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Versions: (draft-westin-payload-vp8) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 RFC 7741

Payload Working Group                                          P. Westin
Internet-Draft                                                 H. Lundin
Intended status: Standards Track                               M. Glover
Expires: January 9, 2012                                       J. Uberti
                                                             F. Galligan
                                                                  Google
                                                            July 8, 2011


                    RTP Payload Format for VP8 Video
                       draft-ietf-payload-vp8-01

Abstract

   This memo describes an RTP payload format for the VP8 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.

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 January 9, 2012.

Copyright Notice

   Copyright (c) 2011 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
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions, Definitions and Acronyms  . . . . . . . . . . . .  4
   3.  Media Format Background  . . . . . . . . . . . . . . . . . . .  5
   4.  Payload Format . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  VP8 Payload Descriptor . . . . . . . . . . . . . . . . . .  7
     4.2.  VP8 Payload Header . . . . . . . . . . . . . . . . . . . .  9
     4.3.  Aggregated and Fragmented Payloads . . . . . . . . . . . . 10
     4.4.  Examples of VP8 RTP Stream . . . . . . . . . . . . . . . . 12
       4.4.1.  Key frame in a single RTP packet . . . . . . . . . . . 12
       4.4.2.  VP8 interframe in a single RTP packet; no PictureID  . 12
       4.4.3.  VP8 partitions in separate RTP packets . . . . . . . . 13
       4.4.4.  VP8 frame fragmented across RTP packets  . . . . . . . 14
       4.4.5.  VP8 frame with long PictureID  . . . . . . . . . . . . 16
   5.  Using VP8 with RPSI and SLI Feedback . . . . . . . . . . . . . 17
     5.1.  RPSI . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     5.2.  SLI  . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     5.3.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . 18
   6.  Payload Format Parameters  . . . . . . . . . . . . . . . . . . 21
     6.1.  Restrictions on usage  . . . . . . . . . . . . . . . . . . 21
     6.2.  Media Type Registration  . . . . . . . . . . . . . . . . . 21
     6.3.  SDP Parameters . . . . . . . . . . . . . . . . . . . . . . 22
       6.3.1.  Mapping of MIME Parameters to SDP  . . . . . . . . . . 22
     6.4.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . 22
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   8.  Congestion Control . . . . . . . . . . . . . . . . . . . . . . 24
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 25
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27

















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1.  Introduction

   This memo describes an RTP payload specification applicable to the
   transmission of video streams encoded using the VP8 video codec
   [I-D.bankoski-vp8-bitstream].  The format described in this document
   can be used both in peer-to-peer and video conferencing applications.

   The VP8 codec uses three different reference frames for interframe
   prediction: the previous frame, the golden frame, and the altref
   frame.  The payload specification in this memo has elements that
   enable advanced use of the reference frames, e.g., for improved loss
   robustness.

   One specific use case of the three reference frame types is temporal
   scalability.  By setting up the reference hierarchy in the
   appropriate way, up to five temporal layers can be encoded.  (How to
   set up the reference hierarchy for temporal scalability is not within
   the scope of this memo.)

   Another property of the VP8 codec is that it applies data
   partitioning to the encoded data.  Thus, an encoded VP8 frame can be
   divided into two or more partitions, as described in "VP8 Data Format
   and Decoding Guide" [I-D.bankoski-vp8-bitstream].  The first
   partition (prediction or mode) contains prediction mode parameters
   and motion vectors for all macroblocks.  The remaining partitions all
   contain the transform coefficients for the residuals.  The first
   partition is decodable without the remaining residual partitions.
   The subsequent partitions may be useful even if some part of the
   frame is lost.  This memo allows the partitions to be sent separately
   or in the same RTP packet.  It may be beneficial for decoder error-
   concealment to send the partitions in different packets, even though
   it is not mandatory according to this specification.

   The format specification is described in Section 4.  In Section 5, a
   method to acknowledge receipt of reference frames using RTCP
   techniques is described.

   The payload partitioning and the acknowledging method both serve as
   motivation for three of the fields included in the payload format:
   the "PartID", "1st partition size" and "PictureID" fields.  The
   ability to encode a temporally scalable stream motivates the
   "TL0PICIDX" and "TID" fields.









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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].














































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3.  Media Format Background

   VP8 is based on decomposition of frames into square sub-blocks of
   pixels, prediction of such sub-blocks using previously constructed
   blocks, and adjustment of such predictions (as well as synthesis of
   unpredicted blocks) using a discrete cosine transform (hereafter
   abbreviated as DCT).  In one special case, however, VP8 uses a
   "Walsh-Hadamard" (hereafter abbreviated as WHT) transform instead of
   a DCT.  An encoded VP8 frame is divided into two or more partitions,
   as described in [I-D.bankoski-vp8-bitstream].  The first partition
   (prediction or mode) contains prediction mode parameters and motion
   vectors for all macroblocks.  The remaining partitions all contain
   the quantized DCT/WHT coefficients for the residuals.  There can be
   1, 2, 4, or 8 DCT/WHT partitions per frame, depending on encoder
   settings.




































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4.  Payload Format

   The general RTP payload format for VP8 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             |
     |                             ....                              |
     +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
     |            VP8 payload descriptor (integer #bytes)            |
     :                                                               :
     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               : VP8 payload header (3 octets) |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | VP8 pyld hdr  :                                               |
     +-+-+-+-+-+-+-+-+                                               |
     :                   Bytes 4..N of VP8 payload                   :
     |                                                               |
     |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               :    OPTIONAL RTP padding       |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The VP8 payload descriptor and VP8 payload header will be described
   in the sequel.  OPTIONAL RTP padding MUST NOT be included unless the
   P bit is set.

                                 Figure 1

   Marker bit:  The marker bit indicates the last packet part of a
      frame.  This enables a decoder to finish decoding the picture,
      where it otherwise may need to wait for the next packet to
      explicitly know that the frame is complete.

   Timestamp:  The RTP timestamp indicates the time when the frame was
      sampled at a clock rate of 90 kHz.

   Sequence number:  The sequence numbers are monotonically increasing
      and set as packets are sent.






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

4.1.  VP8 Payload Descriptor

   The first octets after the RTP header are the VP8 payload descriptor,
   with the following structure.

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |X|R|N|S|PartID | (REQUIRED)
      +-+-+-+-+-+-+-+-+
   X: |I|L|T|  RSV-A  | (OPTIONAL)
      +-+-+-+-+-+-+-+-+
   I: |   PictureID   | (OPTIONAL)
      +-+-+-+-+-+-+-+-+
   L: |   TL0PICIDX   | (OPTIONAL)
      +-+-+-+-+-+-+-+-+
   T: | TID |  RSV-B  | (OPTIONAL)
      +-+-+-+-+-+-+-+-+

                                 Figure 2

   X: Extended control bits present.  When set to one, the extension
      octet MUST be provided immediately after the mandatory first
      octet.  If the bit is zero, all optional fields MUST be omitted.

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

   N: Non-reference frame.  When set to one, the frame can be discarded
      without affecting any other future or past frames.  If the
      reference status of the frame is unknown, this bit SHOULD be set
      to zero to avoid discarding frames needed for reference.

         Informative note: This document does not describe how to
         determine if an encoded frame is non-reference.  The reference
         status of an encoded frame is preferably provided from the
         encoder implementation.

   S: Start of VP8 partition.  SHOULD be set to 1 when the first payload
      octet of the RTP packet is the beginning of a new VP8 partition,
      and MUST NOT be 1 otherwise.  The S bit MUST be set to 1 for the
      first packet of each encoded frame.







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   PartID:  Partition index.  Denotes which VP8 partition the first
      payload octet of the packet belongs to.  The first VP8 partition
      (containing modes and motion vectors) MUST be labeled with PartID
      = 0.  PartID SHOULD be incremented for each subsequent partition,
      but MAY be kept at 0 for all packets.  PartID MUST NOT be larger
      than 8.  If more than one packet in an encoded frame contains the
      same PartID, the S bit MUST NOT be set for any other packet than
      the first packet with that PartID.

   When the X bit is set to 1 in the first octet, the OPTIONAL extension
   bit field MUST be present in the second octet.  If the X bit is 0,
   the extension bit field MUST NOT be present, and all bits below MUST
   be implicitly interpreted as 0.

   I: PictureID present.  When set to one, the OPTIONAL PictureID MUST
      be present after the extension bit field and specified as below.
      Otherwise, PictureID MUST NOT be present.

   L: TL0PICIDX present.  When set to one, the OPTIONAL TL0PICIDX MUST
      be present and specified as below, and the T bit MUST be set to 1.
      Otherwise, TL0PICIDX MUST NOT be present.

   T: TID present.  When set to one, the OPTIONAL TID field MUST be
      present and specified as below, and the RSV-B field MUST be
      present and set to zero.  Otherwise, TID and RSV-B MUST NOT be
      present.

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

   After the extension bit field follow the extension data fields that
   are enabled.

   PictureID:  8 or 16 bits.  This is a running index of the frames.
      The field MUST be present if the I bit is equal to one.  The most
      significant bit of the first octet is an extension flag.  The 7
      following bits carry (parts of) the PictureID.  If the extension
      flag is one, the PictureID continues in the next octet forming a
      15 bit index, where the 8 bits in the second octet are the least
      significant bits of the PictureID.  If the extension flag is zero,
      there is no extension, and the PictureID is the 7 remaining bits
      of the first (and only) octet.  The sender may choose 7 or 15 bits
      index.  The PictureID SHOULD start on a random number, and MUST
      wrap after reaching the maximum ID.







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   TL0PICIDX:  8 bits temporal level zero index.  The field MUST be
      present if the L bit is equal to 1, and MUST NOT be present
      otherwise.  TL0PICIDX is a running index for the temporal base
      layer frames, i.e., the frames with TID set to 0.  If TID is
      larger than 0, TL0PICIDX indicates which base layer frame the
      current image 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.

   TID:  3 bits temporal layer index.  The field MUST be present when
      the T bit is equal to 1, and MUST NOT be present otherwise.  The
      TID field indicates which temporal layer the packet represents.
      The lowest layer, i.e., the base layer, MUST have TID set to 0.
      Higher layers SHOULD increment the TID according to their position
      in the layer hierarchy.

   RSV-B:  Bits reserved for future use.  MUST be present when the T bit
      is equal to 1, MUST be set to zero and MUST be ignored by the
      receiver.  If the T bit is equal to 0, the field MUST NOT be
      present.

4.2.  VP8 Payload Header

   The first three octets of an encoded VP8 frame are referred to as an
   "uncompressed data chunk" in [I-D.bankoski-vp8-bitstream], and co-
   serve as payload header in this RTP format.  The codec bitstream
   format specifies two different variants of the uncompressed data
   chunk: a 3 octet version for interframes and a 10 octet version for
   key frames.  The first 3 octets are common to both variants.  In the
   case of a key frame the remaining 7 octets are considered to be part
   of the remaining payload in this RTP format.  Note that the header is
   present only in packets which have the S bit equal to one and the
   PartID equal to zero in the payload descriptor.  Subsequent packets
   for the same frame do not carry the payload header.

















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      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |Size0|H| VER |P|
     +-+-+-+-+-+-+-+-+
     |     Size1     |
     +-+-+-+-+-+-+-+-+
     |     Size2     |
     +-+-+-+-+-+-+-+-+
     | Bytes 4..N of |
     | VP8 payload   |
     :               :
     +-+-+-+-+-+-+-+-+
     | OPTIONAL RTP  |
     | padding       |
     :               :
     +-+-+-+-+-+-+-+-+

                                 Figure 3

   H: Show frame bit as defined in [I-D.bankoski-vp8-bitstream].

   VER:  A version number as defined in [I-D.bankoski-vp8-bitstream].

   P: Inverse key frame flag.  When set to 0 the current frame is a key
      frame.  When set to 1 the current frame is an interframe.  Defined
      in [I-D.bankoski-vp8-bitstream]

   SizeN:  The size of the first partition size in bytes is calculated
      from the 19 bits in Size0, Size1, and Size2 as 1stPartitionSize =
      Size0 + 8 * Size1 + 2048 * Size2.  [I-D.bankoski-vp8-bitstream].

4.3.  Aggregated and Fragmented Payloads

   An encoded VP8 frame can be divided into two or more partitions, as
   described in Section 3.  One packet can contain a fragment of a
   partition, a complete partition, or an aggregate of fragments and
   partitions.  In the preferred use case, the S bit and PartID fields
   described in Section 4.1 should be used to indicate what the packet
   contains.  The PartID field should indicate which partition the first
   octet of the payload belongs to, and the S bit indicates that the
   packet starts on a new partition.  Aggregation of encoded partitions
   is done without explicit signaling.  Partitions MUST be aggregated in
   decoding order.  Two fragments from different partitions MAY be
   aggregated into the same packet.  An aggregation MUST have exactly
   one payload descriptor.  Aggregated partitions MUST represent parts
   of one and the same video frame.  Consequently, an aggregated packet
   will have one or no payload header, depending on whether the
   aggregate contains the beginning of the first partition of a frame or



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   not, respectively.  Note that the length of the first partition can
   always be obtained from the first partition size parameter in the VP8
   payload header.

   The VP8 bitstream format [I-D.bankoski-vp8-bitstream] specifies that
   if multiple DCT/WHT partitions are produced, the location of each
   partition start is found at the end of the first (prediction/mode)
   partition.  In this RTP payload specification, the location offsets
   are considered to be part of the first partition.

   It is OPTIONAL for a packetizer implementing this RTP specification
   to pay attention to the partition boundaries within an encoded frame.
   If packetization of a frame is done without considering the partition
   boundaries, the PartID field MAY be set to zero for all packets, and
   the S bit MUST NOT be set to one for any other packet than the first.




































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4.4.  Examples of VP8 RTP Stream

   A few examples of how the VP8 RTP payload can be used are included
   below.

4.4.1.  Key frame in a single RTP packet

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 1        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|1|0 0 0 0| X = 1; S = 1; PartID = 0
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1
     +-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 0 1| PictureID = 17
     +-+-+-+-+-+-+-+-+
     |Size0|1| VER |0| P = 0
     +-+-+-+-+-+-+-+-+
     |     Size1     |
     +-+-+-+-+-+-+-+-+
     |     Size2     |
     +-+-+-+-+-+-+-+-+
     | VP8 payload   |
     +-+-+-+-+-+-+-+-+

4.4.2.  VP8 interframe in a single RTP packet; no PictureID

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 1        |
     +-+-+-+-+-+-+-+-+
     |0|0|0|1|0 0 0 0| X = 0; S = 1; PartID = 0
     +-+-+-+-+-+-+-+-+
     |Size0|1| VER |1| P = 1
     +-+-+-+-+-+-+-+-+
     |     Size1     |
     +-+-+-+-+-+-+-+-+
     |     Size2     |
     +-+-+-+-+-+-+-+-+
     | VP8 payload   |
     +-+-+-+-+-+-+-+-+







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4.4.3.  VP8 partitions in separate RTP packets

   First RTP packet; complete first partition.

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 0        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|1|0 0 0 0| X = 1; S = 1; PartID = 0
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1
     +-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 0 1| PictureID = 17
     +-+-+-+-+-+-+-+-+
     |Size0|1| VER |1| P = 1
     +-+-+-+-+-+-+-+-+
     |     Size1     |
     +-+-+-+-+-+-+-+-+
     |     Size2     |
     +-+-+-+-+-+-+-+-+
     | Bytes 4..L of |
     | first VP8     |
     | partition     |
     :               :
     +-+-+-+-+-+-+-+-+

   Second RTP packet; complete second partition.

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 1        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|1|0 0 0 1| X = 1; S = 1; PartID = 1
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1
     +-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 0 1| PictureID = 17
     +-+-+-+-+-+-+-+-+
     | Remaining VP8 |
     | partitions    |
     :               :
     +-+-+-+-+-+-+-+-+







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4.4.4.  VP8 frame fragmented across RTP packets

   First RTP packet; complete first partition.

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 0        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|1|0 0 0 0| X = 1; S = 1; PartID = 0
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1
     +-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 0 1| PictureID = 17
     +-+-+-+-+-+-+-+-+
     |Size0|1| VER |1| P = 1
     +-+-+-+-+-+-+-+-+
     |     Size1     |
     +-+-+-+-+-+-+-+-+
     |     Size2     |
     +-+-+-+-+-+-+-+-+
     | Complete      |
     | first         |
     | partition     |
     :               :
     +-+-+-+-+-+-+-+-+

   Second RTP packet; first fragment of second partition.

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 0        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|1|0 0 0 1| X = 1; S = 1; PartID = 1
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1
     +-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 0 1| PictureID = 17
     +-+-+-+-+-+-+-+-+
     | First fragment|
     | of second     |
     | partition     |
     :               :
     +-+-+-+-+-+-+-+-+






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   Third RTP packet; second fragment of second partition.

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 0        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|0|0 0 0 1| X = 1; S = 0; PartID = 1
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1
     +-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 0 1| PictureID = 17
     +-+-+-+-+-+-+-+-+
     | Mid fragment  |
     | of second     |
     | partition     |
     :               :
     +-+-+-+-+-+-+-+-+

   Fourth RTP packet; last fragment of second partition.

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 1        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|0|0 0 0 1| X = 1; S = 0; PartID = 1
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1
     +-+-+-+-+-+-+-+-+
     |0 0 0 0 1 0 0 1| PictureID = 17
     +-+-+-+-+-+-+-+-+
     | Last fragment |
     | of second     |
     | partition     |
     :               :
     +-+-+-+-+-+-+-+-+














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4.4.5.  VP8 frame with long PictureID

   PictureID = 4711 = 001001001100111 binary (first 7 bits: 0010010,
   last 8 bits: 01100111).

      0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |  RTP header   |
     |  M = 1        |
     +-+-+-+-+-+-+-+-+
     |1|0|0|1|0 0 0 0| X = 1; S = 1; PartID = 0
     +-+-+-+-+-+-+-+-+
     |1|0|0|0 0 0 0 0| I = 1;
     +-+-+-+-+-+-+-+-+
     |1 0 0 1 0 0 1 0| Long PictureID flag = 1
     |0 1 1 0 0 1 1 1| PictureID = 4711
     +-+-+-+-+-+-+-+-+
     |Size0|1| VER |1|
     +-+-+-+-+-+-+-+-+
     |     Size1     |
     +-+-+-+-+-+-+-+-+
     |     Size2     |
     +-+-+-+-+-+-+-+-+
     | Bytes 4..N of |
     | VP8 payload   |
     :               :
     +-+-+-+-+-+-+-+-+
























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5.  Using VP8 with RPSI and SLI Feedback

   The VP8 payload descriptor defined in Section 4.1 above contains an
   optional PictureID parameter.  This parameter is included mainly to
   enable use of reference picture selection index (RPSI) and slice loss
   indication (SLI), both defined in [RFC4585].

5.1.  RPSI

   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 VP8 used as
   unicast.  The use of RPSI for VP8 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
   message body (i.e., the "native RPSI bit string" in [RFC4585]) is
   simply the PictureID of the received frame.

5.2.  SLI

   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 4

   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 VP8, this codec-
   specific identifier is naturally the PictureID of the current frame,



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   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

   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
   sent instead.  Once the new golden frame is established and
   acknowledge, 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)  |                         |             |
   |       |                   |                         |             |




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   | 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)          |             |
   |       |                   |                         |             |
   | 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: Exemple signaling between sender and receiver

   Note that the scheme is robust to loss of the feedback messages.  If



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   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, as long as the picture is corrupted.















































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6.  Payload Format Parameters

   This section specifies the parameters that MAY be used to select
   optional features of the payload format and certain features of the
   bitstream.

6.1.  Restrictions on usage

   This media type depends on RTP framing, and hence is only defined for
   transfer via RTP [RFC3550] [RFC3550].Transport within other framing
   protocols is not defined at this time.

6.2.  Media Type Registration

   This registration is done using the template defined in [RFC4288] and
   following [RFC4855].

   Type name:  video

   Subtype name:  VP8

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:
      This media type is framed and contains binary data; see Section
      4.8 of [RFC4288].

   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:  VP8 bitstream format
      [I-D.bankoski-vp8-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.







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   Person & email address to contact for further information:
      Patrik Westin, patrik.westin@gmail.com

   Intended usage:  COMMON

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

   Author:  Patrik Westin, patrik.westin@gmail.com

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

6.3.  SDP Parameters

   The receiver MUST ignore any parameter unspecified in this memo.

6.3.1.  Mapping of MIME Parameters to SDP

   The MIME media type video/VP8 string is mapped to fields in the
   Session Description Protocol (SDP) [RFC2327] 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 VP8 (the
      MIME subtype).

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

   o  The OPTIONAL parameter "version", if included, MUST be in the
      a=fmtp SDP field.  This parameter matches the VP8 bitstream
      version.

6.4.  Example

   An example of media representation in SDP is as follows:

   m=video 49170 RTP/AVPF 98
   a=rtpmap:98 VP8/90000
   a=fmtp:98 version=0










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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
   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.



























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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 VP8 payload descriptor in
   Section 4.1 to identify non-reference frames and discard them in
   order to reduce network congestion.









































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9.  IANA Considerations

   The IANA is requested to register the following values:
   - Media type registration as described in Section 6.2.















































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10.  References

   [I-D.bankoski-vp8-bitstream]
              Bankoski, J., Koleszar, J., Quillio, L., Salonen, J.,
              Wilkins, P., and Y. Xu, "VP8 Data Format and Decoding
              Guide", draft-bankoski-vp8-bitstream-04 (work in
              progress), June 2011.

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

   [RFC2327]  Handley, M. and V. Jacobson, "SDP: Session Description
              Protocol", RFC 2327, April 1998.

   [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.

   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [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.















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Authors' Addresses

   Patrik Westin
   Google, Inc.
   Kungsbron 2
   Stockholm,   11122
   Sweden

   Email: patrik.westin@gmail.com


   Henrik F Lundin
   Google, Inc.
   Kungsbron 2
   Stockholm,   11122
   Sweden

   Email: hlundin@google.com


   Michael Glover
   Google, Inc.


   Justin Uberti
   Google, Inc.


   Frank Galligan
   Google, Inc.





















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