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). Kerr Expires August 1, 2005 [Page 1] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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 Kerr Expires August 1, 2005 [Page 2] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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]. Kerr Expires August 1, 2005 [Page 3] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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 Kerr Expires August 1, 2005 [Page 4] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 5] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 6] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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: Kerr Expires August 1, 2005 [Page 7] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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 Kerr Expires August 1, 2005 [Page 8] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 9] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 10] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 11] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 12] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 13] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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: Kerr Expires August 1, 2005 [Page 14] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 15] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 16] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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]; Kerr Expires August 1, 2005 [Page 17] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 18] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 19] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 20] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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. Kerr Expires August 1, 2005 [Page 21] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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: 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 Kerr Expires August 1, 2005 [Page 22] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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: Kerr Expires August 1, 2005 [Page 23] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 Video streaming and conferencing tools Additional information: none Person & email address to contact for further information: Phil Kerr: 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= Kerr Expires August 1, 2005 [Page 24] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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). Kerr Expires August 1, 2005 [Page 25] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 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/ Kerr Expires August 1, 2005 [Page 26] Internet-Draft draft-kerr-avt-theora-rtp-00 January 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Kerr Expires August 1, 2005 [Page 27]