[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: 00 01 draft-ietf-payload-vp9

Payload Working Group                                          J. Uberti
Internet-Draft                                                 S. Holmer
Intended status: Standards Track                              M. Flodman
Expires: September 10, 2015                                       Google
                                                               J. Lennox
                                                                 D. Hong
                                                                   Vidyo
                                                           March 9, 2015


                    RTP Payload Format for VP9 Video
                      draft-uberti-payload-vp9-01

Abstract

   This memo describes an RTP payload format for the VP9 video codec.
   The payload format has wide applicability, as it supports
   applications from low bit-rate peer-to-peer usage, to high bit-rate
   video conferences.  It includes provisions for temporal and spatial
   scalability.

Status of This Memo

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

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

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

   This Internet-Draft will expire on September 10, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



Uberti, et al.         Expires September 10, 2015               [Page 1]


Internet-Draft         RTP Payload Format for VP9             March 2015


   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions, Definitions and Acronyms . . . . . . . . . . . .   2
   3.  Media Format Description  . . . . . . . . . . . . . . . . . .   3
   4.  Payload Format  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  RTP Header Usage  . . . . . . . . . . . . . . . . . . . .   4
     4.2.  VP9 Payload Description . . . . . . . . . . . . . . . . .   6
       4.2.1.  Scalability Structure (SS): . . . . . . . . . . . . .  10
     4.3.  VP9 Payload Header  . . . . . . . . . . . . . . . . . . .  12
     4.4.  Frame Fragmentation . . . . . . . . . . . . . . . . . . .  12
     4.5.  Examples of VP9 RTP Stream  . . . . . . . . . . . . . . .  12
   5.  Using VP9 with RPSI and SLI Feedback  . . . . . . . . . . . .  12
     5.1.  RPSI  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     5.2.  SLI . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.3.  Example . . . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Payload Format Parameters . . . . . . . . . . . . . . . . . .  15
     6.1.  Media Type Definition . . . . . . . . . . . . . . . . . .  15
     6.2.  SDP Parameters  . . . . . . . . . . . . . . . . . . . . .  17
       6.2.1.  Mapping of Media Subtype Parameters to SDP  . . . . .  17
       6.2.2.  Offer/Answer Considerations . . . . . . . . . . . . .  17
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   8.  Congestion Control  . . . . . . . . . . . . . . . . . . . . .  18
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   This memo describes an RTP payload specification applicable to the
   transmission of video streams encoded using the VP9 video codec
   [I-D.grange-vp9-bitstream].  The format described in this document
   can be used both in peer-to-peer and video conferencing applications.

   TODO: VP9 description.  Please see [I-D.grange-vp9-bitstream].

2.  Conventions, Definitions and Acronyms

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





Uberti, et al.         Expires September 10, 2015               [Page 2]


Internet-Draft         RTP Payload Format for VP9             March 2015


3.  Media Format Description

   The VP9 codec can maintain up to eight reference frames, of which up
   to three can be referenced or updated by any new frame.

   VP9 also allows a reference frame to be resampled and used as a
   reference for another frame of a different resolution.  This allows
   internal resolution changes without requiring the use of key frames.

   These features together enable an encoder to implement various forms
   of coarse-grained scalability, including temporal, spatial and
   quality scalability modes, as well as combinations of these, without
   the need for explicit scalable coding tools.

   Temporal layers define different frame rates of video; spatial and
   quality layers define different and possibly dependent
   representations of a single input frame.  Spatial layers allow a
   frame to be encoded at different resolutions, whereas quality layers
   allow a frame to be encoded at the same resolution but at different
   qualities (and thus with different amounts of coding error).  VP9
   supports quality layers as spatial layers without any resolution
   changes; hereinafter, the term "spatial layer" is used to represent
   both spatial and quality layers.

   This payload format specification defines how such temporal and
   spatial scalability layers can be described and communicated.

   Layers are designed (and MUST be encoded) such that if any layer, and
   all higher layers, are removed from the bitstream along any of the
   two dimensions, the remaining bitstream is still correctly decodable.

   For terminology, this document uses the term "layer frame" to refer
   to a single encoded VP9 frame for a particular resolution/quality,
   and "super frame" to refer to all the representations (layer frames)
   at a single instant in time.  A super frame thus consists of one or
   more layer frames, encoding different spatial layers.

   Within a super frame, a layer frame with spatial layer ID equal to S,
   where S > 0, can depend on a frame with a lower spatial layer ID.
   This "inter-layer" dependency results in additional coding gain to
   the traditional "inter-picture" dependency, where a frame depends on
   previously coded frame in time.  For simplicity, this payload format
   assumes that, within a super frame if inter-layer dependency is used,
   a spatial layer S frame can only depend on spatial layer S-1 frame
   when S > 0.  Additionally, if inter-picture dependency is used,
   spatial layer S frame is assumed to only depend on prevously coded
   spatial layer S frame.




Uberti, et al.         Expires September 10, 2015               [Page 3]


Internet-Draft         RTP Payload Format for VP9             March 2015


   TODO: Describe how simulcast can be supported?

   Given above simplifications for inter-layer and inter-picture
   dependencies, a flag (the D bit described below) is used to indicate
   whether a spatial layer S frame depends on spatial layer S-1 frame.
   Then a receiver only needs to know the inter-picture dependency
   structure for a given spatial layer frame in order to determine its
   decodability.  Two modes of describing the inter-picture dependency
   structure are possible: "flexible mode" and "non-flexible mode".  An
   encoder can only switch between the two on the very first packet of a
   key frame with temporal layer ID equal to 0.

   In flexible mode, each packet can contain up to 3 reference indices,
   which identifies all frames referenced by the frame transmitted in
   the current packet for inter-picture prediction.  This (along with
   the D bit) enables a receiver to identify if a frame is decodable or
   not and helps it understand the temporal layer structure so that it
   can drop packets as it sees fit.  Since this is signaled in each
   packet it makes it possible to have very flexible temporal layer
   hierarchies and patterns which are changing dynamically.

   In non-flexible mode, the inter-picture dependency (the reference
   indices) of a group of frames (GOF) MUST be pre-specified as part of
   the scalability structure (SS) data.  In this mode, each packet will
   have an index to refer to one of the described frames, from which the
   frames referenced by the frame transmitted in the current packet for
   inter-picture prediction can be identified.

   The SS data can also be used to specify the resolution of each
   spatial layer present in the VP9 stream.

4.  Payload Format

   This section describes how the encoded VP9 bitstream is encapsulated
   in RTP.  To handle network losses usage of RTP/AVPF [RFC4585] is
   RECOMMENDED.  All integer fields in the specifications are encoded as
   unsigned integers in network octet order.

4.1.  RTP Header Usage












Uberti, et al.         Expires September 10, 2015               [Page 4]


Internet-Draft         RTP Payload Format for VP9             March 2015


   The general RTP payload format for VP9 is depicted below.

      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             |
     |                             ....                              |
     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
     |            VP9 payload descriptor (integer #bytes)            |
     :                                                               :
     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               : VP9 pyld hdr  |               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               |
     |                                                               |
     +                                                               |
     :                   Bytes 2..N of VP9 payload                   :
     |                                                               |
     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               :    OPTIONAL RTP padding       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The VP9 payload descriptor and VP9 payload header will be described
   in the next section.  OPTIONAL RTP padding MUST NOT be included
   unless the P bit is set.

                                 Figure 1

   Marker bit (M):  MUST be set to 1 for the final packet of the highest
      spatial layer frame (the final packet of the super frame), and 0
      otherwise.  Unless spatial scalability is in use for this super
      frame, this will have the same value as the E bit described below.
      Note that a MANE MUST set this value to 1 for the target spatial
      layer frame when shaping out higher spatial layers.

   Timestamp:  The RTP timestamp indicates the time when the input frame
      was sampled, at a clock rate of 90 kHz.  If the input frame is
      encoded with multiple layer frames, all of the layer frames of the
      super frame MUST have the same timestamp.

   Sequence number:  The sequence numbers are monotonically increasing
      in order of the encoded bitstream.




Uberti, et al.         Expires September 10, 2015               [Page 5]


Internet-Draft         RTP Payload Format for VP9             March 2015


   The remaining RTP header fields are used as specified in [RFC3550].

4.2.  VP9 Payload Description

   In flexible mode (with the F bit below set to 1), The first octets
   after the RTP header are the VP9 payload descriptor, with the
   following structure.

         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        |I|P|L|F|B|E|V|-| (REQUIRED)
        +-+-+-+-+-+-+-+-+
   I:   |M| PICTURE ID  | (RECOMMENDED)
        +-+-+-+-+-+-+-+-+
   M:   | EXTENDED PID  | (RECOMMENDED)
        +-+-+-+-+-+-+-+-+
   L:   |  T  |U|  S  |D| (CONDITIONALLY RECOMMENDED)
        +-+-+-+-+-+-+-+-+                             -\
   P,F: | P_DIFF    |X|N| (CONDITIONALLY RECOMMENDED)  .
        +-+-+-+-+-+-+-+-+                              . - up to 3 times
   X:   |EXTENDED P_DIFF| (OPTIONAL)                   .
        +-+-+-+-+-+-+-+-+                             -/
   V:   | SS            |
        | ..            |
        +-+-+-+-+-+-+-+-+


                                 Figure 2























Uberti, et al.         Expires September 10, 2015               [Page 6]


Internet-Draft         RTP Payload Format for VP9             March 2015


   In non-flexible mode (with the F bit below set to 0), The first
   octets after the RTP header are the VP9 payload descriptor, with the
   following structure.

         0 1 2 3 4 5 6 7
        +-+-+-+-+-+-+-+-+
        |I|P|L|F|B|E|V|-| (REQUIRED)
        +-+-+-+-+-+-+-+-+
   I:   |M| PICTURE ID  | (RECOMMENDED)
        +-+-+-+-+-+-+-+-+
   M:   | EXTENDED PID  | (RECOMMENDED)
        +-+-+-+-+-+-+-+-+
   L:   |GOF_IDX|  S  |D| (CONDITIONALLY RECOMMENDED)
        +-+-+-+-+-+-+-+-+
        |   TL0PICIDX   | (CONDITIONALLY REQUIRED)
        +-+-+-+-+-+-+-+-+
   V:   | SS            |
        | ..            |
        +-+-+-+-+-+-+-+-+


                                 Figure 3

   I: Picture ID (PID) present.  When set to one, the OPTIONAL PID MUST
      be present after the mandatory first octet and specified as below.
      Otherwise, PID MUST NOT be present.

   P: Inter-picture predicted layer frame.  When set to zero, the layer
      frame does not utilize inter-picture prediction.  In this case,
      up-switching to current spatial layer's frame is possible from
      directly lower spatial layer frame.  P SHOULD also be set to zero
      when encoding a layer synchronization frame in response to an LRR
      [I-D.lennox-avtext-lrr].

   L: Layer indices present.  When set to one, the one or two octets
      following the mandatory first octet and the PID (if present) is as
      described by "Layer indices" below.  If the F bit (described
      below) is set to 1 (indicating flexible mode), then only one octet
      is present for the layer indices.  Otherwise if the F bit is set
      to 0 (indicating non-flexible mode), then two octets are present
      for the layer indices.

   F: Flexible mode.  F set to one indicates flexible mode and if the P
      bit is also set to one, then the octets following the mandatory
      first octet, the PID, and layer indices (if present) are as
      described by "Reference indices" below.  This MUST only be set to
      one if the I bit is also set to one; if the I bit is set to zero,
      then this MUST also be set to zero and ignored by receivers.  The



Uberti, et al.         Expires September 10, 2015               [Page 7]


Internet-Draft         RTP Payload Format for VP9             March 2015


      value of this F bit CAN ONLY CHANGE on the very first packet of a
      key picture.  This is a packet with the P bit equal to zero, S or
      D bit (described below) equal to zero, B bit (described below)
      equal to 1, and temporal layer ID equal to 0.

   B: Start of a layer frame.  MUST be set to 1 if the first payload
      octet of the RTP packet is the beginning of a new VP9 layer frame,
      and MUST NOT be 1 otherwise.  Note that this layer frame might not
      be the very first layer frame of a super frame.

   E: End of a layer frame.  MUST be set to 1 for the final RTP packet
      of a VP9 layer frame, and 0 otherwise.  This enables a decoder to
      finish decoding the layer frame, where it otherwise may need to
      wait for the next packet to explicitly know that the layer frame
      is complete.  Note that, if spatial scalability is in use, more
      layer frames from the same super frame may follow; see the
      description of the M bit above.

   V: Scalability structure (SS) data present.  When set to one, the
      OPTIONAL SS data MUST be present in the payload descriptor.
      Otherwise, the SS data MUST NOT be present.

   -: Bit reserved for future use.  MUST be set to zero and MUST be
      ignored by the receiver.

   The mandatory first octet is followed by the extension data fields
   that are enabled:

   M: The most significant bit of the first octet is an extension flag.
      The field MUST be present if the I bit is equal to one.  If set,
      the PID field MUST contain 15 bits; otherwise, it MUST contain 7
      bits.  See PID below.

   Picture ID (PID):  Picture ID represented in 7 or 15 bits, depending
      on the M bit.  This is a running index of the pictures.  The field
      MUST be present if the I bit is equal to one.  If M is set to
      zero, 7 bits carry the PID; else if M is set to one, 15 bits carry
      the PID.  The sender may choose between 7 or 15 bits index.  The
      PID SHOULD start on a random number, and MUST wrap after reaching
      the maximum ID.  The receiver MUST NOT assume that the number of
      bits in PID stay the same through the session.

   Layer indices:  This information is optional but recommended whenever
      encoding with layers.  In the flexible mode (when the F bit is set
      to 1), one octet is used to specify a layer frame's temporal layer
      ID (T) and spatial layer ID (S) as shown in Figure 2.
      Additionally, a bit (U) is used to indcate that the current frame
      is a "switching up point" frame.  Another bit (D) is used to



Uberti, et al.         Expires September 10, 2015               [Page 8]


Internet-Draft         RTP Payload Format for VP9             March 2015


      indicate whether inter-layer prediction is used for the current
      layer frame.

      In the non-flexible mode (when the F bit is set to 0), two octets
      are used as depicted in Figure 3.  Like the flexible mode, the
      first byte contains the spatial layer ID and the D bit.  Unlike
      the flexible mode, instead of the T and U fields, a group of
      frames index (GOF_IDX) is specified, which can be used to obtain
      the values of T and U fields from the scalable structure (SS) data
      described below.  An additional octet to represent the temporal
      layer 0 index, TL0PICIDX, is present so that all minimally
      required frames can be tracked.

      The T and S fields, whether obtained directly or indirectly from
      the SS data, indicate the temporal and spatial layers and can help
      MCUs measure bitrates per layer and can help them make a quick
      decision on whether to relay a packet or not.  They can also help
      receivers determine what layers they are currently decoding.

      T: The temporal layer ID of current frame.  This field is only
         present in the flexible mode (F = 1).

      U: Switching up point.  This bit is only present in the flexible
         mode (F = 1).  If this bit is set to 1 for the current frame
         with temporal layer ID equal to T, then "switch up" to a higher
         frame rate is possible as subsequent higher temporal layer
         frames will not depend on any frame before the current frame
         (in coding time) with temporal layer ID greater than T.

      S: The spatial layer ID of current frame.  Note that frames with
         spatial layer S > 0 may be dependent on decoded spatial layer
         S-1 frame within the same super frame.

      D: Inter-layer dependency used.  MUST be set to one if current
         spatial layer S frame depends on spatial layer S-1 frame of the
         same super frame.  MUST only be set to zero if current spatial
         layer S frame does not depend on spatial layer S-1 frame of the
         same super frame.  For the base layer frame with S equal to 0,
         this D bit MUST be set to zero.

      GOF_IDX:  An index to a frame in the group of frames (GOF)
         described by the SS data.  This field is only present in the
         non-flexible mode (F = 0).  In this mode, the SS data SHOULD
         have been received and the temporal characteristics of each
         frame must have been speficied as group of frames in the SS
         data (see the description of "Scalability structure" below).
         Here, the values of the T and the U fields are derived from the
         SS data.  Additionally, the frame's inter-picture dependecy can



Uberti, et al.         Expires September 10, 2015               [Page 9]


Internet-Draft         RTP Payload Format for VP9             March 2015


         also be obtained from the SS data.  In the case no SS data has
         been received or the received SS data does not specify GOF (N_G
         is set to 0), then GOF_IDX MUST be ignored and the stream is
         assumed to have no temporal hierarchy with both T and U equal
         to 0.

      TL0PICIDX:  8 bits temporal layer zero index.  TL0PICIDX is only
         present in the non-flexible mode (F = 0).  This is a running
         index for the temporal base layer frames, i.e., the frames with
         temporal layer ID (TID) set to 0.  If TID is larger than 0,
         TL0PICIDX indicates which temporal base layer frame the current
         frame depends on.  TL0PICIDX MUST be incremented when TID is 0.
         The index SHOULD start on a random number, and MUST restart at
         0 after reaching the maximum number 255.

   Reference indices:  These bytes are optional, but recommended when
      encoding with temporal layers in the flexible mode.  When P and F
      are both set to one, then at least one reference index has to be
      specified as below.  Additional reference indices (total of up to
      3 reference indices are allowed) may be specified using the N bit
      below.  When either P or F is set to zero, then no reference index
      is specified.

      P_DIFF:  The reference index specified as the relative PID from
         the current frame.  For example, when P_DIFF=3 on a packet
         containing the frame with PID 112 means that the frame refers
         back to the frame with PID 109.  This calculation is done
         modulo the size of the PID field, i.e., either 7 or 15 bits.
         For most layer structures a 6-bit relative PID will be enough;
         however, the X bit can be used to refer to older frames.

      X: 1 if this layer index has an extended P_DIFF.

      N: 1 if there is additional P_DIFF following the current P_DIFF.

4.2.1.  Scalability Structure (SS):

   The scalability structure (SS) data describes the resolution of each
   layer frame within a super frame as well as the inter-picture
   dependencies for a group of frames (GOF).  If the VP9 payload
   descriptor's "V" bit is set, the SS data is present in the position
   indicated in Figure 2 and Figure 3.









Uberti, et al.         Expires September 10, 2015              [Page 10]


Internet-Draft         RTP Payload Format for VP9             March 2015


        +-+-+-+-+-+-+-+-+
   V:   | N_S |Y|  N_G  |
        +-+-+-+-+-+-+-+-+              -\
   Y:   |     WIDTH     | (OPTIONAL)    .
        +               +               .
        |               | (OPTIONAL)    .
        +-+-+-+-+-+-+-+-+               . - N_S + 1 times
        |     HEIGHT    | (OPTIONAL)    .
        +               +               .
        |               | (OPTIONAL)    .
        +-+-+-+-+-+-+-+-+              -/            -\
   N_G: |  T  |U| R |-|-| (OPTIONAL)                 .
        +-+-+-+-+-+-+-+-+              -\            . - N_G + 1 times
        |    P_DIFF     | (OPTIONAL)    . - R times  .
        +-+-+-+-+-+-+-+-+              -/            -/

                                 Figure 4

   N_S:  N_S + 1 indicates the number of spatial layers present in the
      VP9 stream.

   Y: Each spatial layer's frame resolution present.  When set to one,
      the OPTIONAL WIDTH (2 octets) and HEIGHT (2 octets) MUST be
      present for each layer frame.  Otherwise, the resolution MUST NOT
      be present.

   N_G:  N_G + 1 indicates the number of frames in a GOF.  If N_G is
      greater than 0, then the SS data allows the inter-picture
      dependency structure of the VP9 stream to be pre-declared, rather
      than indicating it on the fly with every packet.  If N_G is
      greater than 0, then for N_G + 1 pictures in the GOF, each frame's
      temporal layer ID (T), switch up point (U), and the R reference
      indices (P_DIFFs) are specified.

      N_G=0 indicates that either there is only one temporal layer or no
      fixed inter-picture dependency information is present going
      forward in the bitstream.

      Note that for a given super frame, all layer frames follow the
      same inter-picture dependency structure.  However, the frame rate
      of each spatial layer can be different from each other and this
      can be controlled with the use of the D bit described above.  The
      specified dependency structure in the SS data MUST be for the
      highest frame rate layer.

   In a scalable stream sent with a fixed pattern, the SS data SHOULD be
   included in the first packet of every key frame.  This is a packet
   with P bit equal to zero, S or D bit equal to zero, B bit equal to 1,



Uberti, et al.         Expires September 10, 2015              [Page 11]


Internet-Draft         RTP Payload Format for VP9             March 2015


   and temporal layer ID (TID) equal to 0.  The SS data SHOULD also be
   included in the first packet of the first frame in which the SS
   changes.  If the SS data is included in a frame with TID not equal to
   0, it MUST also be repeated in the first packet of the first frame
   with a lower TID, until TID equals to 0.

4.3.  VP9 Payload Header

   TODO: need to describe VP9 payload header.

4.4.  Frame Fragmentation

   VP9 frames are fragmented into packets, in RTP sequence number order,
   beginning with a packet with the B bit set, and ending with a packet
   with the RTP marker bit set.  There is no mechanism for finer-grained
   access to parts of a VP9 frame.

4.5.  Examples of VP9 RTP Stream

   TODO

5.  Using VP9 with RPSI and SLI Feedback

   The VP9 payload descriptor defined in Section 4.2 above contains an
   optional PictureID parameter.  One use of this parameter is included
   to enable use of reference picture selection index (RPSI) and slice
   loss indication (SLI), both defined in [RFC4585].

5.1.  RPSI

   TODO: Update to indicate which frame within the picture.

   The reference picture selection index is a payload-specific feedback
   message defined within the RTCP-based feedback format.  The RPSI
   message is generated by a receiver and can be used in two ways.
   Either it can signal a preferred reference picture when a loss has
   been detected by the decoder -- preferably then a reference that the
   decoder knows is perfect -- or, it can be used as positive feedback
   information to acknowledge correct decoding of certain reference
   pictures.  The positive feedback method is useful for VP9 used as
   unicast.  The use of RPSI for VP9 is preferably combined with a
   special update pattern of the codec's two special reference frames --
   the golden frame and the altref frame -- in which they are updated in
   an alternating leapfrog fashion.  When a receiver has received and
   correctly decoded a golden or altref frame, and that frame had a
   PictureID in the payload descriptor, the receiver can acknowledge
   this simply by sending an RPSI message back to the sender.  The




Uberti, et al.         Expires September 10, 2015              [Page 12]


Internet-Draft         RTP Payload Format for VP9             March 2015


   message body (i.e., the "native RPSI bit string" in [RFC4585]) is
   simply the PictureID of the received frame.

5.2.  SLI

   TODO: Update to indicate which frame within the picture.

   The slice loss indication is another payload-specific feedback
   message defined within the RTCP-based feedback format.  The SLI
   message is generated by the receiver when a loss or corruption is
   detected in a frame.  The format of the SLI message is as follows
   [RFC4585]:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |         First           |        Number           | PictureID |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 5

   Here, First is the macroblock address (in scan order) of the first
   lost block and Number is the number of lost blocks.  PictureID is the
   six least significant bits of the codec-specific picture identifier
   in which the loss or corruption has occurred.  For VP9, this codec-
   specific identifier is naturally the PictureID of the current frame,
   as read from the payload descriptor.  If the payload descriptor of
   the current frame does not have a PictureID, the receiver MAY send
   the last received PictureID+1 in the SLI message.  The receiver MAY
   set the First parameter to 0, and the Number parameter to the total
   number of macroblocks per frame, even though only parts of the frame
   is corrupted.  When the sender receives an SLI message, it can make
   use of the knowledge from the latest received RPSI message.  Knowing
   that the last golden or altref frame was successfully received, it
   can encode the next frame with reference to that established
   reference.

5.3.  Example

   TODO: this example is copied from the VP8 payload format
   specification, and has not been updated for VP9.  It may be
   incorrect.

   The use of RPSI and SLI is best illustrated in an example.  In this
   example, the encoder may not update the altref frame until the last
   sent golden frame has been acknowledged with an RPSI message.  If an
   update is not received within some time, a new golden frame update is




Uberti, et al.         Expires September 10, 2015              [Page 13]


Internet-Draft         RTP Payload Format for VP9             March 2015


   sent instead.  Once the new golden frame is established and
   acknowledged, the same rule applies when updating the altref frame.

   +-------+-------------------+-------------------------+-------------+
   | Event | Sender            | Receiver                | Established |
   |       |                   |                         | reference   |
   +-------+-------------------+-------------------------+-------------+
   | 1000  | Send golden frame |                         |             |
   |       | PictureID = 0     |                         |             |
   |       |                   |                         |             |
   |       |                   | Receive and decode      |             |
   |       |                   | golden frame            |             |
   |       |                   |                         |             |
   | 1001  |                   | Send RPSI(0)            |             |
   |       |                   |                         |             |
   | 1002  | Receive RPSI(0)   |                         | golden      |
   |       |                   |                         |             |
   | ...   | (sending regular  |                         |             |
   |       | frames)           |                         |             |
   |       |                   |                         |             |
   | 1100  | Send altref frame |                         |             |
   |       | PictureID = 100   |                         |             |
   |       |                   |                         |             |
   |       |                   | Altref corrupted or     | golden      |
   |       |                   | lost                    |             |
   |       |                   |                         |             |
   | 1101  |                   | Send SLI(100)           | golden      |
   |       |                   |                         |             |
   | 1102  | Receive SLI(100)  |                         |             |
   |       |                   |                         |             |
   | 1103  | Send frame with   |                         |             |
   |       | reference to      |                         |             |
   |       | golden            |                         |             |
   |       |                   |                         |             |
   |       |                   | Receive and decode      | golden      |
   |       |                   | frame (decoder state    |             |
   |       |                   | restored)               |             |
   |       |                   |                         |             |
   | ...   | (sending regular  |                         |             |
   |       | frames)           |                         |             |
   |       |                   |                         |             |
   | 1200  | Send altref frame |                         |             |
   |       | PictureID = 200   |                         |             |
   |       |                   |                         |             |
   |       |                   | Receive and decode      | golden      |
   |       |                   | altref frame            |             |
   |       |                   |                         |             |
   | 1201  |                   | Send RPSI(200)          |             |



Uberti, et al.         Expires September 10, 2015              [Page 14]


Internet-Draft         RTP Payload Format for VP9             March 2015


   |       |                   |                         |             |
   | 1202  | Receive RPSI(200) |                         | altref      |
   |       |                   |                         |             |
   | ...   | (sending regular  |                         |             |
   |       | frames)           |                         |             |
   |       |                   |                         |             |
   | 1300  | Send golden frame |                         |             |
   |       | PictureID = 300   |                         |             |
   |       |                   |                         |             |
   |       |                   | Receive and decode      | altref      |
   |       |                   | golden frame            |             |
   |       |                   |                         |             |
   | 1301  |                   | Send RPSI(300)          | altref      |
   |       |                   |                         |             |
   | 1302  | RPSI lost         |                         |             |
   |       |                   |                         |             |
   | 1400  | Send golden frame |                         |             |
   |       | PictureID = 400   |                         |             |
   |       |                   |                         |             |
   |       |                   | Receive and decode      | altref      |
   |       |                   | golden frame            |             |
   |       |                   |                         |             |
   | 1401  |                   | Send RPSI(400)          |             |
   |       |                   |                         |             |
   | 1402  | Receive RPSI(400) |                         | golden      |
   +-------+-------------------+-------------------------+-------------+

          Table 1: Example signaling between sender and receiver

   Note that the scheme is robust to loss of the feedback messages.  If
   the RPSI is lost, the sender will try to update the golden (or
   altref) again after a while, without releasing the established
   reference.  Also, if an SLI is lost, the receiver can keep sending
   SLI messages at any interval allowed by the RTCP sending timing
   restrictions as specified in [RFC4585], as long as the picture is
   corrupted.

6.  Payload Format Parameters

   This payload format has two required parameters.

6.1.  Media Type Definition

   This registration is done using the template defined in [RFC6838] and
   following [RFC4855].

   Type name:  video




Uberti, et al.         Expires September 10, 2015              [Page 15]


Internet-Draft         RTP Payload Format for VP9             March 2015


   Subtype name:  VP9

   Required parameters:
      These parameters MUST be used to signal the capabilities of a
      receiver implementation.  These parameters MUST NOT be used for
      any other purpose.

      max-fr:  The value of max-fr is an integer indicating the maximum
         frame rate in units of frames per second that the decoder is
         capable of decoding.

      max-fs:  The value of max-fs is an integer indicating the maximum
         frame size in units of macroblocks that the decoder is capable
         of decoding.

         The decoder is capable of decoding this frame size as long as
         the width and height of the frame in macroblocks are less than
         int(sqrt(max-fs * 8)) - for instance, a max-fs of 1200 (capable
         of supporting 640x480 resolution) will support widths and
         heights up to 1552 pixels (97 macroblocks).

   Optional parameters:  none

   Encoding considerations:
      This media type is framed in RTP and contains binary data; see
      Section 4.8 of [RFC6838].

   Security considerations:  See Section 7 of RFC xxxx.
      [RFC Editor: Upon publication as an RFC, please replace "XXXX"
      with the number assigned to this document and remove this note.]

   Interoperability considerations:  None.

   Published specification:  VP9 bitstream format
      [I-D.grange-vp9-bitstream] and RFC XXXX.
      [RFC Editor: Upon publication as an RFC, please replace "XXXX"
      with the number assigned to this document and remove this note.]

   Applications which use this media type:
      For example: Video over IP, video conferencing.

   Additional information:  None.

   Person & email address to contact for further information:
      TODO [Pick a contact]

   Intended usage:  COMMON




Uberti, et al.         Expires September 10, 2015              [Page 16]


Internet-Draft         RTP Payload Format for VP9             March 2015


   Restrictions on usage:
      This media type depends on RTP framing, and hence is only defined
      for transfer via RTP [RFC3550].

   Author:  TODO [Pick a contact]

   Change controller:
      IETF Payload Working Group delegated from the IESG.

6.2.  SDP Parameters

   The receiver MUST ignore any fmtp parameter unspecified in this memo.

6.2.1.  Mapping of Media Subtype Parameters to SDP

   The media type video/VP9 string is mapped to fields in the Session
   Description Protocol (SDP) [RFC4566] as follows:

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

   o  The encoding name in the "a=rtpmap" line of SDP MUST be VP9 (the
      media subtype).

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

   o  The parameters "max-fs", and "max-fr", MUST be included in the
      "a=fmtp" line of SDP.  These parameters are expressed as a media
      subtype string, in the form of a semicolon separated list of
      parameter=value pairs.

6.2.1.1.  Example

   An example of media representation in SDP is as follows:

   m=video 49170 RTP/AVPF 98
   a=rtpmap:98 VP9/90000
   a=fmtp:98 max-fr=30; max-fs=3600;

6.2.2.  Offer/Answer Considerations

   TODO: Update this for VP9

7.  Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [RFC3550], and in any applicable RTP profile.  The main
   security considerations for the RTP packet carrying the RTP payload



Uberti, et al.         Expires September 10, 2015              [Page 17]


Internet-Draft         RTP Payload Format for VP9             March 2015


   format defined within this memo are confidentiality, integrity and
   source authenticity.  Confidentiality is achieved by encryption of
   the RTP payload.  Integrity of the RTP packets through suitable
   cryptographic integrity protection mechanism.  Cryptographic system
   may also allow the authentication of the source of the payload.  A
   suitable security mechanism for this RTP payload format should
   provide confidentiality, integrity protection and at least source
   authentication capable of determining if an RTP packet is from a
   member of the RTP session or not.  Note that the appropriate
   mechanism to provide security to RTP and payloads following this memo
   may vary.  It is dependent on the application, the transport, and the
   signaling protocol employed.  Therefore a single mechanism is not
   sufficient, although if suitable the usage of SRTP [RFC3711] is
   recommended.  This RTP payload format and its media decoder do not
   exhibit any significant non-uniformity in the receiver-side
   computational complexity for packet processing, and thus are unlikely
   to pose a denial-of-service threat due to the receipt of pathological
   data.  Nor does the RTP payload format contain any active content.

8.  Congestion Control

   Congestion control for RTP SHALL be used in accordance with RFC 3550
   [RFC3550], and with any applicable RTP profile; e.g., RFC 3551
   [RFC3551].  The congestion control mechanism can, in a real-time
   encoding scenario, adapt the transmission rate by instructing the
   encoder to encode at a certain target rate.  Media aware network
   elements MAY use the information in the VP9 payload descriptor in
   Section 4.2 to identify non-reference frames and discard them in
   order to reduce network congestion.  Note that discarding of non-
   reference frames cannot be done if the stream is encrypted (because
   the non-reference marker is encrypted).

9.  IANA Considerations

   The IANA is requested to register the following values:
   - Media type registration as described in Section 6.1.

10.  References

   [I-D.grange-vp9-bitstream]
              Grange, A. and H. Alvestrand, "A VP9 Bitstream Overview",
              draft-grange-vp9-bitstream-00 (work in progress), February
              2013.

   [I-D.lennox-avtext-lrr]
              Lennox, J., Uberti, J., Holmer, S., and M. Flodman, "The
              Layer Refresh Request (LRR) RTCP Feedback MessageVideo",
              draft-lennox-avtext-lrr-00 (work in progress), March 2015.



Uberti, et al.         Expires September 10, 2015              [Page 18]


Internet-Draft         RTP Payload Format for VP9             March 2015


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

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

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              July 2003.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

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

   [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, July
              2006.

   [RFC4855]  Casner, S., "Media Type Registration of RTP Payload
              Formats", RFC 4855, February 2007.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13, RFC
              6838, January 2013.

Authors' Addresses

   Justin Uberti
   Google, Inc.
   747 6th Street South
   Kirkland, WA  98033
   USA

   Email: justin@uberti.name


   Stefan Holmer
   Google, Inc.
   Kungsbron 2
   Stockholm  111 22
   Sweden





Uberti, et al.         Expires September 10, 2015              [Page 19]


Internet-Draft         RTP Payload Format for VP9             March 2015


   Magnus Flodman
   Google, Inc.
   Kungsbron 2
   Stockholm  111 22
   Sweden


   Jonathan Lennox
   Vidyo, Inc.
   433 Hackensack Avenue
   Seventh Floor
   Hackensack, NJ  07601
   US

   Email: jonathan@vidyo.com


   Danny Hong
   Vidyo, Inc.
   433 Hackensack Avenue
   Seventh Floor
   Hackensack, NJ  07601
   US

   Email: danny@vidyo.com


























Uberti, et al.         Expires September 10, 2015              [Page 20]


Html markup produced by rfcmarkup 1.124, available from https://tools.ietf.org/tools/rfcmarkup/