Recognizes if input is ogg or not.

[xiph.git] / theora / doc / draft-kerr-avt-theora-rtp-00.txt

AVT Working Group                                                P. Kerr
Internet-Draft                                                  Xiph.Org
Expires: August 1, 2005                                 January 31, 2005


                      draft-kerr-avt-theora-rtp-00
              RTP Payload Format for Theora Encoded Video

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 1, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes a RTP payload format for transporting Theora
   encoded video.  It details the RTP encapsulation mechanism for raw
   Theora data and configuration headers consisting of the quantization
   matrices and the Huffman codebooks for the DCT coefficients, and a
   table of limit values for the deblocking filter.

   Also included within the document are the necessary details for the
   use of Theora with MIME and Session Description Protocol (SDP).



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Editors Note

   All references to RFC XXXX are to be replaced by references to the
   RFC number of this memo, when published.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1   Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Payload Format . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1   RTP Header . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2   Payload Header . . . . . . . . . . . . . . . . . . . . . .  5
     2.3   Payload Data . . . . . . . . . . . . . . . . . . . . . . .  6
     2.4   Example RTP Packet . . . . . . . . . . . . . . . . . . . .  7
   3.  Frame Packetizing  . . . . . . . . . . . . . . . . . . . . . .  8
     3.1   Example Fragmented Theora Packet . . . . . . . . . . . . .  9
   4.  Packet Loss  . . . . . . . . . . . . . . . . . . . . . . . . . 12
   5.  Configuration Headers  . . . . . . . . . . . . . . . . . . . . 13
     5.1   In-band Header Transmission  . . . . . . . . . . . . . . . 13
       5.1.1   Identification Header  . . . . . . . . . . . . . . . . 13
       5.1.2   Comment Header . . . . . . . . . . . . . . . . . . . . 15
       5.1.3   Setup Header . . . . . . . . . . . . . . . . . . . . . 16
     5.2   Packed Headers Delivery  . . . . . . . . . . . . . . . . . 18
       5.2.1   Packed Headers IANA Considerations . . . . . . . . . . 21
     5.3   Setup Header Caching . . . . . . . . . . . . . . . . . . . 22
     5.4   Loss of Configuration Headers  . . . . . . . . . . . . . . 22
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
     6.1   Mapping MIME Parameters into SDP . . . . . . . . . . . . . 24
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 25
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
   9.1   Normative References . . . . . . . . . . . . . . . . . . . . 25
   9.2   Informative References . . . . . . . . . . . . . . . . . . . 26
       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 26
       Intellectual Property and Copyright Statements . . . . . . . . 27
















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1.  Introduction

   Theora is a general purpose, lossy video codec.  It is based on the
   VP3.1 video codec produced by On2 Technologies and has been donated
   to the Xiph.org Foundation.

   Theora I is a block-based lossy transform codec that utilizes an 8 x
   8 Type-II Discrete Cosine Transform and block-based motion
   compensation.  This places it in the same class of codecs as MPEG-1,
   MPEG-2, MPEG-4, and H.263.  The details of how individual blocks are
   organized and how DCT coefficients are stored in the bitstream differ
   substantially from these codecs, however.  Theora supports only intra
   frames (I frames in MPEG) and inter frames (P frames in MPEG).

   Theora provides none of its own framing, synchronization, or
   protection against transmission errors.  Theora is a free-form
   variable bit rate (VBR) codec, and packets have no minimum size,
   maximum size, or fixed/expected size.  Theora packets are thus
   intended to be used with a transport mechanism that provides
   free-form framing, synchronization, positioning, and error correction
   in accordance with these design assumptions, such as Ogg [1].  or
   RTP/AVP [3].

   Theora I currently supports progressive video data of arbitrary
   dimensions at a constant frame rate in one of several YCbCr color
   spaces.  Three different chroma subsampling formats are supported:
   4:2:0, 4:2:2, and 4:4:4.  The Theora I format does not support
   interlaced material, variable frame rates, bit-depths larger than 8
   bits per component, nor alternate color spaces such as RGB or
   arbitrary multi-channel spaces.  Black and white content can be
   efficiently encoded, however, because the uniform chroma planes
   compress well.

   Theora is similar to Vorbis audio [9] in that it requires the
   inclusion of the entire probability model for the DCT coefficients
   and all the quantization parameters in the bitstream headers to be
   sent ahead of the video data.  It is therefore impossible to decode
   any frame in the stream without having previously fetched the codec
   info and codec setup headers, although Theora can initiate decode at
   an arbitrary intra-frame packet within a bitstream so long as the
   codec has been initialized with the setup headers.

1.1  Terminology

   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 RFC 2119 [2].




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2.  Payload Format

   Each frame of digital video is packetized into one or more RTP
   packets.  If the data for a complete frame exceeds the network MTU,
   it SHOULD be fragmented into multiple RTP packets, each smaller than
   the MTU.  A single RTP packet MAY contain data for more than one
   Theora frame.

   For RTP based transportation of Theora encoded video the standard RTP
   header is followed by a 5 octet payload header, then the payload
   data.

2.1  RTP Header

   The format of the RTP header is specified in [3] and shown in Figure
   1.  This payload format uses the fields of the header in a manner
   consistent with that specification.

       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             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 1: RTP Header

   The RTP header begins with an octet of fields (V, P, X, and CC) to
   support specialized RTP uses (see [3] and [4] for details).  For
   Theora RTP, the following values are used.

   Version (V): 2 bits

   This field identifies the version of RTP.  The version used by this
   specification is two (2).

   Padding (P): 1 bit

   Padding MAY be used with this payload format according to section 5.1
   of [3].

   Extension (X): 1 bit



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   The Extension bit is used in accordance with [3].

   CSRC count (CC): 4 bits

   The CSRC count is used in accordance with [3].

   Marker (M): 1 bit

   The Marker bit is used in accordance with [3].

   Payload Type (PT): 7 bits

   An RTP profile for a class of applications is expected to assign a
   payload type for this format, or a dynamically allocated payload type
   SHOULD be chosen which designates the payload as Theora.

   Sequence number: 16 bits

   The sequence number increments by one for each RTP data packet sent,
   and may be used by the receiver to detect packet loss and to restore
   packet sequence.  This field is detailed further in [3].

   Timestamp: 32 bits

   A timestamp representing the sampling time of the first sample of the
   first Theora packet in the RTP packet.  The clock frequency MUST be
   set to the sample rate of the encoded video data and is conveyed
   out-of-band as an SDP attribute.

   SSRC/CSRC identifiers:

   These two fields, 32 bits each with one SSRC field and a maximum of
   16 CSRC fields, are as defined in [3].

2.2  Payload Header

   After the RTP Header section the following five octets are the
   Payload Header.  This header is split into a number of bitfields
   detailing the format of the following Payload Data packets.












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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |C|F|0|0|# pkts.|
      +-+-+-+-+-+-+-+-+

                        Figure 2: Payload Header

   Setup Header Ident: 32 bits

   This 32 bit field is used to associate the Theora data to a decoding
   Setup Header.  It is created by making a CRC32 checksum of the Setup
   Header required to decode the particular Theora video stream.

   Continuation (C): 1 bit

   Set to one if this is a continuation of a fragmented packet.

   Fragmented (F): 1 bit

   Set to one if the payload contains complete packets or if it contains
   the last fragment of a fragmented packet.

   The next two bits are currently reserved and MUST be set to 0.

   The last 4 bits are the number of complete packets in this payload.
   This provides for a maximum number of 15 Theora packets in the
   payload.  If the packet contains fragmented data the number of
   packets MUST be set to 0.

2.3  Payload Data

   Each Theora payload section starts with a three octet header.  The
   first octet is used to denote what kind of Theora data follows.  Then
   a two octet length header is used to represent the size of the
   following data payload, followed by the raw Theora data.













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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Data type   |        Payload Length         | Theora Data  ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 3: Payload Data

   The data type octet is used to signify the payload data type.  If the
   first bit is set to 0, this indicates the payload is Theora video
   data.

   The following values for the Theora payload type are valid:

      0 = Raw Theora data
      0x80 = Theora Identification header
      0x81 = Theora Comment header
      0x82 = Theora Setup header


   The Theora packet length header is the length of the Theora data
   block only and does not count the length octets and payload data type
   octet.

   The Theora codec uses relatively unstructured raw packets containing
   binary integer fields of arbitrary width that often do not fall on an
   octet boundary.  When this happens the bitstream is packed to an
   octet boundary.  When a Theora encoder produces packets unused space
   in the last byte of a packet is always zeroed during the encoding
   process.  Thus, should this unused space be read, it will return
   binary zeros.

   For payloads which consist of multiple Theora packets the payload
   data consists of the data type field, the payload length field
   followed by the payload data for each of the Theora packets in the
   payload.

2.4  Example RTP Packet

   Here is an example RTP packet containing two Theora packets.

   RTP Packet Header:









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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | 2 |0|0|  0    |0|      PT     |       sequence number         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 timestamp (in sample rate units)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          synchronisation source (SSRC) identifier             |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
      |            contributing source (CSRC) identifiers             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 4: Example RTP Packet

   Payload Data:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|1|0|0| 2 pks |      0x80     |        Payload Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Theora data                          ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..    data      |        0      |        Payload Length        ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                        Theora data                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 5: Example Theora Payload Packet

   The payload portion of the packet starts with the 32 bit Setup Header
   ident field followed by the 8 bit fragment/count fields.  The F bit
   is set to 1, indicating that this packet contains whole Theora frame
   data.  The number of whole Theora data packets is set to 2.

   Each of the payload blocks starts with a Data type field, for the
   first payload this is set to 0x80 indicating it is an Identification
   header and the second payload is set to 0 indicating it is raw Theora
   data.  Then the two octet length field is followed by the variable
   length Theora data.

3.  Frame Packetizing

   Each RTP packet contains either one complete Theora packet, one
   Theora packet fragment, or an integer number of complete Theora



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   packets (up to a max of 15 packets, since the number of packets is
   defined by a 4 bit value).

   Any Theora data packet that is less than path MTU SHOULD be bundled
   in the RTP packet with as many Theora packets as will fit, up to a
   maximum of 15.  Path MTU is detailed in [6] and [7].

   If a Theora packet is larger than 65535 octets it MUST be fragmented.
   A fragmented packet has a zero in the last four bits of the payload
   header.  Each fragment after the first will also set the Continued
   (C) bit to one in the payload header.  The RTP packet containing the
   last fragment of the Theora packet will have the Fragmented (F) bit
   set to one.  To maintain the correct sequence for fragmented packet
   reception the timestamp field of fragmented packets MUST be the same
   as the first packet sent, with the sequence number incremented as
   normal for the subsequent RTP packets.

3.1  Example Fragmented Theora Packet

   Here is an example fragmented Theora packet split over three RTP
   packets.  Each packet contains the standard RTP headers as well as
   the 5 octet Theora headers.





























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      Packet 1:

       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      |           1000                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             xxxxx                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           synchronization source (SSRC) identifier            |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
      |            contributing source (CSRC) identifiers             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|0|0|0|      0|       0       |        Payload Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Theora data                          ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 6: Example Fragmented Packet (Packet 1)

   In this packet the initial sequence number is 1000 and the timestamp
   is xxxxx.  The Continuation (C) bit is set to one, indicating it is
   not the continuation of a fragmented bit, and the Fragmentation (F)
   is set to 0 indicating it is a fragmented packet.  The number of
   packets field is set to 0, and as the payload is raw Theora data the
   Theora payload type field is set to 0.





















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      Packet 2:

       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      |           1001                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             xxxxx                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           synchronization source (SSRC) identifier            |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
      |            contributing source (CSRC) identifiers             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1|0|0|0|      0|       0       |        Payload Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Theora data                          ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 7: Example Fragmented Packet (Packet 2)

   The C bit is set to 1 and the number of packets field is set to 0.
   For large Theora fragments there can be several of these type of
   payload packets.  The maximum packet size SHOULD be no greater than
   the path MTU, including all RTP and payload headers.  The sequence
   number has been incremented by one but the timestamp field remains
   the same as the initial packet.





















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      Packet 3:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |V=2|P|X|  CC   |M|     PT      |           1002                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             xxxxx                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           synchronization source (SSRC) identifier            |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
      |            contributing source (CSRC) identifiers             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |1|1|0|0|      0|       0       |        Payload Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Theora data                          ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 8: Example Fragmented Packet (Packet 3)

   This is the last Theora fragment packet.  The C and F bits are set
   and the packet count remains set to 0.  As in the previous packets
   the timestamp remains set to the first packet in the sequence and the
   sequence number has been incremented.

4.  Packet Loss

   As there is no error correction within the Theora stream, packet loss
   will result in a loss of signal.  Packet loss is more of an issue for
   fragmented Theora packets as the client will have to cope with the
   handling of the C and F flags.  If we use the fragmented Theora
   packet example above and the first packet is lost the client SHOULD
   detect that the next packet has the packet count field set to 0 and
   the C bit is set and MUST drop it.  The next packet, which is the
   final fragmented packet, SHOULD be dropped in the same manner, or
   buffered.  Feedback reports on lost and dropped packets MUST be sent
   back via RTCP.

   If a particular multicast session has a large number of participants
   care must be taken to prevent an RTCP feedback implosion, [8], in the
   event of packet loss from a large number of participants.






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5.  Configuration Headers

   To decode a Theora stream three configuration header blocks are
   needed.  The first header, the Identification Header, indicates the
   frame dimensions, quality, blocks used and the version of the Theora
   encoder used.  The second header, the Comment Header, contains stream
   metadata and the third header, the Setup Header, details which
   contains dequantization and Huffman tables.

   As the RTP stream may change certain configuration data mid-session
   there are two different methods for delivering this configuration
   data to a client, in-band and SDP which is detailed below.  SDP
   delivery is used to set-up an initial state for the client
   application and in-band is used to change state during the session.
   The changes may be due to different metadata or Setup Header as well
   as different bitrates of the stream.

   Out of the two delivery vectors the use of an SDP attribute to
   indicate an URI where the configuration and Setup Header data can be
   obtained is preferred as they can be fetched reliably using TCP.  The
   in-band Setup Header delivery SHOULD only be used in situations where
   the link between the client is unidirectional or if the SDP-based
   information is not available.

   Synchronizing the configuration and Setup Header to the RTP stream is
   critical.  The 32 bit Setup Header Ident field is used to indicate
   when a change in the stream has taken place.  The client application
   MUST have in advance the correct configuration and Setup Headers and
   if the client detects a change in the Ident value and does not have
   this information it MUST NOT decode the raw Theora data.

5.1  In-band Header Transmission

   The three header data blocks are sent in-band with the packet type
   bits set to match the payload type.  Normally the Setup Header and
   Identification Header are sent once per session if the stream is an
   encoding of live video, as typically the encoder state will not
   change, but the encoder state can change at the boundary of chained
   Theora video files.  Metadata can be sent at the start as well as any
   time during the life of the session.  Clients MUST be capable of
   dealing with periodic re-transmission of the configuration headers.

5.1.1  Identification Header

   The Identification Header is a short header with only a few fields
   used to declare the stream definitively as Theora and provide
   detailed information about the format of the fully decoded video
   data.



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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |V=2|P|X|  CC   |M|     PT      |             xxxx              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             xxxxx                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           synchronization source (SSRC) identifier            |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
      |            contributing source (CSRC) identifiers             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|1|0|0|      1|     0x80      |        Payload Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     VMAJ      |     VMIN      |     VREV      |     FMBW      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     FMBW      |              FMBH             |     NSBS      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     NSBS                      |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       NBS                             | NMBS  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       NMBS                            | PICW  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              PICW             |             PICH              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PICH  |     PICX      |      PICY     |         FRN           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                FRN                    |         FRD           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                FRD                    |         PARN          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         PARN          |               PARD                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PARD  |      CS       |PF |             NOMBR                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   NOMBR   |   QUAL    | KFGSHIFT|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 9: Identification Header

   The fields listed above have the following meanings:






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      VMAJ     = The major version number.  8 bits.
      VMIN     = The minor version number.  8 bits.
      VREV     = The version revision number.  8 bits.
      FMBW     = The width of the frame in macro blocks.  16 bits.
      FMBH     = The height of the frame in macro blocks.  16 bits.
      NSBS     = The total number of super blocks in a frame.  32 bits.
      NBS      = The total number of blocks in a frame.  36 bits.
      NMBS     = The total number of macro blocks in a frame.  32 bits.
      PICW     = The width of the picture region in pixels.  20 bits.
      PICH     = The height of the picture region in pixels.  20 bits.
      PICX     = The X offset of the picture region in pixels.  8 bits.
      PICY     = The Y offset of the picture region in pixels.  8 bits.
      FRN      = The frame-rate numerator.  32 bits.
      FRD      = The frame-rate denominator.  32 bits.
      PARN     = The pixel aspect-ratio numerator.  24 bits.
      PARD     = The pixel aspect-ratio denominator.  24 bits.
      CS       = The color space.  8 bits.
      PF       = The pixel format.  2 bits.
      NOMBR    = The nominal bitrate of the stream, in bits per second.
      24 bits.
      QUAL     = The quality hint.  6 bits.
      KFGSHIFT = The amount to shift the key frame number by in the
      granule position.  5 bits.


5.1.2  Comment Header

   The Theora Comment Header is the second of three header packets that
   begin a Theora stream.  It is meant for short text comments, not
   arbitrary metadata; arbitrary metadata belongs in a separate logical
   stream that provides greater structure and machine parseability.  The
   comment field is meant to be used much like someone jotting a quick
   note on the label of a video.  It should be a little information to
   remember the disc or tape by and explain it to others; a short,
   to-the-point text note that can be more than a couple words, but
   isn't going to be more than a short paragraph.















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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |V=2|P|X|  CC   |M|     PT      |             xxxx              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             xxxxx                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           synchronization source (SSRC) identifier            |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
      |            contributing source (CSRC) identifiers             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|1|0|0|      1|     0x81      |        Payload Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    User comments list length                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       User comment length                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User comment                        ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                         User comment                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                       Figure 10: Comment Header

   The format for the data takes the form of a 32 bit field denoting the
   number of user comments.  Each of the user comments is prefixed by a
   32 bit length field followed by the comment text encoded in UTF-8.

5.1.3  Setup Header

   The Theora setup header contains the limit values used to drive the
   loop filter, the base matrices and scale values used to build the
   dequantization tables, and the Huffman tables used to unpack the DCT
   tokens.  Because the contents of this header are specific to Theora,
   no concessions have been made to keep the fields octet-aligned for
   easy parsing.









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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |V=2|P|X|  CC   |M|     PT      |             xxxx              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             xxxxx                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           synchronization source (SSRC) identifier            |
      +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
      |            contributing source (CSRC) identifiers             |
      |                              ...                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|1|0|0|      1|     0x82      |        Payload Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Setup Header Length                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Setup Header                         ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                        Setup Header                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 11: Setup Header


5.1.3.1  Setup Header CRC32 Generation

   In order for different implementations of Theora RTP clients and
   servers to interoperate with each other a common format for the
   production of the CRC32 hash is required.  The polynomial is
   X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0.

   The following C code function SHOULD be used by implementations, if
   not then the code responsible for generating the CRC32 value MUST use
   the polynomial function above.

   unsigned int crc32 (int length, unsigned char *crcdata)
   {
       int index, loop;
       unsigned int byte, crc, mask;

       index = 0;
       crc = 0xFFFFFFFF;

       while (index < length) {
           byte = crcdata [index];



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           crc = crc ^ byte;

           for (loop = 7; loop >= 0; loop--) {
               mask = -(crc & 1);
               crc = (crc >> 1) ^ (0xEDB88320 & mask);
           }
           index++;
       }
       return ~crc;
   }


5.2  Packed Headers Delivery

   As mentioned above the RECOMMENDED delivery vector for Theora
   configuration data is via an SDP attribute as this retrieval method
   can be performed using a reliable transport protocol.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Number of packed headers                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Packed header                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Packed header                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 12: Packed Headers Overview

   As the RTP headers are not required for this method of delivery the
   structure of the configuration data is slightly different.  The
   packed header starts with a 32 bit count field which details the
   number of packed headers that are contained in the bundle.  Next is
   the packed header payload for each chained Theora file.
















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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Header Length                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Setup Header Ident                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Identification Header                    ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                    Identification Header                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Comment Header                       ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                        Comment Header                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Setup Header                        ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                         Setup Header                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 13: Packed Headers Detail

   The key difference between the in-band format is there is no need for
   the payload header octet and Setup Header Ident field.  Below are
   examples of the packed headers format.


























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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     VMAJ      |     VMIN      |     VREV      |     FMBW      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     FMBW      |              FMBH             |     NSBS      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     NSBS                      |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       NBS                             | NMBS  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       NMBS                            | PICW  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              PICW             |             PICH              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PICH  |     PICX      |      PICY     |         FRN           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                FRN                    |         FRD           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                FRD                    |         PARN          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         PARN          |               PARD                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | PARD  |      CS       |PF |             NOMBR                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   NOMBR   |   QUAL    | KFGSHIFT|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 14: Packed Identification Header

   The alignment of the packed Identification Header is slightly
   different from the RTP payload type as the payload header is not
   used.


















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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    User comments list length                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       User comment length                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          User comment                        ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                         User comment                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 15: Packed Comment Header

   The packed Comment Header also as a slightly different structure to
   that of the RTP payload type with the payload header not being used.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Setup Header Length                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Setup Header                         ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ..                        Setup Header                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 16: Packed Setup Header

   The packed Setup Header also has a slightly different structure to
   that of the RTP payload type.  The Setup Header Ident field that is
   normally part of this structure is moved to the second field of the
   overall packed structure.

5.2.1  Packed Headers IANA Considerations

   The following IANA considerations MUST only be applied to the packed
   headers.

   MIME media type name: video

   MIME subtype: theora-config

   Required Parameters:

   None.




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   Optional Parameters:

   None.

   Encoding considerations:

   This type is only defined for transfer via HTTP as specified in RFC
   XXXX.

   Security Considerations:

   See Section 6 of RFC 3047.

   Interoperability considerations: none

   Published specification:

   See RFC XXXX for details.

   Applications which use this media type:

   Theora encoded video, configuration data.

   Additional information: none

   Person & email address to contact for further information:

   Phil Kerr: <phil@plus24.com>

   Intended usage: COMMON

   Author/Change controller:

   Author: Phil Kerr

   Change controller: IETF AVT Working Group

5.3  Setup Header Caching

   Setup Header caching allows clients that have previously connected to
   a stream to re-use the associated Setup Header and configuration
   data.  When a client receives a Setup Header it may store it locally
   and can compare the CRC32 key with that of the new stream and begin
   decoding before it has received any of the headers.

5.4  Loss of Configuration Headers

   Unlike the loss of raw Theora payload data, loss of a configuration



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   header can lead to a situation where it will not be possible to
   successfully decode the stream.

   Out of the three headers, loss of either the Setup Header or
   Identification Headers MUST result in the halting of stream decoding.
   Loss of the Comment header SHOULD NOT be regarded as fatal for
   decoding.  Loss of any of the headers SHOULD be reported to the
   client as well as a loss report sent via RTCP.

6.  IANA Considerations

   MIME media type name: video

   MIME subtype: theora

   Required Parameters:

   sampling: Determines the chroma subsampling format.

   width: Determines the number of pixels per line.  This is an integer
   between 1 and 1048561 and MUST be in multiples of 16.

   height: Determines the number of lines per frame.  This is an integer
   between 1 and 1048561 and MUST be in multiples of 16.

   header: Indicates the URI of the decoding configuration headers.

   Optional Parameters:

   None.

   Encoding considerations:

   This type is only defined for transfer via RTP as specified in RFC
   XXXX.

   Security Considerations:

   See Section 6 of RFC 3047.

   Interoperability considerations: none

   Published specification:

   See the Theora documentation [11] for details.

   Applications which use this media type:




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   Video streaming and conferencing tools

   Additional information: none

   Person & email address to contact for further information:

   Phil Kerr: <phil@plus24.com>

   Intended usage: COMMON

   Author/Change controller:

   Author: Phil Kerr

   Change controller: IETF AVT Working Group

6.1  Mapping MIME Parameters into SDP

   The information carried in the MIME media type specification has a
   specific mapping to fields in the Session Description Protocol (SDP)
   [5], which is commonly used to describe RTP sessions.  When SDP is
   used to specify sessions the mapping are as follows:

   o  The MIME type ("video") goes in SDP "m=" as the media name.

   o  The MIME subtype ("THEORA") goes in SDP "a=rtpmap" as the encoding
      name.

   o  The parameter "rate" also goes in "a=rtpmap" as clock rate.

   o  The parameter "channels" also goes in "a=rtpmap" as channel count.

   o  The parameter "header" goes in the SDP "a=fmpt" attribute.

   If the stream comprises chained Theora files the configuration and
   Setup Headers for each file SHOULD be packaged together and passed to
   the client using the headers attribute if all the files to be played
   are known in advance.

   Example:

      c=IN IP4/6
      m=video  RTP/AVP 98
      a=rtpmap:98 theora/90000
      a=fmtp:98 sampling=YCbCr-4:2:2; width=1280; height=720;
      header=<URI of configuration header>





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7.  Security Considerations

   RTP packets using this payload format are subject to the security
   considerations discussed in the RTP specification [3].  This implies
   that the confidentiality of the media stream is achieved by using
   encryption.  Because the data compression used with this payload
   format is applied end-to-end, encryption may be performed on the
   compressed data.  Where the size of a data block is set care MUST be
   taken to prevent buffer overflows in the client applications.

8.  Acknowledgments

   Thanks to the AVT, Ogg Theora Communities / Xiph.org, Fluendo, Ralph
   Giles.

9.  References

9.1  Normative References

   [1]  Pfeiffer, S., "The Ogg Encapsulation Format Version 0", RFC
        3533.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119.

   [3]  Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
        "RTP: A Transport Protocol for real-time applications", RFC
        3550.

   [4]  Schulzrinne, H. and S. Casner, "RTP Profile for video and Video
        Conferences with Minimal Control.", RFC 3551.

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

   [6]  Mogul et al., J., "Path MTU Discovery", RFC 1063.

   [7]  McCann et al., J., "Path MTU Discovery for IP version 6", RFC
        1981.

   [8]  Ott, J., Wenger, S., Sato, N., Burmeister, C. and J. Rey,
        "Extended RTP Profile for RTCP-based Feedback (RTP/AVPF)",
        Internet Draft (draft-ietf-avt-rtcp-feedback-11: Work in
        progress).

   [9]  Kerr, P., "RTP Payload Format for Vorbis Encoded Audio -
        draft-ietf-avt-vorbis-rtp-00", Internet Draft (Work in
        progress).



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9.2  Informative References

   [10]  "libTheora: Available from the Xiph website,
         http://www.xiph.org".

   [11]  "Ogg Theora I spec:  Codec setup and packet decode.
         http://www.xiph.org/ogg/Theora/doc/Theora-spec-ref.html".


Author's Address

   Phil Kerr
   Xiph.Org

   EMail: phil@plus24.com
   URI:   http://www.xiph.org/



































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