-AVT Working Group P. Kerr
+
+
+AVT Working Group L. Barbato
Internet-Draft Xiph.Org
-Expires: August 1, 2005 January 31, 2005
+Expires: April 24, 2006 October 21, 2005
- draft-ietf-avt-vorbis-rtp-00
+ draft-kerr-avt-vorbis-rtp-05
RTP Payload Format for Vorbis Encoded Audio
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.
+ 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 becomes
+ aware will be disclosed, in accordance with Section 6 of BCP 79.
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.
+ 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
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.
+ This Internet-Draft will expire on April 24, 2006.
Copyright Notice
This document describes an RTP payload format for transporting Vorbis
encoded audio. It details the RTP encapsulation mechanism for raw
Vorbis data and details the delivery mechanisms for the decoder
- probability model, referred to as a codebook, metadata and other
- setup information.
+ probability model, referred to as a codebook and other setup
+ information.
Also included within the document are the necessary details for the
use of Vorbis 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
+ 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 3
- 2.1 RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 3
- 2.2 Payload Header . . . . . . . . . . . . . . . . . . . . . . 5
- 2.3 Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6
- 2.4 Example RTP Packet . . . . . . . . . . . . . . . . . . . . 7
- 3. Frame Packetizing . . . . . . . . . . . . . . . . . . . . . . 8
- 3.1 Example Fragmented Vorbis Packet . . . . . . . . . . . . . 8
- 3.2 Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 11
- 4. Configuration Headers . . . . . . . . . . . . . . . . . . . . 12
- 4.1 In-band Header Transmission . . . . . . . . . . . . . . . 12
- 4.1.1 Setup Header . . . . . . . . . . . . . . . . . . . . . 13
- 4.1.2 Codebook Header . . . . . . . . . . . . . . . . . . . 13
- 4.1.3 Metadata Header . . . . . . . . . . . . . . . . . . . 15
- 4.2 Packed Headers Delivery . . . . . . . . . . . . . . . . . 16
- 4.2.1 Packed Headers IANA Considerations . . . . . . . . . . 19
- 4.3 Codebook Caching . . . . . . . . . . . . . . . . . . . . . 20
- 4.4 Loss of Configuration Headers . . . . . . . . . . . . . . 20
- 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
- 5.1 Mapping MIME Parameters into SDP . . . . . . . . . . . . . 21
- 6. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 22
- 7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
- 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
- 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
- 9.1 Normative References . . . . . . . . . . . . . . . . . . . . 23
- 9.2 Informative References . . . . . . . . . . . . . . . . . . . 24
- Author's Address . . . . . . . . . . . . . . . . . . . . . . . 24
- Intellectual Property and Copyright Statements . . . . . . . . 25
+ 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 3
+ 2.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 5
+ 2.3. Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6
+ 2.4. Example RTP Packet . . . . . . . . . . . . . . . . . . . . 7
+ 3. Configuration Headers . . . . . . . . . . . . . . . . . . . . 8
+ 3.1. In-band Header Transmission . . . . . . . . . . . . . . . 9
+ 3.1.1. Packed Configuration . . . . . . . . . . . . . . . . . 9
+ 3.2. Out of Band Transmission . . . . . . . . . . . . . . . . . 10
+ 3.2.1. Packed Headers . . . . . . . . . . . . . . . . . . . . 10
+ 3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 12
+ 4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 12
+ 5. Frame Packetizing . . . . . . . . . . . . . . . . . . . . . . 13
+ 5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 14
+ 5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 16
+ 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
+ 6.1. Mapping MIME Parameters into SDP . . . . . . . . . . . . . 18
+ 6.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 19
+ 7. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 19
+ 8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
+ 8.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 19
+ 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
+ 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
+ 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
+ 11.1. Normative References . . . . . . . . . . . . . . . . . . . 21
+ 11.2. Informative References . . . . . . . . . . . . . . . . . . 21
+ Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
+ Intellectual Property and Copyright Statements . . . . . . . . . . 24
-
-
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+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
1. Introduction
Vorbis is a general purpose perceptual audio codec intended to allow
maximum encoder flexibility, thus allowing it to scale competitively
- over an exceptionally wide range of bitrates. At the high
- quality/bitrate end of the scale (CD or DAT rate stereo, 16/24 bits),
- it is in the same league as MPEG-2 and MPC. Similarly, the 1.0
- encoder can encode high-quality CD and DAT rate stereo at below 48k
- bits/sec without resampling to a lower rate. Vorbis is also intended
- for lower and higher sample rates (from 8kHz telephony to 192kHz
- digital masters) and a range of channel representations (monaural,
- polyphonic, stereo, quadraphonic, 5.1, ambisonic, or up to 255
- discrete channels).
+ over an exceptionally wide range of bitrates. At the high quality/
+ bitrate end of the scale (CD or DAT rate stereo, 16/24 bits), it is
+ in the same league as MPEG-2 and MPC. Similarly, the version 1.1
+ reference encoder can encode high-quality CD and DAT rate stereo at
+ below 48k bits/sec without resampling to a lower rate. Vorbis is
+ also intended for lower and higher sample rates (from 8kHz telephony
+ to 192kHz digital masters) and a range of channel representations
+ (monaural, polyphonic, stereo, quadraphonic, 5.1, ambisonic, or up to
+ 255 discrete channels).
Vorbis encoded audio is generally encapsulated within an Ogg format
bitstream [1], which provides framing and synchronization. For the
purposes of RTP transport, this layer is unnecessary, and so raw
Vorbis packets are used in the payload.
-1.1 Terminology
+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].
+
2. Payload Format
For RTP based transportation of Vorbis encoded audio the standard RTP
- header is followed by a 5 octet payload header, then the payload
+ header is followed by a 4 octet payload header, then the payload
data. The payload headers are used to associate the Vorbis data with
its associated decoding codebooks as well as indicating if the
following packet contains fragmented Vorbis data and/or the the
number of whole Vorbis data frames. The payload data contains the
raw Vorbis bitstream information.
-2.1 RTP Header
+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.
+ Figure 1. This payload format uses the fields of the header in a
+ manner consistent with that specification.
-
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0 1 2 3
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 1: RTP Header
+ 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
Marker (M): 1 bit
Set to zero. Audio silence suppression not used. This conforms to
- section 4.1 of [11].
+ section 4.1 of [12].
Payload Type (PT): 7 bits
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Sequence number: 16 bits
A timestamp representing the sampling time of the first sample of the
first Vorbis packet in the RTP packet. The clock frequency MUST be
- set to the sample rate of the encoded audio data and is conveyed
- out-of-band as a SDP attribute.
+ set to the sample rate of the encoded audio data and is conveyed out-
+ of-band as a 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
+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.
+ After the RTP Header section the following 4 octets are the Payload
+ Header. This header is split into a number of bitfields detailing
+ the format of the following payload data packets.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
+ | Ident | F |VDT|# pkts.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |C|F|VDT|# pkts.|
- +-+-+-+-+-+-+-+-+
- Figure 2: Payload Header
+ Figure 2: Payload Header
- Codebook Ident: 32 bits
+ Ident: 24 bits
- This 32 bit field is used to associate the Vorbis data to a decoding
- Codebook. It is created by making a CRC32 checksum of the codebook
- required to decode the particular Vorbis audio stream.
+ This 24 bit field is used to associate the Vorbis data to a decoding
+ Configuration.
- Continuation (C): 1 bit
+ Fragment type (F): 2 bits
- Set to one if this is a continuation of a fragmented packet.
+ This field is set accordingly the following list
- Fragmented (F): 1 bit
+ 0 = Not Fragmented
+ 1 = Start Fragment
+ 2 = Continuation Fragment
+ 3 = End Fragment
- Set to one if the payload contains complete packets or if it contains
- the last fragment of a fragmented packet.
+ Vorbis Data Type (VDT): 2 bits
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- Vorbis Data Type (VDT): 2 bits
This field sets the packet payload type for the Vorbis data. There
- are currently four type of Vorbis payloads.
+ are currently three type of Vorbis payloads.
0 = Raw Vorbis payload
- 1 = Vorbis Setup payload
- 2 = Vorbis Codebook payload
- 3 = Vorbis Metadata payload
+ 1 = Vorbis Packed Configuration payload
+ 2 = Legacy Vorbis Comment payload
+ 3 = Reserved
The last 4 bits are the number of complete packets in this payload.
This provides for a maximum number of 15 Vorbis packets in the
payload. If the packet contains fragmented data the number of
packets MUST be set to 0.
-2.3 Payload Data
+2.3. Payload Data
Raw Vorbis packets are unbounded in length currently, although at
some future point there will likely be a practical limit placed on
them. Typical Vorbis packet sizes are from very small (2-3 bytes) to
- quite large (8-12 kilobytes). The reference implementation [10]
- typically produces packets less than ~800 bytes, except for the
- codebook header packets which are ~4-12 kilobytes. Within an RTP
- context the maximum Vorbis packet size, including the RTP and payload
- headers, SHOULD be kept below the path MTU to avoid packet
- fragmentation.
+ quite large (8-12 kilobytes). The reference implementation [11]
+ typically produces packets less than ~800 bytes, except for the setup
+ header packets which are ~4-12 kilobytes. Within an RTP context the
+ maximum packet size, including the RTP and payload headers, SHOULD be
+ kept below the path MTU to avoid packet fragmentation.
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
| length | vorbis packet data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 3: Payload Data Header
+ Figure 3: Payload Data Header
Each Vorbis payload packet starts with a two octet length header,
which is used to represent the size of the following data payload,
- followed by the raw Vorbis data.
+ followed by the raw Vorbis data padded to the nearest byte boundary.
For payloads which consist of multiple Vorbis packets the payload
data consists of the packet length followed by the packet data for
The Vorbis packet length header is the length of the Vorbis data
block only and does not count the length field.
- The payload packing of the Vorbis data packets SHOULD follow the
+ The payload packing of the Vorbis data packets MUST follow the
guidelines set-out in [4] where the oldest packet occurs immediately
+ after the RTP packet header.
+ Channel mapping of the audio is in accordance with the Vorbis I
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- after the RTP packet header.
- Channel mapping of the audio is in accordance with BS. 775-1 ITU-R
- [13].
+ Specification [12].
-2.4 Example RTP Packet
+2.4. Example RTP Packet
Here is an example RTP packet containing two Vorbis packets.
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 4: Example Packet (RTP Headers)
+ Figure 4: Example Packet (RTP Headers)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
+ | Ident | 0 | 0 | 2 pks |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |0|1| 0 | 2 pks | length | vorbis data ..
+ | length | vorbis data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 5: Example Packet (Payload Data)
+ Figure 5: Example Packet (Payload Data)
+
+ The payload data section of the RTP packet starts with the 24 bit
+ Ident field followed by the one octet bitfield header, which has the
+ number of Vorbis frames set to 2. Each of the Vorbis data frames is
+ prefixed by the two octet length field. The Packet Type and Fragment
+ Type are set to 0. The decode Configuration that will be used to
+ decode the packets is the one indexed by the ident value.
- The payload data section of the RTP packet starts with the 32 bit
- Codebook Ident field followed by the one octet configuration header,
- which has the number of Vorbis frames set to 2. Each of the Vorbis
- data frames is prefixed by the two octet length field.
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-3. Frame Packetizing
+3. Configuration Headers
- Each RTP packet contains either one complete Vorbis packet, one
- Vorbis packet fragment, or an integer number of complete Vorbis
- packets (up to a max of 15 packets, since the number of packets is
- defined by a 4 bit value).
+ Unlike other mainstream audio codecs Vorbis has no statically
+ configured probability model. Instead, it packs all entropy decoding
+ configuration, VQ and Huffman models into a data block that must be
+ transmitted to the decoder along with the compressed data. A decoder
+ also requires identification information detailing the number of
+ audio channels, bitrates and other information to configure itself
+ for a particular compressed data stream. These two blocks of
+ information are often referred to collectively as the "codebooks" for
+ a Vorbis stream, and are nominally included as special "header"
+ packets at the start of the compressed data.
+
+ Thus these two codebook header packets must be received by the
+ decoder before any audio data can be interpreted. In addition, the
+ Vorbis I specification [12] requires the presense of a comment header
+ packet which gives simple metadata about the stream. This
+ requirement poses problems in RTP, which is often used over
+ unreliable transports.
+
+ Since this information must be transmitted reliably and, as the RTP
+ stream may change certain configuration data mid-session, there are
+ different methods for delivering this configuration data to a client,
+ both in-band and out-of-band which is detailed below. SDP delivery
+ is used to setup an initial state for the client application. The
+ changes may be due to different codebooks as well as different
+ bitrates of the stream.
+
+ The delivery vectors in use are specified by an SDP attribute to
+ indicate the method and the optional URI where the Vorbis Packed
+ Configuration (Section 3.1.1) Packets could be fetched. Different
+ delivery methods MAY be advertised for the same session. The in-band
+ Configuration delivery SHOULD be considered as baseline, out-of-band
+ delivery methods that don't use RTP will not be described in this
+ document. For non chained streams, the Configuration delivery method
+ RECOMMENDED is inline the Packed Configuration (Section 3.1.1) in the
+ SDP as explained in the IANA considerations (Section 6.1) section.
+
+ The 24 bit Ident field is used to map which Configuration will be
+ used to decodea packet. When the Ident field changes, it indicates
+ that a change in the stream has taken place. The client application
+ MUST have in advance the correct configuration and if the client
+ detects a change in the Ident value and does not have this
+ information it MUST NOT decode the raw Vorbis data associated until
+ it fetches the correct Configuration.
+
+
+
+
+
+
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- Any Vorbis data packet that is less than path MTU SHOULD be bundled
- in the RTP packet with as many Vorbis packets as will fit, up to a
- maximum of 15. Path MTU is detailed in [6] and [7].
- If a Vorbis 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 Vorbis 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. In-band Header Transmission
-3.1 Example Fragmented Vorbis Packet
+ The Packed Configuration (Section 3.1.1) Payload is sent in-band with
+ the packet type bits set to match the payload type. Clients MUST be
+ capable of dealing with fragmentation and periodic re-transmission of
+ the configuration headers.
- Here is an example fragmented Vorbis packet split over three RTP
- packets. Each packet contains the standard RTP headers as well as
- the 5 octet Vorbis headers.
+3.1.1. Packed Configuration
+ A Vorbis Packed Configuration is indicated with the payload type
+ field set to 1. Of the three headers, defined in the Vorbis I
+ specification [12], the identification and the setup will be packed
+ together, the comment header is completely suppressed. Is up to the
+ client provide a minimal size comment header to the decoder if
+ required by the implementation.
+ 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 |
+ | ... |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Ident | 0 | 1 | 1|
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | length | Identification ..
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. Identification ..
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. Identification ..
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. Identification ..
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. | Setup ..
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. Setup ..
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. Setup |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Figure 6: Packed Configuration Figure
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+ The Ident field is set with the value that will be used by the Raw
+ Payload Packets to address this Configuration. The Fragment type is
+ set to 0 since the packet bears the full Packed configuration, the
+ number of packet is set to 1.
+3.2. Out of Band Transmission
+ This section, as stated before, won't cover all the possible out-of-
+ band delivery methods since they rely to different protocols and be
+ linked to a specific application. The following packet definition
+ SHOULD be used in out-of-band delivery and MUST be used when
+ Configuration is inlined in the SDP.
+3.2.1. Packed Headers
+ As mentioned above the RECOMMENDED delivery vector for Vorbis
+ configuration data is via a retrieval method that can be performed
+ using a reliable transport protocol. 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 Vorbis stream.
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Number of packed headers |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Packed header |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Packed header |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Figure 7: Packed Headers Overview
+ Since the Configuration Ident and the Identification Header are fixed
+ length there is only a 2 byte length tag to define the length of the
+ packed headers.
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- Packet 1:
+
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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 | 1000 |
+ | Ident | ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | xxxxx |
+ .. length | Identification Header ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | synchronization source (SSRC) identifier |
- +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
- | contributing source (CSRC) identifiers |
- | ... |
+ .. Identification Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Setup Header ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |0|0| 0 | 0| length | vorbis data ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. vorbis data |
+ .. Setup Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- 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 Vorbis data the
- VDT field is set to 0.
+ Figure 8: Packed Headers Detail
+ The key difference between the in-band format and this one, is there
+ is no need for the payload header octet.
+3.2.1.1. Packed Headers IANA Considerations
+ The following IANA considerations MUST only be applied to the packed
+ headers.
+ MIME media type name: audio
+ MIME subtype: vorbis-config
+ Required Parameters:
+ None.
+ Optional Parameters:
+ None.
+ Encoding considerations:
+ This type is only defined for transfer via non RTP protocols as
+ specified in RFC XXXX.
+ Security Considerations:
+ See Section 6 of RFC 3047.
+ Interoperability considerations: none
+ Published specification:
+Barbato Expires April 24, 2006 [Page 11]
+\f
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
+ See RFC XXXX for details.
-Kerr Expires August 1, 2005 [Page 9]
-\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+ Applications which use this media type:
+ Vorbis encoded audio, configuration data.
- Packet 2:
+ Additional information: none
- 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 |
- | ... |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |1|0| 0 | 0| length | vorbis data ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. vorbis data |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Person & email address to contact for further information:
- Figure 7: Example Fragmented Packet (Packet 2)
+ Luca Barbato: <lu_zero@gentoo.org>
- The C bit is set to 1 and the number of packets field is set to 0.
- For large Vorbis 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.
+ Intended usage: COMMON
+ Author/Change controller:
+ Author: Luca Barbato
+ Change controller: IETF AVT Working Group
+3.3. Loss of Configuration Headers
+ Unlike the loss of raw Vorbis payload data, loss of a configuration
+ header can lead to a situation where it will not be possible to
+ successfully decode the stream.
+ Loss of Configuration Packet results in the halting of stream
+ decoding and SHOULD be reported to the client as well as a loss
+ report sent via RTCP.
+4. Comment Headers
+ With the payload type flag set to 2, this indicates that the packet
+ contain the comment metadata, such as artist name, track title and so
+ on. These metadata messages are not intended to be fully descriptive
+ but to offer basic track/song information. Clients MAY ignore it
+ completely. The details on the format of the comments can be found
+ in the Vorbis documentation [12].
-Kerr Expires August 1, 2005 [Page 10]
+Barbato Expires April 24, 2006 [Page 12]
\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 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 |
+ |V=2|P|X| CC |M| PT | xxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| xxxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
+ | Ident | 0 | 2 | 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |1|1| 0 | 0| length | vorbis data ..
+ | length | Comment ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. vorbis data |
+ .. Comment ..
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. Comment |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 8: Example Fragmented Packet (Packet 3)
+ Figure 9: Comment Packet
- This is the last Vorbis 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.
+ The 2 bytes length field is necessary since this packet could be
+ fragmented.
-3.2 Packet Loss
- As there is no error correction within the Vorbis stream, packet loss
- will result in a loss of signal. Packet loss is more of an issue for
- fragmented Vorbis packets as the client will have to cope with the
- handling of the C and F flags. If we use the fragmented Vorbis
- 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.
+5. Frame Packetizing
- If a particular multicast session has a large number of participants
- care must be taken to prevent an RTCP feedback implosion, [9], in the
- event of packet loss from a large number of participants.
+ Each RTP packet contains either one Vorbis packet fragment, or an
+ integer number of complete Vorbis packets (up to a max of 15 packets,
+ since the number of packets is defined by a 4 bit value).
- Loss of any of the configuration headers, detailed below, is dealt
- with in the Loss of Configuration Headers Section later.
+ Any Vorbis data packet that is less than path MTU SHOULD be bundled
+ in the RTP packet with as many Vorbis packets as will fit, up to a
+ maximum of 15. Path MTU is detailed in [6] and [7].
+ If a Vorbis packet, not only data but also Configuration and Comment,
+ is larger than 65535 octets it MUST be fragmented. A fragmented
+ packet has a zero in the last four bits of the payload header. The
+ first fragment will set the Fragment type to 1. Each fragment after
+ the first will set the Fragment type to 2 in the payload header. The
+ RTP packet containing the last fragment of the Vorbis packet will
+ have the Fragment type set to 3. 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. The
-Kerr Expires August 1, 2005 [Page 11]
-\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+Barbato Expires April 24, 2006 [Page 13]
+\f
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
-4. Configuration Headers
- Unlike other mainstream audio codecs Vorbis has no statically
- configured probability model, instead it packs all entropy decoding
- configuration, VQ and Huffman models into a self-contained codebook.
- This codebook block also requires additional identification
- information detailing the number of audio channels, bitrates and
- other information used to initialise the Vorbis stream.
-
- To decode a Vorbis stream three configuration header blocks are
- needed. The first header indicates the sample and bitrates, the
- number of channels and the version of the Vorbis encoder used. The
- second header contains the decoders probability model, or codebook
- and the third header details stream metadata.
-
- 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 codebooks 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 codebook data can be
- obtained is preferred as they can be fetched reliably using TCP. The
- in-band codebook 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 codebook headers to the RTP
- stream is critical. The 32 bit Codebook 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
- codebook headers and if the client detects a change in the Ident
- value and does not have this information it MUST NOT decode the raw
- Vorbis data.
-
-4.1 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 codebook and
- configuration headers are sent once per session if the stream is an
- encoding of live audio, as typically the encoder state will not
- change, but the encoder state can change at the boundary of chained
- Vorbis audio 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.
-
-
-
-Kerr Expires August 1, 2005 [Page 12]
-\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+ length field shows the fragment length.
+5.1. Example Fragmented Vorbis Packet
-4.1.1 Setup Header
+ Here is an example fragmented Vorbis packet split over three RTP
+ packets. Each packet contains the standard RTP headers as well as
+ the 4 octet Vorbis headers.
- A Vorbis Setup header is indicated with the payload type field set to
- 1. The Vorbis version MUST be set to zero to comply with this
- document. The fields Sample Rate, Bitrate Maximum/Nominal/Minimum
- and Num Audio Channels are set in accordance with [11] with the bsz
- fields above referring to the blocksize parameters. The framing bit
- is not used for RTP transportation and so applications constructing
- Vorbis files MUST take care to set this if required.
+ 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 | xxxx |
+ |V=2|P|X| CC |M| PT | 1000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| xxxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |0|1| 2 | 1| bsz 0 | bsz 1 | Num Audio Channels |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Vorbis Version |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Audio Sample Rate |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bitrate Maximum |
+ | Ident | 1 | 0 | 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bitrate Nominal |
+ | length | vorbis data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bitrate Minimum |
+ .. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 9: Setup Header
+ Figure 10: Example Fragmented Packet (Packet 1)
+
+ In this packet the initial sequence number is 1000 and the timestamp
+ is xxxxx. The Fragment type is set to 1, the number of packets field
+ is set to 0, and as the payload is raw Vorbis data the VDT field is
+ set to 0.
+
+
-4.1.2 Codebook Header
- If the payload type field is set to 2, this indicates the packet
- contains Codebook data.
- The configuration information detailed below MUST be completely
- intact, as a client can not decode a stream with an incomplete or
-Kerr Expires August 1, 2005 [Page 13]
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-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
- corrupted codebook set.
- A 16 bit codebook length field precedes the codebook datablock. The
- length field allows for codebooks to be up to 64K in size. Packet
- fragmentation, as per the Vorbis data, MUST be performed if the
- codebooks size exceeds path MTU. The Codebook Ident field MUST be
- set to match the associated codebook needed to decode the Vorbis
- stream.
- The Codebook Ident is the CRC32 checksum of the codebook and is used
- to detect a corrupted codebook as well as associating it with its
- Vorbis data stream. This Ident value MUST NOT be set to the value of
- the current stream if this header is being sent before the boundary
- of the chained file has been reached. If a checksum failure is
- detected then this is considered to be a failure and MUST be reported
- to the client application.
+
+
+Barbato Expires April 24, 2006 [Page 14]
+\f
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 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 | xxxx |
+ |V=2|P|X| CC |M| PT | 1001 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| xxxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |0|1| 2 | 1| Codebook Length |
+ | Ident | 2 | 0 | 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | length | Codebook ..
+ | length | vorbis data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. Codebook |
+ .. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 10: Codebook Header
+ Figure 11: Example Fragmented Packet (Packet 2)
+ The Fragment type field is set to 2 and the number of packets field
+ is set to 0. For large Vorbis 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.
-4.1.2.1 Codebook CRC32 Generation
- In order for different implementations of Vorbis 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.
-Kerr Expires August 1, 2005 [Page 14]
-\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
- 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];
- crc = crc ^ byte;
- for (loop = 7; loop >= 0; loop--) {
- mask = -(crc & 1);
- crc = (crc >> 1) ^ (0xEDB88320 & mask);
- }
- index++;
- }
- return ~crc;
- }
-4.1.3 Metadata Header
- With the payload type flag set to 3, this indicates that the packet
- contain the comment metadata, such as artist name, track title and so
- on. These metadata messages are not intended to be fully descriptive
- but to offer basic track/song information. This message MUST be sent
- at the start of the stream, together with the setup and codebook
- headers, even if it contains no information. During a session the
- metadata associated with the stream may change from that specified at
- the start, e.g. a live concert broadcast changing acts/scenes, so
- clients MUST have the ability to receive Metadata header blocks.
- Details on the format of the comments can be found in the Vorbis
- documentation [12].
- The format for the data takes the form of a 32 bit codec vendors name
- length field followed by the name encoded in UTF-8. The next 32 bit
- field denotes the number of user comments. Each of the user comments
- is prefixed by a 32 bit length field followed by the comment text.
-
-Kerr Expires August 1, 2005 [Page 15]
+Barbato Expires April 24, 2006 [Page 15]
\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 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 | xxxx |
+ |V=2|P|X| CC |M| PT | 1002 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| xxxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |0|1| 3 | 1| Vendor string length |
+ | Ident | 3 | 0 | 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | length | Vendor string ..
+ | length | vorbis data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | User comments list length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | User comment length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | User comment ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. User comment |
+ .. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 11: Metadata Header
+ Figure 12: Example Fragmented Packet (Packet 3)
+ This is the last Vorbis fragment packet. The Fragment type is set to
+ 3 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.
-4.2 Packed Headers Delivery
+5.2. Packet Loss
- As mentioned above the RECOMMENDED delivery vector for Vorbis
- configuration data is via an SDP attribute as this retrieval method
- can be performed using a reliable transport protocol.
+ As there is no error correction within the Vorbis stream, packet loss
+ will result in a loss of signal. Packet loss is more of an issue for
+ fragmented Vorbis packets as the client will have to cope with the
+ handling of the Fragment Type. In case of loss of fragments the
+ client MUST discard all the remaining fragments and decode the
+ incomplete packet. If we use the fragmented Vorbis packet example
+ above and the first packet is lost the client MUST detect that the
+ next packet has the packet count field set to 0 and the Fragment type
+ 2 and MUST drop it. The next packet, which is the final fragmented
+ packet, MUST be dropped in the same manner. If the missing packet is
+ the last, the received two fragments will be kept and the incomplete
+ vorbis packet decoded. 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, [10], in
+ the event of packet loss from a large number of participants.
+Barbato Expires April 24, 2006 [Page 16]
+\f
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
+ Loss of any of the Configuration fragment will result in the loss of
+ the full Configuration packet with the result detailed in the Loss of
+ Configuration Headers (Section 3.3) section.
+6. IANA Considerations
+ MIME media type name: audio
+ MIME subtype: vorbis
+ Required Parameters:
+ delivery-method: indicates the delivery methods in use, the possible
+ values are:inline, in_band, out_band
+ configuration: the base16 [9] (hexadecimal) representation of the
+ Packed Headers (Section 3.2.1).
-Kerr Expires August 1, 2005 [Page 16]
-\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+ Optional Parameters:
+ configuration-uri: the URI of the configuration headers in case of
+ out of band transmission. In the form of
+ "protocol://path/to/resource/". Depending on the specific method the
+ single ident packet could be retrived by their number, or aggregated
+ in a single stream.
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Number of packed headers |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Packed header |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Packed header |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Encoding considerations:
- Figure 12: Packed Headers Overview
+ This type is only defined for transfer via RTP as specified in RFC
+ XXXX.
- 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 Vorbis file.
+ Security Considerations:
- 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 |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Ident |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Setup Header ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. Setup Header |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Header ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. Codebook Header |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Metadata Header ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. Metadata Header |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ See Section 6 of RFC 3047.
- Figure 13: Packed Headers Detail
+ Interoperability considerations: none
- The key difference between the in-band format is there is no need for
- the payload header octet and Codebook Ident field. Below are
- examples of the packed headers format.
+ Published specification:
+ See the Vorbis documentation [12] for details.
+ Applications which use this media type:
+ Audio streaming and conferencing tools
+ Additional information: none
-Kerr Expires August 1, 2005 [Page 17]
+Barbato Expires April 24, 2006 [Page 17]
\f
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+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 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
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- |0|1| 2 | 1| bsz 0 | bsz 1 | Num Audio Channels |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Vorbis Version |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Audio Sample Rate |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bitrate Maximum |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bitrate Nominal |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Bitrate Minimum |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Person & email address to contact for further information:
- Figure 14: Packed Setup Header
+ Luca Barbato: <lu_zero@gentoo.org>
- The alignment of the packed Setup Header is slightly different from
- the RTP payload type as the payload header is not used.
+ Intended usage: COMMON
- 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
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook Length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Codebook ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. Codebook |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ Author/Change controller:
- Figure 15: Packed Codebook Header
+ Author: Luca Barbato
- The packed Codebook header also has a slightly different structure to
- that of the RTP payload type. The Codebook Ident field that is
- normally part of this structure is moved to the second field of the
- overall packed structure.
+ 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 ("audio") goes in SDP "m=" as the media name.
+ o The MIME subtype ("vorbis") 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 mandated parameters "delivery-method" and "configuration" MUST
+ be included in the SDP "a=fmpt" attribute.
+ o The optional parameter "configuration-uri", when present, MUST be
+ included in the SDP "a=fmpt" attribute.
+ If the stream comprises chained Vorbis files and all of them are
+ known in advance, the Configuration Packet for each file SHOULD be
+ passed to the client using the configuration attribute.
+ The URI specified in the configuration-uri attribute MUST point to a
+ location where all of the Configuration Packets needed for the life
+ of the session reside.
+ The port value is specified by the server application bound to the
+ address specified in the c attribute. The bitrate value and channels
+ specified in the rtpmap attribute MUST match the Vorbis sample rate
+ value. An example is found below.
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+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 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
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Vendor string length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Vendor string |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | User comments list length |
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | User comment length / User comment ..
- +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ c=IN IP4/6
+ m=audio RTP/AVP 98
+ a=rtpmap:98 VORBIS/44100/2
+ a=delivery:out_band/http
+ a=fmtp:98 delivery-method:in_band,out_band/http;
+ configuration=base16string1;
+ configuration-uri=http://path/to/the/resource
- Figure 16: Packed Metadata Header
+ Note that the payload format (encoding) names are commonly shown in
+ upper case. MIME subtypes are commonly shown in lower case. These
+ names are case-insensitive in both places. Similarly, parameter
+ names are case-insensitive both in MIME types and in the default
+ mapping to the SDP a=fmtp attribute. The exception regarding case
+ sensitivity is the configuration-uri URI which MUST be regarded as
+ being case sensitive.
- The packed Metadata header also as a slightly different structure to
- that of the RTP payload type with the payload header not being used.
+6.2. Usage with the SDP Offer/Answer Model
-4.2.1 Packed Headers IANA Considerations
+ The answer to any offer, [8], MUST NOT change the URI specified in
+ the configuration-uri attribute. The Configuration inlined in the
+ configuration parameter MAY change.
- The following IANA considerations MUST only be applied to the packed
- headers.
- MIME media type name: audio
+7. Congestion Control
- MIME subtype: vorbis-config
+ Vorbis clients SHOULD send regular receiver reports detailing
+ congestion. A mechanism for dynamically downgrading the stream,
+ known as bitrate peeling, will allow for a graceful backing off of
+ the stream bitrate. This feature is not available at present so an
+ alternative would be to redirect the client to a lower bitrate stream
+ if one is available.
- Required Parameters:
+ If a particular multicast session has a large number of participants
+ care must be taken to prevent an RTCP feedback implosion, [10], in
+ the event of congestion.
- None.
- Optional Parameters:
+8. Examples
- None.
+ The following examples are common usage patterns that MAY be applied
+ in such situations, the main scope of this section is to explain
+ better usage of the transmission vectors.
- Encoding considerations:
+8.1. Stream Radio
- This type is only defined for transfer via HTTP as specified in RFC
- XXXX.
+ That is one of the most common situation: one single server streaming
+ content in multicast, the clients may start a session at random time.
+ The content itself could be a mix of live stream as the dj's speech
- Security Considerations:
- See Section 6 of RFC 3047.
- Interoperability considerations: none
+Barbato Expires April 24, 2006 [Page 19]
+\f
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
- Published specification:
- See RFC XXXX for details.
+ and stored streams as the music she plays.
+ In this situation we don't know in advance how many codebooks we will
+ use. The clients can join anytime and users expect to start
+ listening to the content in a short time
+ On join the client will receive the current Configuration necessary
+ to decode the current stream inlined in the SDP. And can start
+ decoding the current stream.
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-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+ When the streamed content changes the new Configuration is sent in-
+ band before the actual stream, and the Configuration that has to be
+ sent inline in the SDP updated.
+ A serverside optimization would be keep an hash list of the
+ Configurations per session to avoid packing them and send the same
+ Configuration with different Ident tags
- Applications which use this media type:
+ A clientside optimization would be keep a tag list of the
+ Configurations per session and don't process configuration packets
+ already known.
- Vorbis encoded audio, configuration data.
+ Let's assume that the client playout buffer can store at least 7
+ packets.
- Additional information: none
- Person & email address to contact for further information:
+9. Security Considerations
- Phil Kerr: <phil@plus24.com>
+ 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.
- Intended usage: COMMON
- Author/Change controller:
+10. Acknowledgments
- Author: Phil Kerr
+ This document is a continuation of draft-moffitt-vorbis-rtp-00.txt
+ and draft-kerr-avt-vorbis-rtp-04.txt. The MIME type section is a
+ continuation of draft-short-avt-rtp-vorbis-mime-00.txt.
- Change controller: IETF AVT Working Group
+ Thanks to the AVT, Ogg Vorbis Communities / Xiph.org including Steve
+ Casner, Aaron Colwell, Ross Finlayson, Fluendo, Ramon Garcia, Pascal
+ Hennequin, Ralph Giles, Tor-Einar Jarnbjo, Colin Law, John Lazzaro,
+ Jack Moffitt, Christopher Montgomery, Colin Perkins, Barry Short,
+ Mike Smith, Phil Kerr, Michael Sparks, Magnus Westerlund, David
-4.3 Codebook Caching
- Codebook caching allows clients that have previously connected to a
- stream to re-use the associated codebooks and configuration data.
- When a client receives a codebook 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.
-4.4 Loss of Configuration Headers
+Barbato Expires April 24, 2006 [Page 20]
+\f
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
- Unlike the loss of raw Vorbis payload data, loss of a configuration
- 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 Codebook or Setup
- headers MUST result in the halting of stream decoding. Loss of the
- Metadata 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.
+ Barrett, Silvia Pfeiffer, Politecnico di Torino (LS)^3/IMG Group in
+ particular Federico Ridolfo, Francesco Varano, Giampaolo Mancini,
+ Juan Carlos De Martin.
-5. IANA Considerations
- MIME media type name: audio
+11. References
- MIME subtype: vorbis
+11.1. Normative References
- Required Parameters:
+ [1] Pfeiffer, S., "The Ogg Encapsulation Format Version 0",
+ RFC 3533.
- header indicates the URI of the decoding configuration headers.
+ [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 Audio and Video
+ Conferences with Minimal Control.", RFC 3551.
+ [5] Handley, M. and V. Jacobson, "SDP: Session Description
+ Protocol", RFC 2327.
-Kerr Expires August 1, 2005 [Page 20]
+ [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] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
+ Session Description Protocol (SDP)", RFC 3264.
+
+ [9] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
+ RFC 3548.
+
+ [10] 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).
+
+11.2. Informative References
+
+ [11] "libvorbis: Available from the Xiph website,
+ http://www.xiph.org".
+
+ [12] "Ogg Vorbis I specification: Codec setup and packet decode.
+ Available from the Xiph website, http://www.xiph.org".
+
+
+
+Barbato Expires April 24, 2006 [Page 21]
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-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
- Optional Parameters:
+ [13] "Ogg Vorbis I specification: Comment field and header
+ specification. Available from the Xiph website,
+ http://www.xiph.org".
- 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 Vorbis documentation [11] for details.
- Applications which use this media type:
- Audio 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
-5.1 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 ("audio") goes in SDP "m=" as the media name.
- o The MIME subtype ("VORBIS") goes in SDP "a=rtpmap" as the encoding
- name.
-Kerr Expires August 1, 2005 [Page 21]
-\f
- 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 Vorbis files the configuration and
- codebook 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.
- The Vorbis configuration specified in the header attribute MUST
- contain all of the configuration data and codebooks needed for the
- life of the session.
- The port value is specified by the server application bound to the
- address specified in the c attribute. The bitrate value and channels
- specified in the rtpmap attribute MUST match the Vorbis sample rate
- value. An example is found below.
- c=IN IP4/6
- m=audio RTP/AVP 98
- a=rtpmap:98 VORBIS/44100/2
- a=fmtp:98 header=<URL of configuration header>
- Note that the payload format (encoding) names are commonly shown in
- upper case. MIME subtypes are commonly shown in lower case. These
- names are case-insensitive in both places. Similarly, parameter
- names are case-insensitive both in MIME types and in the default
- mapping to the SDP a=fmtp attribute. The exception regarding case
- sensitivity is the configuration header URL which MUST be regarded as
- being case sensitive.
- The answer to any offer, [8], MUST NOT change the URL specified in
- the header attribute.
-6. Congestion Control
- Vorbis clients SHOULD send regular receiver reports detailing
- congestion. A mechanism for dynamically downgrading the stream,
- known as bitrate peeling, will allow for a graceful backing off of
- the stream bitrate. This feature is not available at present so an
- alternative would be to redirect the client to a lower bitrate stream
- if one is available.
- If a particular multicast session has a large number of participants
- care must be taken to prevent an RTCP feedback implosion, [9], in the
- event of congestion.
-Kerr Expires August 1, 2005 [Page 22]
-\f
-Internet-Draft draft-ietf-avt-vorbis-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
- This document is a continuation of draft-moffitt-vorbis-rtp-00.txt.
- The MIME type section is a continuation of
- draft-short-avt-rtp-vorbis-mime-00.txt
- Thanks to the AVT, Ogg Vorbis Communities / Xiph.org including Steve
- Casner, Aaron Colwell, Ross Finlayson, Fluendo, Ramon Garcia, Pascal
- Hennequin, Ralph Giles, Tor-Einar Jarnbjo, Colin Law, John Lazzaro,
- Jack Moffitt, Christopher Montgomery, Colin Perkins, Barry Short,
- Mike Smith, Michael Sparks, Magnus Westerlund.
-9. References
+Barbato Expires April 24, 2006 [Page 22]
+\f
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
-9.1 Normative References
- [1] Pfeiffer, S., "The Ogg Encapsulation Format Version 0", RFC
- 3533.
+Author's Address
- [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
- Levels", RFC 2119.
+ Luca Barbato
+ Xiph.Org
- [3] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
- "RTP: A Transport Protocol for real-time applications", RFC
- 3550.
+ Email: lu_zero@gentoo.org
+ URI: http://www.xiph.org/
- [4] Schulzrinne, H. and S. Casner, "RTP Profile for Audio 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] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
-Kerr Expires August 1, 2005 [Page 23]
-\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
- Session Description Protocol (SDP)", RFC 3264.
- [9] 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).
-9.2 Informative References
- [10] "libvorbis: Available from the Xiph website,
- http://www.xiph.org".
- [11] "Ogg Vorbis I specification: Codec setup and packet decode.
- Available from the Xiph website, http://www.xiph.org".
- [12] "Ogg Vorbis I specification: Comment field and header
- specification. Available from the Xiph website,
- http://www.xiph.org".
- [13] "ITU (1992-1994) ITU-R Recommendation BS. 775-1 Multi-channel
- stereophonic sound system with or without accompanying
- picture. International Telecommunications Union. Available
- from the ITU website, http://www.itu.int".
-Author's Address
- Phil Kerr
- Xiph.Org
- EMail: phil@plus24.com
- URI: http://www.xiph.org/
-Kerr Expires August 1, 2005 [Page 24]
+
+
+
+
+
+Barbato Expires April 24, 2006 [Page 23]
\f
-Internet-Draft draft-ietf-avt-vorbis-rtp-00 January 2005
+Internet-Draft draft-kerr-avt-vorbis-rtp-05 October 2005
Intellectual Property Statement
-Kerr Expires August 1, 2005 [Page 25]
+Barbato Expires April 24, 2006 [Page 24]
\f
+
projects / platform / upstream / libvorbis.git / commitdiff