may be contained in a
         VPS NAL unit and in a DCI NAL unit.  One of the following three
         cases applies to the container NAL unit of the
         profile_tier_level( ) syntax structure containing those PTL
         syntax elements used to derive the values of profile-id, tier-
         flag, level-id, sub-profile-id, or interop-constraints: 1) The
         container NAL unit is an SPS, the bitstream is a single-layer
         bitstream, and the profile_tier_level( ) syntax structures in
         all SPSs referenced by the CVSs in the bitstream has the same
         values respectively for those PTL syntax elements; 2) The
         container NAL unit is a VPS, the profile_tier_level( ) syntax
         structure is the one in the VPS that applies to the OLS
         corresponding to the bitstream, and the profile_tier_level( )
         syntax structures applicable to the OLS corresponding to the
         bitstream in all VPSs referenced by the CVSs in the bitstream
         have the same values respectively for those PTL syntax
         elements; 3) The container NAL unit is a DCI NAL unit and the
         profile_tier_level( ) syntax structures in all DCI NAL units in
         the bitstream has the same values respectively for those PTL
         syntax elements.

         [VVC] allows for multiple profile_tier_level( ) structures in a
         DCI NAL unit, which may contain different values for the syntax
         elements used to derive the values of profile-id, tier-flag,
         level-id, sub-profile-id, or interop-constraints in the
         different entries.  However, herein defined is only a single
         profile-id, tier-flag, level-id, sub-profile-id, or interop-
         constraints.  When signaling these parameters, when a DCI NAL
         unit is present with multiple profile_tier_level( ) structures,
         these values SHOULD be the same as the first profile_tier_level
         structure in the DCI, unless the sender has ensured that the
         receiver can decode the bitstream when a different value is
         chosen.

      tier-flag, level-id:

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

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

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

         If no tier-flag is present, a value of 0 MUST be inferred; if
         no level-id is present, a value of 51 (i.e., level 3.1) MUST be
         inferred.

            Informative note: The level values currently defined in the
            VVC specification are in the form of "majorNum.minorNum",
            and the value of the level-id for each of the levels is
            equal to majorNum * 16 + minorNum * 3.  It is expected that
            if any level are defined in the future, the same convention
            will be used, but this cannot be guaranteed.

         When used to indicate properties of a bitstream, the tier-flag
         and level-id parameters are derived respectively from the
         syntax element general_tier_flag, and the syntax element
         general_level_idc or sub_layer_level_idc[j], that apply to the
         bitstream, in an instance of the profile_tier_level( ) syntax
         structure.

         If the tier-flag and level-id are derived from the
         profile_tier_level( ) syntax structure in a DCI NAL unit, the
         following applies:

         o  tier-flag = general_tier_flag

         o  level-id = general_level_idc

         Otherwise, if the tier-flag and level-id are derived from the
         profile_tier_level( ) syntax structure in an SPS or VPS NAL
         unit, and the bitstream contains the highest sublayer
         representation in the OLS corresponding to the bitstream, the
         following applies:

         o  tier-flag = general_tier_flag

         o  level-id = general_level_idc

         Otherwise, if the tier-flag and level-id are derived from the
         profile_tier_level( ) syntax structure in an SPS or VPS NAL
         unit, and the bitstream does not contains the highest sublayer

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         representation in the OLS corresponding to the bitstream, the
         following applies, with j being the value of the sprop-
         sublayer-id parameter:

         o  tier-flag = general_tier_flag

         o  level-id = sub_layer_level_idc[j]

      sub-profile-id:

         The value of the parameter is a comma-separated (',') list of
         data using base64 [RFC4648] representation.

         When used to indicate properties of a bitstream, sub-profile-id
         is derived from each of the ptl_num_sub_profiles
         general_sub_profile_idc[i] syntax elements that apply to the
         bitstream in an profile_tier_level( ) syntax structure.

      interop-constraints:

         A base64 [RFC4648] representation of the data that includes the
         syntax elements ptl_frame_only_constraint_flag and
         ptl_multilayer_enabled_flag and the general_constraints_info( )
         syntax structure that apply to the bitstream in an instance of
         the profile_tier_level( ) syntax structure.

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

         o  ptl_frame_only_constraint_flag = 1

         o  ptl_multilayer_enabled_flag = 0

         o  gci_present_flag in the general_constraints_info( ) syntax
            structure = 0

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

      sprop-sublayer-id:

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

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

      sprop-ols-id:

         This parameter MAY be used to indicate the OLS that the
         bitstream applies to.  When not present, the value of sprop-
         ols-id is inferred to be equal to TargetOlsIdx as specified in
         8.1.1 in [VVC].  If this optional parameter is present, sprop-
         vps MUST also be present or its content MUST be known a priori
         at the receiver.

         The value of sprop-ols-id MUST be in the range of 0 to 256,
         inclusive.

            Informative note: VVC allows having up to 258 output layer
            sets indicated in the VPS as the number of output layer sets
            minus 2 is indicated with a field of 8 bits.

      recv-sublayer-id:

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

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

      recv-ols-id:

         This parameter MAY be used to signal a receiver's choice of the
         offered or declared output layer sets in the sprop-vps.  The
         value of recv-ols-id indicates the OLS index of the bitstream
         that a receiver supports.  When not present, the value of recv-
         ols-id is inferred to be equal to value of the sprop-ols-id
         parameter inferred from or indicated in the SDP offer.  When
         present, the value of recv-ols-id must be included only when
         sprop-ols-id was received and must refer to an output layer set
         in the VPS that includes no layers other than all or a subset
         of the layers of the OLS referred to by sprop-ols-id.  If this
         optional parameter is present, sprop-vps must have been
         received or its content must be known a priori at the receiver.

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         The value of recv-ols-id MUST be in the range of 0 to 257,
         inclusive.

      max-recv-level-id:

         This parameter MAY be used to indicate the highest level a
         receiver supports.

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

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

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

      sprop-dci:

         This parameter MAY be used to convey a decoding capability
         information NAL unit of the bitstream for out-of-band
         transmission.  The parameter MAY also be used for capability
         exchange.  The value of the parameter a base64 [RFC4648]
         representations of the decoding capability information NAL unit
         as specified in Section 7.3.2.1 of [VVC].

      sprop-vps:

         This parameter MAY be used to convey any video parameter set
         NAL unit of the bitstream for out-of-band transmission of video
         parameter sets.  The parameter MAY also be used for capability
         exchange and to indicate sub-stream characteristics (i.e.,
         properties of output layer sets and sublayer representations as
         defined in [VVC]).  The value of the parameter is a comma-
         separated (',') list of base64 [RFC4648] representations of the
         video parameter set NAL units as specified in Section 7.3.2.3
         of [VVC].

         The sprop-vps parameter MAY contain one or more than one video
         parameter set NAL units.  However, all other video parameter
         sets contained in the sprop-vps parameter MUST be consistent
         with the first video parameter set in the sprop-vps parameter.
         A video parameter set vpsB is said to be consistent with
         another video parameter set vpsA if the number of OLSs in vpsA
         and vpsB is the same and any decoder that conforms to the
         profile, tier, level, and constraints indicated by the data
         starting from the syntax element general_profile_idc to the
         syntax structure general_constraints_info(), inclusive, in the

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         profile_tier_level( ) syntax structure corresponding to any OLS
         with index olsIdx in vpsA can decode any CVS(s) referencing
         vpsB when TargetOlsIdx is equal to olsIdx that conforms to the
         profile, tier, level, and constraints indicated by the data
         starting from the syntax element general_profile_idc to the
         syntax structure general_constraints_info(), inclusive, in the
         profile_tier_level( ) syntax structure corresponding to the OLS
         with index TargetOlsIdx in vpsB.

      sprop-sps:

         This parameter MAY be used to convey sequence parameter set NAL
         units of the bitstream for out-of-band transmission of sequence
         parameter sets.  The value of the parameter is a comma-
         separated (',') list of base64 [RFC4648] representations of the
         sequence parameter set NAL units as specified in
         Section 7.3.2.4 of [VVC].

         A sequence parameter set spsB is said to be consistent with
         another sequence parameter set spsA if any decoder that
         conforms to the profile, tier, level, and constraints indicated
         by the data starting from the syntax element
         general_profile_idc to the syntax structure
         general_constraints_info(), inclusive, in the
         profile_tier_level( ) syntax structure in spsA can decode any
         CLVS(s) referencing spsB that conforms to the profile, tier,
         level, and constraints indicated by the data starting from the
         syntax element general_profile_idc to the syntax structure
         general_constraints_info(), inclusive, in the
         profile_tier_level( ) syntax structure in spsB.

      sprop-pps:

         This parameter MAY be used to convey picture parameter set NAL
         units of the bitstream for out-of-band transmission of picture
         parameter sets.  The value of the parameter is a comma-
         separated (',') list of base64 [RFC4648] representations of the
         picture parameter set NAL units as specified in Section 7.3.2.5
         of [VVC].

      sprop-sei:

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

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

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

            1) In an environment where the bitstream was created from
            film-based source material, and no splicing is going to
            occur during the lifetime of the session, the film grain
            characteristics SEI message is likely meaningful, and
            sending it in sprop-sei rather than in the bitstream at each
            entry point may help with saving bits and allows one to
            configure the renderer only once, avoiding unwanted
            artifacts.

            2) Examples for SEI messages that would be meaningless to be
            conveyed in sprop-sei include the decoded picture hash SEI
            message (it is close to impossible that all decoded pictures
            have the same hashtag) or the filler payload SEI message (as
            there is no point in just having more bits in SDP).

      max-lsr:

         The max-lsr MAY be used to signal the capabilities of a
         receiver implementation and MUST NOT be used for any other
         purpose.  The value of max-lsr is an integer indicating the
         maximum processing rate in units of luma samples per second.
         The max-lsr parameter signals that the receiver is capable of
         decoding video at a higher rate than is required by the highest
         level.

            Informative note: When the OPTIONAL media type parameters
            are used to signal the properties of a bitstream, and max-
            lsr is not present, the values of tier-flag, profile-id,
            sub-profile-id interop-constraints, and level-id must always
            be such that the bitstream complies fully with the specified
            profile, tier, and level.

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         When max-lsr is signaled, the receiver MUST be able to decode
         bitstreams that conform to the highest level, with the
         exception that the MaxLumaSr value in Table 136 of [VVC] for
         the highest level is replaced with the value of max-lsr.
         Senders MAY use this knowledge to send pictures of a given size
         at a higher picture rate than is indicated in the highest
         level.

         When not present, the value of max-lsr is inferred to be equal
         to the value of MaxLumaSr given in Table 136 of [VVC] for the
         highest level.

         The value of max-lsr MUST be in the range of MaxLumaSr to 16 *
         MaxLumaSr, inclusive, where MaxLumaSr is given in Table 136 of
         [VVC] for the highest level.

      max-fps:

         The value of max-fps is an integer indicating the maximum
         picture rate in units of pictures per 100 seconds that can be
         effectively processed by the receiver.  The max-fps parameter
         MAY be used to signal that the receiver has a constraint in
         that it is not capable of processing video effectively at the
         full picture rate that is implied by the highest level and,
         when present, max-lsr.

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

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

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

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

      sprop-max-don-diff:

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         If there is no NAL unit naluA that is followed in transmission
         order by any NAL unit preceding naluA in decoding order (i.e.,
         the transmission order of the NAL units is the same as the
         decoding order), the value of this parameter MUST be equal to
         0.

         Otherwise, this parameter specifies the maximum absolute
         difference between the decoding order number (i.e., AbsDon)
         values of any two NAL units naluA and naluB, where naluA
         follows naluB in decoding order and precedes naluB in
         transmission order.

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

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

      sprop-depack-buf-bytes:

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

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

         When sprop-max-don-diff is present and greater than 0, this
         parameter MUST be present and the value MUST be greater than 0.
         When not present, the value of sprop-depack-buf-bytes is
         inferred to be equal to 0.

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

      depack-buf-cap:

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

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

            Informative note: depack-buf-cap indicates the maximum
            possible size of the de-packetization buffer of the receiver
            only, without allowing for network jitter.

7.2.  SDP Parameters

   The receiver MUST ignore any parameter unspecified in this memo.

7.2.1.  Mapping of Payload Type Parameters to SDP

   The media type video/H266 string is mapped to fields in the Session
   Description Protocol (SDP) [RFC4566] as follows:

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

   *  The encoding name in the "a=rtpmap" line of SDP MUST be H266 (the
      media subtype).

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

   *  The OPTIONAL parameters profile-id, tier-flag, sub-profile-id,
      interop-constraints, level-id, sprop-sublayer-id, sprop-ols-id,
      recv-sublayer-id, recv-ols-id, max-recv-level-id, max-lsr, max-
      fps, sprop-max-don-diff, sprop-depack-buf-bytes and depack-buf-
      cap, when present, MUST be included in the "a=fmtp" line of SDP.
      This parameter is expressed as a media type string, in the form of
      a semicolon-separated list of parameter=value pairs.

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

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   An example of media representation in SDP is as follows:

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

7.2.2.  Usage with SDP Offer/Answer Model

   This section describes the negotiation of unicast messages using the
   offer-answer model as described in [RFC3264] and its updates.  The
   section is split into subsections, covering a) media format
   configurations not involving non-temporal scalability; b) scalable
   media format configurations; c) the description of the use of those
   parameters not involving the media configuration itself but rather
   the parameters of the payload format design; and d) multicast.

7.2.2.1.  Non-scalable media format configuration

   A non-scalable VVC media configuration is such a configuration where
   no non-temporal scalability mechanisms are allowed.  In [VVC] version
   1, that implies that general_profile_idc indicates one of the
   following profiles: Main10, Main10 still, Main 10 4:4:4, Main10 4:4:4
   still, with general_profile_dic values of 1, 65, 33, and 97,
   respectively.  Note that non-scalable media configurations includes
   temporal scalability, inline with VVC's design philosophy and profile
   structure.

   The following limitations and rules pertaining to the media
   configuration apply:

   *  The parameters identifying a media format configuration for VVC
      are profile-id, tier-flag, sub-profile-id, level-id, and interop-
      constraints.  These media configuration parameters, except level-
      id, MUST be used symmetrically.

      The answerer MUST structure its answer in according to one of the
      following three options:

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

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      2) include in the answer the recv-sublayer-id parameter, with a
      value less than the sprop-sublayer-id parameter in the offer, for
      the media format (payload type), and maintain all configuration
      parameters with the values remaining the same as in the offer for
      the media format (payload type), with the exception that the value
      of level-id is changeable as long as the highest level indicated
      by the answer is not higher than the level indicated by the sprop-
      sps or sprop-vps in offer for the chosen sublayer representation;
      or

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

            Informative note: The above requirement for symmetric use
            does not apply for level-id, and does not apply for the
            other bitstream or RTP stream properties and capability
            parameters as described in Section 7.2.2.3 below.

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

   *  The same RTP payload type number used in the offer for the media
      subtype H266 MUST be used in the answer when the answer includes
      recv-sublayer-id.  When the answer does not include recv-sublayer-
      id, the answer MUST NOT contain a payload type number used in the
      offer for the media subtype H266 unless the configuration is
      exactly the same as in the offer or the configuration in the
      answer only differs from that in the offer with a different value
      of level-id.  The answer MAY contain the recv-sublayer-id
      parameter if an VVC bitstream contains multiple operation points
      (using temporal scalability and sublayers) and sprop-sps or sprop-
      vps is included in the offer where information of sublayers are
      present in the first sequence parameter set or video parameter set
      contained in sprop-sps or sprop-vps respectively.  If the sprop-
      sps or sprop-vps is provided in an offer, an answerer MAY select a
      particular operation point indicated in the first sequence
      parameter set or video parameter set contained in sprop-sps or
      sprop-vps respectively.  When the answer includes a recv-sublayer-
      id that is less than a sprop-sublayer-id in the offer, the
      following applies:

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      1) When sprop-sps parameter is present, all sequence parameter
      sets contained in the sprop-sps parameter in the SDP answer and
      all sequence parameter sets sent in-band for either the offerer-
      to-answerer direction or the answerer-to-offerer direction MUST be
      consistent with the first sequence parameter set in the sprop-sps
      parameter of the offer (see the semantics of sprop-sps in
      Section 7.1 of this document on one sequence parameter set being
      consistent with another sequence parameter set).

      2) When sprop-vps parameter is present, all video parameter sets
      contained in the sprop-vps parameter in the SDP answer and all
      video parameter sets sent in-band for either the offerer-to-
      answerer direction or the answerer-to-offerer direction MUST be
      consistent with the first video parameter set in the sprop-vps
      parameter of the offer (see the semantics of sprop-vps in
      Section 7.1 of this document on one video parameter set being
      consistent with another video parameter set).

      3) The bitstream sent in either direction MUST conform to the
      profile, tier, level, and constraints of the chosen sublayer
      representation as indicated by the profile_tier_level( ) syntax
      structure in the first sequence parameter set in the sprop-sps
      parameter or by the first profile_tier_level( ) syntax structure
      in the first video parameter set in the sprop-vps parameter of the
      offer.

            Informative note: When an offerer receives an answer that
            does not include recv-sublayer-id, it has to compare payload
            types not declared in the offer based on the media type
            (i.e., video/H266) and the above media configuration
            parameters with any payload types it has already declared.
            This will enable it to determine whether the configuration
            in question is new or if it is equivalent to configuration
            already offered, since a different payload type number may
            be used in the answer.  The ability to perform operation
            point selection enables a receiver to utilize the temporal
            scalable nature of an VVC bitstream.

7.2.2.2.  Scalable media format configuration

   A scalable VVC media configuration is such a configuration where non-
   temporal scalability mechanisms are allowed.  In [VVC] version 1,
   that implies that general_profile_idc indicates one of the following
   profiles: Multilayer Main 10, and Multilayer Main 10 4:4:4, with
   general_profile_idc values of 17 and 49, respectively.

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   The following limitations and rules pertaining to the media
   configuration apply.  They are listed in an order that would be
   logical for an implementation to follow:

   *  The parameters identifying a media format configuration for
      scalable VVC are profile-id, tier-flag, sub-profile-id, level-id,
      interop-constraints, and sprop-vps.  These media configuration
      parameters, except level-id, MUST be used symmetrically, except as
      noted below.

   *  The answerer MAY include a level-id that MUST be lower or equal
      than the level-id indicated in the offer (either expressed by
      level-id in the offer, or implied by the default level as specific
      in Section 7.1).

   *  The offerer MUST include sprop-vps including at least one valid
      VPS, so to allow the answerer to meaningfully interpret sprop-ols-
      id and select recv-ols-id (see below).

   *  The offerer MUST include sprop-ols-id.  The answerer MUST include
      recv-ols-id, and recv-ols-id MUST indicate a supported output
      layer set in the same dependency tree as sprop-ols-id.  If unable,
      the answerer MUST remove the media format.

         Informative note: if an offerer wants to offer more than one
         output layer set, in can do so by offering multiple VVC media
         with different payload types.

   *  The offerer MAY include sprop-sublayer-id which, in case of
      scalable VVC, is interpreted as the highest sublayer of the
      highest enhancement layer in the OLS indicated by sprop-ols-id.
      The answerer MAY include recv-sublayer-id which can be used to
      downgrade the sublayer of the highest enhancement layer.  This
      specification does not support downgrading the sublayer of any
      layers in the OLS that are not the highest layer.

   Editor-note-3: Miska agrees to provide text.  Currently we agreed to
   use Stephan's option 1 which normatively disallow the O/A process to
   arrive at signalling sublayer information.

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         Informative note: in other words, using this mechanism, an
         answerer can downgrade only the frame rate for the highest
         spatial/quality layer (typically corresponding to the highest
         resolution or bitrate, hence the most complex to decode), but
         not for lower spatial/quality layers.  The answerer must
         support all sublayers for lower layers in the OLS, or reject
         the offer.  That's not a big burden, as the receiver/decoder
         has the option to discard any sublayers it cannot decode,
         irrespective of what is being signalled through offer/answer.

   *  The answerer MUST maintain all configuration parameters with the
      values being the same as signaled in the sprop-vps for the
      operating point with the largest number of sublayers for the
      chosen output layer set, with the exception that the value of
      level-id is changeable as long as the highest level indicated by
      the answer is not higher than the level indicated by the sprop-vps
      in offer for the operating point with the largest number of
      sublayers for the chosen output layer set.

7.2.2.3.  Payload format configuration

   The following limitations and rules pertain to the configuration of
   the payload format mechanisms---buffer management mostly and apply to
   both scalable and non-scalable VVC.

   *  The parameters sprop-max-don-diff, and sprop-depack-buf-bytes
      describe the properties of an RTP stream that the offerer or the
      answerer is sending for the media format configuration.  This
      differs from the normal usage of the offer/answer parameters:
      normally such parameters declare the properties of the bitstream
      or RTP stream that the offerer or the answerer is able to receive.
      When dealing with VVC, the offerer assumes that the answerer will
      be able to receive media encoded using the configuration being
      offered.

         Informative note: The above parameters apply for any RTP
         stream, when present, sent by a declaring entity with the same
         configuration.  In other words, the applicability of the above
         parameters to RTP streams depends on the source endpoint.
         Rather than being bound to the payload type, the values may
         have to be applied to another payload type when being sent, as
         they apply for the configuration.

   *  The capability parameter max-lsr MAY be used to declare further
      capabilities of the offerer or answerer for receiving.  It MUST
      NOT be present when the direction attribute is sendonly.

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

   *  When an offerer offers an interleaved stream, indicated by the
      presence of sprop-max-don-diff with a value larger than zero, the
      offerer MUST include the size of the de-packetization buffer
      sprop-depack-buf-bytes.

   *  To enable the offerer and answerer to inform each other about
      their capabilities for de-packetization buffering in receiving RTP
      streams, both parties are RECOMMENDED to include depack-buf-cap.

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

   *  The answerer MAY use either out-of-band or in-band transport of
      parameter sets for the bitstream it is sending, regardless of
      whether out-of-band parameter sets transport has been used in the
      offerer-to-answerer direction.  Parameter sets included in an
      answer are independent of those parameter sets included in the
      offer, as they are used for decoding two different bitstreams, one
      from the answerer to the offerer and the other in the opposit
      direction.  In case some RTP packets are sent before the SDP
      offer/answer settles down, in-band parameter sets MUST be used for
      those RTP stream parts sent before the SDP offer/answer.

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

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

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

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

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

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

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

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

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

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                                       sendonly --+
               answer: recvonly, recv-ols-id --+  |
                 recvonly w/o recv-ols-id --+  |  |
         answer: sendrecv, recv-ols-id --+  |  |  |
           sendrecv w/o recv-ols-id --+  |  |  |  |
                                      |  |  |  |  |
   profile-id                         C  D  C  D  P
   tier-flag                          C  D  C  D  P
   level-id                           D  D  D  D  P
   sub-profile-id                     C  D  C  D  P
   interop-constraints                C  D  C  D  P
   max-recv-level-id                  R  R  R  R  -
   sprop-max-don-diff                 P  P  -  -  P
   sprop-depack-buf-bytes             P  P  -  -  P
   depack-buf-cap                     R  R  R  R  -
   max-lsr                            R  R  R  R  -
   max-fps                            R  R  R  R  -
   sprop-dci                          P  P -  -  P
   sprop-sei                          P  P -  -  P
   sprop-vps                          P  P  -  -  P
   sprop-sps                          P  P  -  -  P
   sprop-pps                          P  P  -  -  P
   sprop-sublayer-id                 P  P  -  -  P
   recv-sublayer-id                  O  O  O  O  -
   sprop-ols-id                       P  P  -  -  P
   recv-ols-id                        X  O  X  O  -

   Legend:

    C: configuration for sending and receiving bitstreams
    D: changeable configuration, same as C except possible
       to answer with a different but consistent value (see the
       semantics of the six parameters related to profile, tier,
       and level on these parameters being consistent)
    P: properties of the bitstream to be sent
    R: receiver capabilities
    O: operation point selection
    X: MUST NOT be present
    -: not usable, when present MUST be ignored

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

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

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

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

   An answerer MAY extend the offer with additional media format
   configurations.  However, to enable their usage, in most cases a
   second offer is required from the offerer to provide the bitstream
   property parameters that the media sender will use.  This also has
   the effect that the offerer has to be able to receive this media
   format configuration, not only to send it.

7.2.2.4.  Multicast

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

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

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

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

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

7.2.3.  Usage in Declarative Session Descriptions

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

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

      -  Declaring actual configuration or bitstream properties:

         o  profile-id

         o  tier-flag

         o  level-id

         o  interop-constraints

         o  sub-profile-id

         o  sprop-dci

         o  sprop-vps

         o  sprop-sps

         o  sprop-pps

         o  sprop-max-don-diff

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         o  sprop-depack-buf-bytes

         o  sprop-sublayer-id

         o  sprop-ols-id

         o  sprop-sei

      -  Not usable (when present, they MUST be ignored):

         o  max-lsr

         o  max-fps

         o  max-recv-level-id

         o  depack-buf-cap

         o  recv-sublayer-id

         o  recv-ols-id

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

7.2.4.  Considerations for Parameter Sets

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

8.  Use with Feedback Messages

   The following subsections define the use of the Picture Loss
   Indication (PLI) and Full Intra Request (FIR) feedback messages with
   [VVC].  The PLI is defined in [RFC4585], and the FIR message is
   defined in [RFC5104].  In accordance with this memo, unlike [HEVC], a
   sender MUST NOT send Slice Loss Indication (SLI) or Reference Picture
   Selection Indication (RPSI), and a receiver SHOULD ignore RPSI and
   treat a received SLI as a PLI.

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8.1.  Picture Loss Indication (PLI)

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

8.2.  Full Intra Request (FIR)

   The purpose of the FIR message is to force an encoder to send an
   independent decoder refresh point as soon as possible, while
   observing applicable congestion-control-related constraints, such as
   those set out in [RFC8082]).

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

9.  Security Considerations

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

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

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550] , and in any applicable RTP profile such as
   RTP/AVP [RFC3551] , RTP/AVPF [RFC4585] , RTP/SAVP [RFC3711] , or RTP/
   SAVPF [RFC5124] .  However, as "Securing the RTP Framework: Why RTP
   Does Not Mandate a Single Media Security Solution" [RFC7202]
   discusses, it is not an RTP payload format's responsibility to
   discuss or mandate what solutions are used to meet the basic security
   goals like confidentiality, integrity and source authenticity for RTP
   in general.  This responsibility lays on anyone using RTP in an
   application.  They can find guidance on available security mechanisms
   and important considerations in "Options for Securing RTP Sessions"
   [RFC7201] . The rest of this section discusses the security impacting
   properties of the payload format itself.

   Because the data compression used with this payload format is applied
   end-to-end, any encryption needs to be performed after compression.
   A potential denial-of-service threat exists for data encodings using
   compression techniques that have non-uniform receiver-end
   computational load.  The attacker can inject pathological datagrams
   into the bitstream that are complex to decode and that cause the
   receiver to be overloaded.  [VVC] is particularly vulnerable to such
   attacks, as it is extremely simple to generate datagrams containing
   NAL units that affect the decoding process of many future NAL units.
   Therefore, the usage of data origin authentication and data integrity
   protection of at least the RTP packet is RECOMMENDED, for example,
   with SRTP [RFC3711] .

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

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   End-to-end security with authentication, integrity, or
   confidentiality protection will prevent a MANE from performing media-
   aware operations other than discarding complete packets.  In the case
   of confidentiality protection, it will even be prevented from
   discarding packets in a media-aware way.  To be allowed to perform
   such operations, a MANE is required to be a trusted entity that is
   included in the security context establishment.

10.  Congestion Control

   Congestion control for RTP SHALL be used in accordance with RTP
   [RFC3550] and with any applicable RTP profile, e.g., AVP [RFC3551].
   If best-effort service is being used, an additional requirement is
   that users of this payload format MUST monitor packet loss to ensure
   that the packet loss rate is within an acceptable range.  Packet loss
   is considered acceptable if a TCP flow across the same network path,
   and experiencing the same network conditions, would achieve an
   average throughput, measured on a reasonable timescale, that is not
   less than all RTP streams combined are achieving.  This condition can
   be satisfied by implementing congestion-control mechanisms to adapt
   the transmission rate, the number of layers subscribed for a layered
   multicast session, or by arranging for a receiver to leave the
   session if the loss rate is unacceptably high.

   The bitrate adaptation necessary for obeying the congestion control
   principle is easily achievable when real-time encoding is used, for
   example, by adequately tuning the quantization parameter.  However,
   when pre-encoded content is being transmitted, bandwidth adaptation
   requires the pre-coded bitstream to be tailored for such adaptivity.
   The key mechanisms available in [VVC] are temporal scalability, and
   spatial/SNR scalability.  A media sender can remove NAL units
   belonging to higher temporal sublayers (i.e., those NAL units with a
   high value of TID) or higher spatio-SNR layers until the sending
   bitrate drops to an acceptable range.

   The mechanisms mentioned above generally work within a defined
   profile and level and, therefore, no renegotiation of the channel is
   required.  Only when non-downgradable parameters (such as profile)
   are required to be changed does it become necessary to terminate and
   restart the RTP stream(s).  This may be accomplished by using
   different RTP payload types.

   MANEs MAY remove certain unusable packets from the RTP stream when
   that RTP stream was damaged due to previous packet losses.  This can
   help reduce the network load in certain special cases.  For example,
   MANES can remove those FUs where the leading FUs belonging to the
   same NAL unit have been lost or those dependent slice segments when
   the leading slice segments belonging to the same slice have been

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   lost, because the trailing FUs or dependent slice segments are
   meaningless to most decoders.  MANES can also remove higher temporal
   scalable layers if the outbound transmission (from the MANE's
   viewpoint) experiences congestion.

11.  IANA Considerations

   Placeholder

12.  Acknowledgements

   Dr. Byeongdoo Choi is thanked for the video codec related technical
   discussion and other aspects in this memo.  Xin Zhao and Dr. Xiang Li
   are thanked for their contributions on [VVC] specification
   descriptive content.  Spencer Dawkins is thanked for his valuable
   review comments that led to great improvements of this memo.  Some
   parts of this specification share text with the RTP payload format
   for HEVC [RFC7798].  We thank the authors of that specification for
   their excellent work.

13.  References

13.1.  Normative References

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

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

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

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

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

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

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

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

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

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

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

   [RFC5576]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific
              Media Attributes in the Session Description Protocol
              (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
              <https://www.rfc-editor.org/info/rfc5576>.

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

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

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

   [VSEI]     "Versatile supplemental enhancement information messages
              for coded video bitstreams", 2020,
              <http://handle.itu.int/11.1002/1000/14337>.

   [VVC]      "Versatile Video Coding, ITU-T Recommendation H.266",
              2020, <http://handle.itu.int/11.1002/1000/14336>.

13.2.  Informative References

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

   [HEVC]     "High efficiency video coding, ITU-T Recommendation
              H.265", 2019, <http://handle.itu.int/11.1002/1000/14107>.

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

   [RFC2326]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
              Streaming Protocol (RTSP)", RFC 2326,
              DOI 10.17487/RFC2326, April 1998,
              <https://www.rfc-editor.org/info/rfc2326>.

   [RFC2974]  Handley, M., Perkins, C., and E. Whelan, "Session
              Announcement Protocol", RFC 2974, DOI 10.17487/RFC2974,
              October 2000, <https://www.rfc-editor.org/info/rfc2974>.

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

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

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

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

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

Appendix A.  Change History

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

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

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

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

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

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

   draft-ietf-payload-rtp-vvc-04 ........ VVC coding tool introduction
   update

   draft-ietf-payload-rtp-vvc-05 ........ reference udpate and adding
   placement for open issues

   draft-ietf-payload-rtp-vvc-06 ........ address editor's note

   draft-ietf-payload-rtp-vvc-07 ........ address editor's notes

   draft-ietf-payload-rtp-vvc-08 ........ address editor's notes

   draft-ietf-payload-rtp-vvc-09 ........ address editor's notes

   draft-ietf-payload-rtp-vvc-10 ........ address editor's notes

Authors' Addresses

Zhao, et al.              Expires 28 April 2022                [Page 64]
Internet-Draft         RTP payload format for VVC           October 2021

   Shuai Zhao
   Tencent
   2747 Park Blvd
   Palo Alto,  94588
   United States of America

   Email: shuai.zhao@ieee.org

   Stephan Wenger
   Tencent
   2747 Park Blvd
   Palo Alto,  94588
   United States of America

   Email: stewe@stewe.org

   Yago Sanchez
   Fraunhofer HHI
   Einsteinufer 37
   10587 Berlin
   Germany

   Email: yago.sanchez@hhi.fraunhofer.de

   Ye-Kui Wang
   Bytedance Inc.
   8910 University Center Lane
   San Diego,  92122
   United States of America

   Email: yekui.wang@bytedance.com

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