One document matched: draft-ietf-payload-vp8-01.xml
<?xml version="1.0"?>
<!DOCTYPE rfc SYSTEM 'rfc2629.dtd' [
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<!ENTITY rfc2327 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2327.xml">
<!ENTITY vp8 SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.bankoski-vp8-bitstream.xml">
]>
<rfc
category="std"
docName="draft-ietf-payload-vp8-01"
ipr="trust200902">
<?rfc symrefs="yes" ?>
<?rfc sortrefs="yes" ?> <!-- alphabetize the references -->
<?rfc comments="no"?> <!-- show comments -->
<?rfc inline="yes" ?> <!-- comments are inline -->
<?rfc toc="yes" ?> <!-- generate table of contents -->
<front>
<title abbrev="RTP Payload Format for VP8">
RTP Payload Format for VP8 Video
</title>
<author initials="P." surname="Westin" fullname="Patrik Westin">
<organization abbrev="Google">
Google, Inc.
</organization>
<address>
<postal>
<street>Kungsbron 2</street>
<city>Stockholm</city>
<region></region>
<code>11122</code>
<country>Sweden</country>
</postal>
<email>patrik.westin@gmail.com</email>
</address>
</author>
<author initials="H.F." surname="Lundin"
fullname="Henrik F Lundin">
<organization abbrev="Google">
Google, Inc.
</organization>
<address>
<postal>
<street>Kungsbron 2</street>
<city>Stockholm</city>
<region></region>
<code>11122</code>
<country>Sweden</country>
</postal>
<email>hlundin@google.com</email>
</address>
</author>
<author initials="M." surname="Glover"
fullname="Michael Glover">
<organization abbrev="Google">
Google, Inc.
</organization>
</author>
<author initials="J." surname="Uberti"
fullname="Justin Uberti">
<organization abbrev="Google">
Google, Inc.
</organization>
</author>
<author initials="F." surname="Galligan"
fullname="Frank Galligan">
<organization abbrev="Google">
Google, Inc.
</organization>
</author>
<date month="July" year="2011" />
<area>General</area>
<workgroup>Payload Working Group</workgroup>
<keyword>RFC</keyword>
<keyword>Request for Comments</keyword>
<keyword>RTP</keyword>
<keyword>VP8</keyword>
<keyword>WebM</keyword>
<abstract>
<t> 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.</t></abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>
This memo describes an RTP payload specification applicable to the transmission of video
streams encoded using the VP8 video codec <xref target="I-D.bankoski-vp8-bitstream" />.
The format described in
this document can be used both in peer-to-peer and video conferencing applications.
</t><t>
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.
</t><t>
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.)
</t><t>
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" <xref target="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.
</t><t>
The format specification is described in
<xref target="payloadFormat" />. In <xref target="RPSIandSLI" />, a method
to acknowledge receipt of reference frames using RTCP techniques is described.
</t><t>
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.
</t>
</section>
<section anchor="conventions" title="Conventions, Definitions and Acronyms">
<t>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 <xref target="RFC2119"/>.</t>
</section>
<section anchor="mediaFormatBackground" title = "Media Format Background">
<t>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 <xref target="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.</t>
</section>
<section anchor="payloadFormat" title="Payload Format">
<figure anchor="figureRTPHeader">
<preamble>
The general RTP payload format for VP8 is depicted below.</preamble>
<artwork>
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
<postamble>
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.
</postamble>
</figure>
<t>
<list style="hanging">
<t hangText="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.</t>
<t hangText="Timestamp:">
The RTP timestamp indicates the time when the frame was sampled at a
clock rate of 90 kHz.</t>
<t hangText="Sequence number:">
The sequence numbers are monotonically increasing
and set as packets are sent.</t>
<t>
The remaining RTP header fields are used as specified in <xref target="RFC3550" />.
</t>
</list>
</t>
<section anchor="VP8payloadDescriptor" title = "VP8 Payload Descriptor">
<figure anchor="figureVP8payloadDescriptor">
<preamble>
The first octets after the RTP header are the VP8 payload descriptor, with the
following structure.</preamble>
<artwork>
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)
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
<list style="hanging">
<t hangText="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.</t>
<t hangText="R:">
Bit reserved for future use. MUST be set to zero and MUST be ignored by the
receiver.</t>
<t hangText="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.
<list style="empty">
<t> 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.
</t>
</list>
</t>
<t hangText="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.</t>
<t hangText="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.</t>
</list>
</t>
<t>
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.
<list style="hanging">
<t hangText="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.</t>
<t hangText="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>
<t hangText="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.
</t>
<t hangText="RSV-A:">
Bits reserved for future use. MUST be set to zero and MUST be ignored by the
receiver.</t>
</list>
</t>
<t>
After the extension bit field follow the extension data fields that are enabled.
<list style="hanging">
<t hangText="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.
</t>
<t hangText="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.
</t>
<t hangText="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.
</t>
<t hangText="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.
</t>
</list>
</t>
</section>
<section anchor="VP8payloadHeader" title = "VP8 Payload Header">
<t>
The first three octets of an encoded VP8 frame are referred to as an "uncompressed data
chunk" in <xref target="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.
</t>
<figure anchor="figureVP8payloadHeader">
<!--
<preamble>
The first three bytes of an encoded VP8 frame are referred to as an "uncompressed data
chunk" in <xref target="I-D.bankoski-vp8-bitstream" />, and co-serve as payload header in this RTP format. Note
that the header is present only in packets which have the B bit equal to one in the
payload descriptor. Subsequent packets for the same frame do not carry the payload
header.
</preamble>
-->
<artwork>
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|Size0|H| VER |P|
+-+-+-+-+-+-+-+-+
| Size1 |
+-+-+-+-+-+-+-+-+
| Size2 |
+-+-+-+-+-+-+-+-+
| Bytes 4..N of |
| VP8 payload |
: :
+-+-+-+-+-+-+-+-+
| OPTIONAL RTP |
| padding |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
<list style="hanging">
<t hangText="H:">Show frame bit as defined in <xref target="I-D.bankoski-vp8-bitstream" />.</t>
<t hangText="VER:">A version number as defined in <xref target="I-D.bankoski-vp8-bitstream" />.</t>
<t hangText="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 <xref target="I-D.bankoski-vp8-bitstream" /></t>
<t hangText="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.
<xref target="I-D.bankoski-vp8-bitstream" />.</t>
</list>
</t>
</section>
<section title = "Aggregated and Fragmented Payloads">
<t>
An encoded VP8 frame can be divided into two or more partitions, as described in
<xref target="mediaFormatBackground" />.
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 <xref target="VP8payloadDescriptor" />
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 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.
</t>
<t>
The VP8 bitstream format <xref target="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.
</t>
<t>
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.
</t>
<t><vspace blankLines="100" /></t> <!-- force a pagebreak-->
</section>
<section title = "Examples of VP8 RTP Stream">
<t>A few examples of how the VP8 RTP payload can be used are included below.</t>
<section title = "Key frame in a single RTP packet">
<figure>
<artwork>
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 |
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section title = "VP8 interframe in a single RTP packet; no PictureID">
<figure>
<artwork>
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 |
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t><vspace blankLines="100" /></t> <!-- force a pagebreak-->
</section>
<section title = "VP8 partitions in separate RTP packets">
<figure>
<preamble>
First RTP packet; complete first partition.
</preamble>
<artwork>
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 |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<figure>
<preamble>
Second RTP packet; complete second partition.
</preamble>
<artwork>
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 |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section title = "VP8 frame fragmented across RTP packets">
<figure>
<preamble>
First RTP packet; complete first partition.
</preamble>
<artwork>
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 |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<figure>
<preamble>
Second RTP packet; first fragment of second partition.
</preamble>
<artwork>
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 |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<figure>
<preamble>
Third RTP packet; second fragment of second partition.
</preamble>
<artwork>
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 |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<figure>
<preamble>
Fourth RTP packet; last fragment of second partition.
</preamble>
<artwork>
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 |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
<section title = "VP8 frame with long PictureID">
<figure>
<preamble>
PictureID = 4711 = 001001001100111 binary (first 7 bits: 0010010, last 8 bits: 01100111).
</preamble>
<artwork>
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 |
: :
+-+-+-+-+-+-+-+-+
</artwork>
</figure>
</section>
</section>
</section>
<section anchor="RPSIandSLI" title = "Using VP8 with RPSI and SLI Feedback">
<t>
The VP8 payload descriptor defined in <xref target="VP8payloadDescriptor" /> 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 <xref target="RFC4585" />.</t>
<section anchor="RPSI" title = "RPSI">
<t>
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 <xref target="RFC4585" />) is simply the PictureID of the
received frame.</t>
</section>
<section anchor="SLI" title = "SLI">
<t>
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
<xref target="RFC4585" />:</t>
<figure anchor="figureSLIHeader">
<artwork>
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>
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, 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.
</t>
</section>
<section title = "Example">
<t>
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.</t>
<texttable
anchor="table_example_timing"
title="Exemple signaling between sender and receiver">
<ttcol align='left'>Event</ttcol>
<ttcol align='left'>Sender</ttcol>
<ttcol align='left'>Receiver</ttcol>
<ttcol align='left'>Established reference</ttcol>
<c>1000</c> <c>Send golden frame PictureID = 0</c> <c></c> <c></c>
<c></c> <c></c> <c> Receive and decode golden frame </c> <c></c>
<c>1001</c> <c></c> <c>Send RPSI(0)</c> <c></c>
<c>1002</c> <c>Receive RPSI(0)</c> <c></c> <c>golden</c>
<c>...</c> <c>(sending regular frames)</c> <c></c> <c></c>
<c>1100</c> <c>Send altref frame PictureID = 100</c> <c></c> <c></c>
<c></c> <c></c> <c>Altref corrupted or lost</c> <c>golden</c>
<c>1101</c> <c></c> <c>Send SLI(100)</c> <c>golden</c>
<c>1102</c> <c>Receive SLI(100)</c> <c></c> <c></c>
<c>1103</c> <c>Send frame with reference to golden</c> <c></c> <c></c>
<c></c> <c></c> <c>Receive and decode frame (decoder state restored)</c> <c>golden</c>
<c>...</c> <c>(sending regular frames)</c> <c></c> <c></c>
<c>1200</c> <c>Send altref frame PictureID = 200</c> <c></c> <c></c>
<c></c> <c></c> <c>Receive and decode altref frame</c> <c>golden</c>
<c>1201</c> <c></c> <c>Send RPSI(200)</c> <c></c>
<c>1202</c> <c>Receive RPSI(200)</c> <c></c> <c>altref</c>
<c>...</c> <c>(sending regular frames)</c> <c></c> <c></c>
<c>1300</c> <c>Send golden frame PictureID = 300</c> <c></c> <c></c>
<c></c> <c></c> <c>Receive and decode golden frame</c> <c>altref</c>
<c>1301</c> <c></c> <c>Send RPSI(300)</c> <c>altref</c>
<c>1302</c> <c>RPSI lost</c> <c></c> <c></c>
<c>1400</c> <c>Send golden frame PictureID = 400</c> <c></c> <c></c>
<c></c> <c></c> <c>Receive and decode golden frame</c> <c>altref</c>
<c>1401</c> <c></c> <c>Send RPSI(400)</c> <c></c>
<c>1402</c> <c>Receive RPSI(400)</c> <c></c> <c>golden</c>
</texttable>
<t>
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, as long as the picture is corrupted.</t>
</section>
</section>
<section anchor="payloadFormatParameters" title = "Payload Format Parameters">
<t>
This section specifies the parameters that MAY be used to select optional features of
the payload format and certain features of the bitstream.</t>
<section anchor="restrictionsOnUsage" title = "Restrictions on usage">
<t>
This media type depends on RTP framing, and hence is only defined for transfer via RTP
[RFC3550] <xref target="RFC3550" />.Transport within other framing protocols is not defined at
this time.</t>
</section>
<section anchor="mediaTypeRegistration" title = "Media Type Registration">
<t>This registration is done using the template defined in <xref target="RFC4288"/>
and following <xref target="RFC4855"/>.
<list style="hanging">
<t hangText="Type name:">
video
</t>
<t hangText="Subtype name:">
VP8
</t>
<t hangText="Required parameters:">
none
</t>
<t hangText="Optional parameters:">
none
</t>
<t hangText="Encoding considerations:">
<vspace blankLines="0"/>
This media type is framed and contains binary data; see Section 4.8 of
<xref target="RFC4288"/>.
</t>
<t hangText="Security considerations:">
See <xref target="securityConsiderations" /> of RFC xxxx.
<vspace blankLines="0"/>
[RFC Editor: Upon publication as an RFC, please replace "XXXX" with the number assigned to this document
and remove this note.]
</t>
<t hangText="Interoperability considerations:">
None.
</t>
<t hangText="Published specification:">
VP8 bitstream format <xref target="I-D.bankoski-vp8-bitstream"/> and RFC XXXX.
<vspace blankLines="0"/>
[RFC Editor: Upon publication as an RFC, please replace "XXXX" with the number assigned to this document
and remove this note.]
<vspace blankLines="0"/>
</t>
<t hangText="Applications which use this media type:">
<vspace blankLines="0"/>
For example: Video over IP, video conferencing.
</t>
<t hangText="Additional information:">
None.
</t>
<t hangText="Person & email address to contact for further information:">
<vspace blankLines="0"/>
Patrik Westin, patrik.westin@gmail.com
</t>
<t hangText="Intended usage:">
COMMON
</t>
<t hangText="Restrictions on usage:">
<vspace blankLines="0"/>
This media type depends on RTP framing, and hence is only defined for transfer via RTP <xref target="RFC3550"/>.
</t>
<t hangText="Author:">
Patrik Westin, patrik.westin@gmail.com
</t>
<t hangText="Change controller:">
<vspace blankLines="0"/>
IETF Payload Working Group delegated from the IESG.
</t>
</list>
</t>
</section>
<section title = "SDP Parameters">
<t>The receiver MUST ignore any parameter unspecified in this memo.</t>
<section title = "Mapping of MIME Parameters to SDP">
<t>
The MIME media type video/VP8 string is mapped to fields in the Session Description
Protocol (SDP) <xref target="RFC2327" /> as follows:
<list style="symbols">
<t> The media name in the "m=" line of SDP MUST be video.</t>
<t>
The encoding name in the "a=rtpmap" line of SDP MUST be VP8 (the MIME
subtype).
</t>
<t> The clock rate in the "a=rtpmap" line MUST be 90000.</t>
<t>
The OPTIONAL parameter "version", if included, MUST be in the a=fmtp SDP field.
This parameter matches the VP8 bitstream version.
</t>
</list>
</t>
</section>
</section>
<section title = "Example">
<t> An example of media representation in SDP is as follows:</t>
<t>
m=video 49170 RTP/AVPF 98<vspace blankLines="0" />
a=rtpmap:98 VP8/90000<vspace blankLines="0" />
a=fmtp:98 version=0<vspace blankLines="0" />
</t>
</section>
</section>
<section anchor="securityConsiderations" title = "Security Considerations">
<t>
RTP packets using the payload format defined in this specification
are subject to the security considerations discussed in the RTP
specification <xref target="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 <xref target="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.
</t>
</section>
<section anchor="congestionControl" title = "Congestion Control">
<t>
Congestion control for RTP SHALL be used in accordance with RFC
3550 <xref target="RFC3550" />, and with any applicable RTP profile; e.g., RFC 3551
<xref target="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 <xref target="VP8payloadDescriptor" />
to identify non-reference frames and discard
them in order to reduce network congestion.
</t>
</section>
<section anchor="IANAConsiderations" title = "IANA Considerations">
<t>
The IANA is requested to register the following values:<vspace blankLines="0" />
- Media type registration as described in <xref target="mediaTypeRegistration" />.</t>
</section>
</middle>
<back>
<references>
<!--
<reference anchor="VP8" target="http://www.webmproject.org">
<front>
<title>VP8 Data Format and Decoding Guide</title>
<author surname="Google, Inc." fullname="WebM Project">
<organization abbrev="Google">Google, Inc.</organization></author>
<date month="July" year="2010" />
</front>
</reference>
-->
&vp8; <!-- I-D.bankoski-vp8-bitstream -->
&rfc2119;
&rfc4585;
&rfc3550;
&rfc3711;
&rfc2327;
&rfc4288;
&rfc4855;
&rfc3551;
</references>
</back>
</rfc>
<!-- LocalWords: PictureID DCT Hadamard WHT SSRC CSRC pyld hdr FI VER RPSI
-->
<!-- LocalWords: stPartitionSize SLI SDP AVPF SRTP IANA PartID PICIDX TID
-->
| PAFTECH AB 2003-2026 | 2026-04-23 19:38:08 |