< draft-ietf-avt-rtp-vorbis-08.txt   draft-ietf-avt-rtp-vorbis-09.txt >
AVT Working Group L. Barbato AVT Working Group L. Barbato
Internet-Draft Xiph.Org Internet-Draft Xiph
Expires: May 20, 2008 Nov 17, 2007 Expires: August 20, 2008 Feb 17, 2008
draft-ietf-avt-rtp-vorbis-08
RTP Payload Format for Vorbis Encoded Audio RTP Payload Format for Vorbis Encoded Audio
draft-ietf-avt-rtp-vorbis-09
Status of this Memo Status of This Memo
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skipping to change at page 1, line 33 skipping to change at page 1, line 33
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Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
Abstract Abstract
This document describes an RTP payload format for transporting Vorbis This document describes an RTP payload format for transporting Vorbis
encoded audio. It details the RTP encapsulation mechanism for raw encoded audio. It details the RTP encapsulation mechanism for raw
Vorbis data and details the delivery mechanisms for the decoder Vorbis data and details the delivery mechanisms for the decoder
probability model, referred to as a codebook and other setup probability model, referred to as a codebook and other setup
information. information.
Also included within this memo are media type registrations, and the Also included within this memo are media type registrations, and the
skipping to change at page 2, line 13 skipping to change at page 2, line 13
Protocol (SDP). Protocol (SDP).
Editors Note Editors Note
All references to RFC XXXX are to be replaced by references to the All references to RFC XXXX are to be replaced by references to the
RFC number of this memo, when published. RFC number of this memo, when published.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conformance and Document Conventions . . . . . . . . . . . 3
2. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Example RTP Packet . . . . . . . . . . . . . . . . . . . . 7 2.4. Example RTP Packet . . . . . . . . . . . . . . . . . . . . 7
3. Configuration Headers . . . . . . . . . . . . . . . . . . . . 8 3. Configuration Headers . . . . . . . . . . . . . . . . . . . . 8
3.1. In-band Header Transmission . . . . . . . . . . . . . . . 9 3.1. In-band Header Transmission . . . . . . . . . . . . . . . 9
3.1.1. Packed Configuration . . . . . . . . . . . . . . . . . 9 3.1.1. Packed Configuration . . . . . . . . . . . . . . . . . 9
3.2. Out of Band Transmission . . . . . . . . . . . . . . . . . 11 3.2. Out of Band Transmission . . . . . . . . . . . . . . . . . 11
3.2.1. Packed Headers . . . . . . . . . . . . . . . . . . . . 11 3.2.1. Packed Headers . . . . . . . . . . . . . . . . . . . . 11
3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 12 3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 12
4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 12 4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 12
5. Frame Packetization . . . . . . . . . . . . . . . . . . . . . 13 5. Frame Packetization . . . . . . . . . . . . . . . . . . . . . 13
5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 14 5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 14
5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 16 5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
6.1. Packed Headers IANA Considerations . . . . . . . . . . . . 18 6.1. Packed Headers IANA Considerations . . . . . . . . . . . . 18
7. SDP related considerations . . . . . . . . . . . . . . . . . . 20 7. SDP related considerations . . . . . . . . . . . . . . . . . . 19
7.1. Mapping Media Type Parameters into SDP . . . . . . . . . . 20 7.1. Mapping Media Type Parameters into SDP . . . . . . . . . . 20
7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 21 7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 20
7.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 21 7.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 21
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 22 9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22 9.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 11. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . . 23 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . . 24 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 24 13.1. Normative References . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . . . 25 13.2. Informative References . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
Vorbis is a general purpose perceptual audio codec intended to allow Vorbis is a general purpose perceptual audio codec intended to allow
maximum encoder flexibility, thus allowing it to scale competitively maximum encoder flexibility, thus allowing it to scale competitively
over an exceptionally wide range of bitrates. At the high quality/ 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 bitrate end of the scale (CD or DAT rate stereo, 16/24 bits), it is
in the same league as MPEG-4 AAC. Vorbis is also intended for lower in the same league as MPEG-4 AAC. Vorbis is also intended for lower
and higher sample rates (from 8kHz telephony to 192kHz digital and higher sample rates (from 8kHz telephony to 192kHz digital
masters) and a range of channel representations (monaural, masters) and a range of channel representations (monaural,
polyphonic, stereo, quadraphonic, 5.1, ambisonic, or up to 255 polyphonic, stereo, quadraphonic, 5.1, ambisonic, or up to 255
discrete channels). discrete channels).
Vorbis encoded audio is generally encapsulated within an Ogg format Vorbis encoded audio is generally encapsulated within an Ogg format
bitstream [11], which provides framing and synchronization. For the bitstream [11], which provides framing and synchronization. For the
purposes of RTP transport, this layer is unnecessary, and so raw purposes of RTP transport, this layer is unnecessary, and so raw
Vorbis packets are used in the payload. Vorbis packets are used in the payload.
1.1. Terminology 1.1. Conformance and Document Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1]. document are to be interpreted as described in BCP 14, [1] and
indicate requirement levels for compliant implementations.
Requirements apply to all implementations unless otherwise stated.
An implementation is a software module that supports one of the media
types defined in this document. Software modules may support
multiple media types, but conformance is considered individually for
each type.
Implementations that fail to satisfy one or more "MUST" requirements
are considered non-compliant. Implementations that satisfy all
"MUST" requirements, but fail to satisfy one or more "SHOULD"
requirements, are said to be "conditionally compliant". All other
implementations are "unconditionally compliant".
2. Payload Format 2. Payload Format
For RTP based transport of Vorbis encoded audio the standard RTP For RTP based transport of Vorbis encoded audio the standard RTP
header is followed by a 4 octets payload header, then the payload header is followed by a 4 octets payload header, then the payload
data. The payload headers are used to associate the Vorbis data with data. The payload headers are used to associate the Vorbis data with
its associated decoding codebooks as well as indicating if the its associated decoding codebooks as well as indicating if the
following packet contains fragmented Vorbis data and/or the number of following packet contains fragmented Vorbis data and/or the number of
whole Vorbis data frames. The payload data contains the raw Vorbis whole Vorbis data frames. The payload data contains the raw Vorbis
bitstream information. There are 3 types of Vorbis data, an RTP bitstream information. There are 3 types of Vorbis data, an RTP
skipping to change at page 8, line 29 skipping to change at page 8, line 36
comment header packet which gives simple metadata about the stream, comment header packet which gives simple metadata about the stream,
but this information is not required for decoding the frame sequence. but this information is not required for decoding the frame sequence.
Thus these two codebook header packets must be received by the Thus these two codebook header packets must be received by the
decoder before any audio data can be interpreted. These requirements decoder before any audio data can be interpreted. These requirements
pose problems in RTP, which is often used over unreliable transports. pose problems in RTP, which is often used over unreliable transports.
Since this information must be transmitted reliably and, as the RTP Since this information must be transmitted reliably and, as the RTP
stream may change certain configuration data mid-session, there are stream may change certain configuration data mid-session, there are
different methods for delivering this configuration data to a client, different methods for delivering this configuration data to a client,
both in-band and out-of-band which is detailed below. SDP delivery both in-band and out-of-band which is detailed below. In order to
is typically used to set up an initial state for the client set up an initial state for the client application the configuration
application. The changes may be due to different codebooks as well MUST be conveyed via the signalling channel used to setup the
as different bitrates of the stream. session. One example of such signalling is SDP [5] with the Offer/
Answer Model [8]. Changes to the configuration MAY be communicated
via a re-invite, conveying new SDP, or sent in-band in the RTP
channel. Implementations MUST support in-band delivery of updated
codebooks, and SHOULD support out-of-band codebook update using a new
SDP file. The changes may be due to different codebooks as well as
different bitrates of the RTP stream.
The delivery vectors in use can be specified by an SDP attribute to For non chained streams, the recommended Configuration delivery
indicate the method and the optional URI where the Vorbis Packed method is inline the Packed Configuration (Section 3.1.1) in the SDP
Configuration (Section 3.1.1) Packets could be fetched. Different as explained in the IANA considerations (Section 7.1).
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 recommended Configuration
delivery method is inline the Packed Configuration (Section 3.1.1) in
the SDP as explained in the IANA considerations (Section 7.1).
The 24 bit Ident field is used to map which Configuration will be The 24 bit Ident field is used to map which Configuration will be
used to decode a packet. When the Ident field changes, it indicates used to decode a packet. When the Ident field changes, it indicates
that a change in the stream has taken place. The client application that a change in the stream has taken place. The client application
MUST have in advance the correct configuration and if the client MUST have in advance the correct configuration and if the client
detects a change in the Ident value and does not have this detects a change in the Ident value and does not have this
information it MUST NOT decode the raw Vorbis data associated until information it MUST NOT decode the raw Vorbis data associated until
it fetches the correct Configuration. it fetches the correct Configuration.
3.1. In-band Header Transmission 3.1. In-band Header Transmission
The Packed Configuration (Section 3.1.1) Payload is sent in-band with The Packed Configuration (Section 3.1.1) Payload is sent in-band with
the packet type bits set to match the Vorbis Data Type. Clients MUST the packet type bits set to match the Vorbis Data Type. Clients MUST
be capable of dealing with fragmentation and periodic re-transmission be capable of dealing with fragmentation and periodic re-transmission
of [14] the configuration headers. The RTP timestamp value MUST of [14] the configuration headers. The RTP timestamp value MUST
reflect the transmission time of the next data packet. reflect the transmission time of the first data packet for which this
configuration applies.
3.1.1. Packed Configuration 3.1.1. Packed Configuration
A Vorbis Packed Configuration is indicated with the Vorbis Data Type A Vorbis Packed Configuration is indicated with the Vorbis Data Type
field set to 1. Of the three headers defined in the Vorbis I field set to 1. Of the three headers defined in the Vorbis I
specification [10], the Identification and the Setup MUST be packed specification [10], the Identification and the Setup MUST be packed
as they are, while the comment header MAY be replaced with a dummy as they are, while the comment header MAY be replaced with a dummy
one. The packed configuration follows a generic way to store xiph one.
codec configurations: The first field stores the number of the
following packets minus one (count field), the next ones represent The packed configuration follows a generic way to store Xiph codec
the size of the headers (length fields), the headers immediately configurations: The first field stores the number of the following
follow the list of length fields. The size of the last header is packets minus one (count field), the next ones represent the size of
implicit. The count and the length fields are encoded using the the headers (length fields), the headers immediately follow the list
following logic: the data is in network byte order, every byte has of length fields. The size of the last header is implicit.
the most significant bit used as flag and the following 7 used to
store the value. The first N bit are to be taken, where N is number The count and the length fields are encoded using the following
of bits needed to represent the value, taken modulo 7, and stored in logic: the data is in network byte order, every byte has the most
the first byte. If there are more bits, the flag bit is set to 1 and significant bit used as flag and the following 7 used to store the
the subsequent 7bit are stored in the following byte, if there are value. The first N bit are to be taken, where N is number of bits
needed to represent the value, taken modulo 7, and stored in the
first byte. If there are more bits, the flag bit is set to 1 and the
subsequent 7bit are stored in the following byte, if there are
remaining bits set the flag to 1 and the same procedure is repeated. remaining bits set the flag to 1 and the same procedure is repeated.
The ending byte has the flag bit set to 0. In order to decode it is The ending byte has the flag bit set to 0. In order to decode it is
enough to iterate over the bytes until the flag bit set to 0, for enough to iterate over the bytes until the flag bit set to 0, for
every byte the data is added to the accumulated value multiplied by every byte the data is added to the accumulated value multiplied by
128. The headers are packed in the same order they are present in 128.
ogg: Identification, Comment, Setup.
The headers are packed in the same order they are present in ogg:
Identification, Comment, Setup.
The 2 byte length tag defines the length of the packed headers as the
sum of the Configuration, Comment and Setup lengths.
0 1 2 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 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 | xxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| xxxxx | | xxxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier | | synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
skipping to change at page 11, line 7 skipping to change at page 11, line 7
Figure 5: Packed Configuration Figure Figure 5: Packed Configuration Figure
The Ident field is set with the value that will be used by the Raw 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 Payload Packets to address this Configuration. The Fragment type is
set to 0 since the packet bears the full Packed configuration, the set to 0 since the packet bears the full Packed configuration, the
number of packet is set to 1. number of packet is set to 1.
3.2. Out of Band Transmission 3.2. Out of Band Transmission
This section, as stated above, does not cover all the possible out- The following packet definition MUST be used when Configuration is
of-band delivery methods since they rely on different protocols and inlined in the SDP.
are linked to specific applications. 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 3.2.1. Packed Headers
As mentioned above the RECOMMENDED delivery vector for Vorbis As mentioned above the RECOMMENDED delivery vector for Vorbis
configuration data is via a retrieval method that can be performed configuration data is via a retrieval method that can be performed
using a reliable transport protocol. As the RTP headers are not using a reliable transport protocol. As the RTP headers are not
required for this method of delivery the structure of the required for this method of delivery the structure of the
configuration data is slightly different. The packed header starts configuration data is slightly different. The packed header starts
with a 32 bit (network byte ordered) count field which details the with a 32 bit (network byte ordered) count field which details the
number of packed headers that are contained in the bundle. Next is number of packed headers that are contained in the bundle. Next is
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packed header | | Packed header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packed header | | Packed header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Packed Headers Overview Figure 6: 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.
0 1 2 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ident | length .. | Ident | length ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. | n. of headers | length1 | length2 .. .. | n. of headers | length1 | length2 ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. | Identification Header .. .. | Identification Header ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
................................................................. .................................................................
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The key difference between the in-band format and this one, is that The key difference between the in-band format and this one, is that
there is no need for the payload header octet. In this figure the there is no need for the payload header octet. In this figure the
comment has a size bigger than 127 bytes. comment has a size bigger than 127 bytes.
3.3. Loss of Configuration Headers 3.3. Loss of Configuration Headers
Unlike the loss of raw Vorbis payload data, loss of a configuration Unlike the loss of raw Vorbis payload data, loss of a configuration
header lead to a situation where it will not be possible to header lead to a situation where it will not be possible to
successfully decode the stream. Implementations MAY try to recover successfully decode the stream. Implementations MAY try to recover
from error requesting again the missing Configuration, the baseline from error by requesting again the missing Configuration or, if the
reaction SHOULD be either reset or end the connection. delivery method is in-band, by buffering the payloads waiting for the
Configuration needed to decode them. The baseline reaction SHOULD be
either reset or end the RTP session.
4. Comment Headers 4. Comment Headers
With the Vorbis Data Type flag set to 2, this indicates that the With the Vorbis Data Type flag set to 2, this indicates that the
packet contain the comment metadata, such as artist name, track title packet contain the comment metadata, such as artist name, track title
and so on. These metadata messages are not intended to be fully and so on. These metadata messages are not intended to be fully
descriptive but to offer basic track/song information. Clients MAY descriptive but to offer basic track/song information. Clients MAY
ignore it completely. The details on the format of the comments can ignore it completely. The details on the format of the comments can
be found in the Vorbis documentation [10]. be found in the Vorbis documentation [10].
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Required parameters: Required parameters:
rate: indicates the RTP timestamp clock rate as described in RTP rate: indicates the RTP timestamp clock rate as described in RTP
Profile for Audio and Video Conferences with Minimal Control. Profile for Audio and Video Conferences with Minimal Control.
[3] [3]
channels: indicates the number of audio channels as described in channels: indicates the number of audio channels as described in
RTP Profile for Audio and Video Conferences with Minimal RTP Profile for Audio and Video Conferences with Minimal
Control. [3] Control. [3]
delivery-method: indicates the delivery methods in use, the
possible values are: inline, in_band, out_band. The parameter
MAY be included multiple time, followed by the configuration or
configuration-uri parameter associated.
configuration: the base64 [9] representation of the Packed configuration: the base64 [9] representation of the Packed
Headers (Section 3.2.1). It MUST follow the associated Headers (Section 3.2.1).
delivery-method parameter ("inline").
Optional parameters:
configuration-uri: the URI [4] of the configuration headers in
case of out of band transmission. In the form of
"scheme://path/to/resource/", depending on the specific method,
a single configuration packet could be retrived by its Ident
number, or multiple packets could be aggregated in a single
stream. Non hierarchical protocols MAY point to a resource
using their specific syntax.
Encoding considerations: Encoding considerations:
This media type is framed and contains binary data. This media type is framed and contains binary data.
Security considerations: Security considerations:
See Section 10 of RFC XXXX. See Section 10 of RFC XXXX.
Interoperability considerations: Interoperability considerations:
None None
Published specification: Published specification:
RFC XXXX [RFC Editor: please replace by the RFC number of this RFC XXXX [RFC Editor: please replace by the RFC number of this
memo, when published] memo, when published]
Ogg Vorbis I specification: Codec setup and packet decode. Ogg Vorbis I specification: Codec setup and packet decode.
Available from the Xiph website, http://www.xiph.org Available from the Xiph website, http://xiph.org
Applications which use this media type: Applications which use this media type:
Audio streaming and conferencing tools Audio streaming and conferencing tools
Additional information: Additional information:
None None
Person & email address to contact for further information: Person & email address to contact for further information:
skipping to change at page 18, line 45 skipping to change at page 18, line 29
Author: Author:
Luca Barbato Luca Barbato
Change controller: Change controller:
IETF AVT Working Group delegated from the IESG IETF AVT Working Group delegated from the IESG
6.1. Packed Headers IANA Considerations 6.1. Packed Headers IANA Considerations
The following IANA considerations MUST only be applied to the Packed The following IANA considerations refers to the split configuration
Headers (Section 3.2.1). Packed Headers (Section 3.2.1) used within RFC XXXX.
Type name: audio Type name: audio
Subtype name: vorbis-config Subtype name: vorbis-config
Required parameters: Required parameters:
None None
Optional parameters: Optional parameters:
skipping to change at page 20, line 4 skipping to change at page 19, line 32
Additional information: Additional information:
None None
Person & email address to contact for further information: Person & email address to contact for further information:
Luca Barbato: <lu_zero@gentoo.org> Luca Barbato: <lu_zero@gentoo.org>
IETF Audio/Video Transport Working Group IETF Audio/Video Transport Working Group
Intended usage: COMMON Intended usage: COMMON
Restriction on usage: Restriction on usage:
This media type doesn't depend on the transport. This media type doesn't depend on the transport.
Author: Author:
Luca Barbato Luca Barbato
Change controller: Change controller:
IETF AVT Working Group delegated from the IESG IETF AVT Working Group delegated from the IESG
7. SDP related considerations 7. SDP related considerations
The following paragraphs define the mapping of the parameters The following paragraphs define the mapping of the parameters
described in the IANA considerations section and their usage in the described in the IANA considerations section and their usage in the
Offer/Answer Model [8]. Offer/Answer Model [8]. In order to be forward compatible the
implementation MUST ignore unknown parameters.
7.1. Mapping Media Type Parameters into SDP 7.1. Mapping Media Type Parameters into SDP
The information carried in the Media Type specification has a The information carried in the Media Type specification has a
specific mapping to fields in the Session Description Protocol (SDP) specific mapping to fields in the Session Description Protocol (SDP)
[5], which is commonly used to describe RTP sessions. When SDP is [5], which is commonly used to describe RTP sessions. When SDP is
used to specify sessions the mapping are as follows: used to specify sessions the mapping are as follows:
o The type name ("audio") goes in SDP "m=" as the media name. o The type name ("audio") goes in SDP "m=" as the media name.
o The subtype name ("vorbis") goes in SDP "a=rtpmap" as the encoding o The subtype name ("vorbis") goes in SDP "a=rtpmap" as the encoding
name. name.
o The parameter "rate" also goes in "a=rtpmap" as clock rate. 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 "channels" also goes in "a=rtpmap" as channel count.
o The mandated parameters "delivery-method" and "configuration" MUST o The mandated parameters "configuration" MUST be included in the
be included in the SDP "a=fmtp" attribute. SDP "a=fmtp" attribute.
o The optional parameter "configuration-uri", when present, MUST be
included in the SDP "a=fmtp" attribute and MUST follow the
delivery-method that applies.
If the stream comprises chained Vorbis files and all of them are If the stream comprises chained Vorbis files and all of them are
known in advance, the Configuration Packet for each file SHOULD be known in advance, the Configuration Packet for each file SHOULD be
passed to the client using the configuration attribute. 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 The port value is specified by the server application bound to the
address specified in the c= line. The bitrate value and channels address specified in the c= line. The channel count value specified
specified in the rtpmap attribute MUST match the Vorbis sample rate in the rtpmap attribute SHOULD match the current Vorbis stream or
value. An example is found below. considered the maximum number of channels to be expected. The
timestamp clock rate MUST be a multiple of the sample rate, different
payload number MUST be used if the clock rate changes. The
Configuration payload delivers the exact information, thus the SDP
information SHOULD be considered as a hint. An example is found
below.
7.1.1. SDP Example 7.1.1. SDP Example
The following example shows a basic SDP single stream. The first The following example shows a basic SDP single stream. The first
configuration packet is inlined in the SDP, other configurations configuration packet is inlined in the SDP, other configurations
could be fetched at any time from the URIs provided. The inline could be fetched at any time from the URIs provided. The inline
base64 [9] configuration string is folded in this example due to RFC base64 [9] configuration string is folded in this example due to RFC
line length limitations. line length limitations.
c=IN IP4 192.0.2.1 c=IN IP4 192.0.2.1
m=audio RTP/AVP 98 m=audio RTP/AVP 98
a=rtpmap:98 vorbis/44100/2 a=rtpmap:98 vorbis/44100/2
a=fmtp:98 delivery-method=inline; a=fmtp:98 configuration=AAAAAZ2f4g9NAh4aAXZvcmJpcwA...;
configuration=AAAAAZ2f4g9NAh4aAXZvcmJpcwA...; delivery-
method=out_band; configuration-uri=rtsp://path/to/the/resource;
delivery-method=out_band;
configuration-uri=http://another/path/to/resource/;
Note that the payload format (encoding) names are commonly shown in Note that the payload format (encoding) names are commonly shown in
upper case. Media Type subtypes are commonly shown in lower case. upper case. Media Type subtypes are commonly shown in lower case.
These names are case-insensitive in both places. Similarly, These names are case-insensitive in both places. Similarly,
parameter names are case-insensitive both in Media Type types and in parameter names are case-insensitive both in Media Type types and in
the default mapping to the SDP a=fmtp attribute. The exception the default mapping to the SDP a=fmtp attribute. The a=fmtp line is
regarding case sensitivity is the configuration-uri URI which MUST be a single line even if it is shown as multiple lines in this document
regarded as being case sensitive. The a=fmtp line is a single line for clarity.
even if it is shown as multiple lines in this document for clarity.
7.2. Usage with the SDP Offer/Answer Model 7.2. Usage with the SDP Offer/Answer Model
The only parameter negotiable is the delivery method. All the others The are no negotiable parameters. All the of them are declarative.
are declarative: the offer, as described in An Offer/Answer Model
Session Description Protocol [8], may contain a large number of
delivery methods per single fmtp attribute, the answerer MUST remove
every delivery-method and configuration-uri not supported. All the
parameters MUST not be altered on answer otherwise.
8. Examples 8. Congestion Control
The following examples are common usage patterns that MAY be applied The general congestion control considerations for transporting RTP
in such situations, the main scope of this section is to explain data apply to vorbis audio over RTP as well. See the RTP
better usage of the transmission vectors. specification [2] and any applicable RTP profile (e.g., [3]). Audio
data can be encoded using a range of different bit rates, so it is
possible to adapt network bandwidth by adjusting the encoder bit rate
in real time or by having multiple copies of content encoded at
different bit rates.
8.1. Stream Radio 9. Example
The following example shows a common usage pattern that MAY be
applied in such situation, the main scope of this section is to
explain better usage of the transmission vectors.
9.1. Stream Radio
This is one of the most common situation: one single server streaming This is one of the most common situation: one single server streaming
content in multicast, the clients may start a session at random time. content in multicast, the clients may start a session at random time.
The content itself could be a mix of live stream, as the webjockey's The content itself could be a mix of live stream, as the webjockey's
voice, and stored streams as the music she plays. voice, and stored streams as the music she plays.
In this situation we don't know in advance how many codebooks we will 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 use. The clients can join anytime and users expect to start
listening to the content in a short time. listening to the content in a short time.
On join the client will receive the current Configuration necessary On join the client will receive the current Configuration necessary
to decode the current stream inlined in the SDP so that the decoding to decode the current stream inlined in the SDP so that the decoding
will start immediately after. will start immediately after.
When the streamed content changes the new Configuration is sent in- When the streamed content changes the new Configuration is sent in-
band before the actual stream and the Configuration that has to be band before the actual stream and the Configuration that has to be
sent inline in the SDP updated. Since the in-band method is sent inline in the SDP updated. Since the in-band method is
unreliable, an out of band fallback is provided. unreliable, an out of band fallback is provided.
The client MAY choose to fetch the Configuration from the alternate The client may choose to fetch the Configuration from the alternate
source as soon as it discovers a Configuration packet got lost in- source as soon as it discovers a Configuration packet got lost in-
band or use selective retransmission [13], if the server supports the band or use selective retransmission [13], if the server supports the
feature. feature.
A serverside optimization would be to keep an hash list of the A serverside optimization would be to keep an hash list of the
Configurations per session to avoid packing all of them and send the Configurations per session to avoid packing all of them and send the
same Configuration with different Ident tags same Configuration with different Ident tags
A clientside optimization would be to keep a tag list of the A clientside optimization would be to keep a tag list of the
Configurations per session and don't process configuration packets Configurations per session and don't process configuration packets
already known. already known.
9. Security Considerations 10. Security Considerations
RTP packets using this payload format are subject to the security RTP packets using this payload format are subject to the security
considerations discussed in the RTP specification [2], the base64 considerations discussed in the RTP specification [2], the base64
specification [9] and the URI Generic syntax specification [4]. specification [9] and the URI Generic syntax specification [4].
Among other considerations, this implies that the confidentiality of Among other considerations, this implies that the confidentiality of
the media stream is archieved by using encryption. Because the data the media stream is archieved by using encryption. Because the data
compression used with this payload format is applied end-to-end, compression used with this payload format is applied end-to-end,
encryption may be performed on the compressed data. Additional care encryption may be performed on the compressed data.
MAY be needed for delivery methods that point to external resources,
using secure protocols to fetch the configuration payloads. Where
the size of a data block is set, care MUST be taken to prevent buffer
overflows in the client applications.
10. Acknowledgments 11. Copying Conditions
The authors agree to grant third parties the irrevocable right to
copy, use and distribute the work, with or without modification, in
any medium, without royalty, provided that, unless separate
permission is granted, redistributed modified works do not contain
misleading author, version, name of work, or endorsement information.
12. Acknowledgments
This document is a continuation of draft-moffitt-vorbis-rtp-00.txt This document is a continuation of draft-moffitt-vorbis-rtp-00.txt
and draft-kerr-avt-vorbis-rtp-04.txt. The Media Type declaration is and draft-kerr-avt-vorbis-rtp-04.txt. The Media Type declaration is
a continuation of draft-short-avt-rtp-vorbis-mime-00.txt. a continuation of draft-short-avt-rtp-vorbis-mime-00.txt.
Thanks to the AVT, Ogg Vorbis Communities / Xiph.org including Steve Thanks to the AVT, Vorbis Communities / Xiph.Org Foundation including
Casner, Aaron Colwell, Ross Finlayson, Fluendo, Ramon Garcia, Pascal Steve Casner, Aaron Colwell, Ross Finlayson, Fluendo, Ramon Garcia,
Hennequin, Ralph Giles, Tor-Einar Jarnbjo, Colin Law, John Lazzaro, Pascal Hennequin, Ralph Giles, Tor-Einar Jarnbjo, Colin Law, John
Jack Moffitt, Christopher Montgomery, Colin Perkins, Barry Short, Lazzaro, Jack Moffitt, Christopher Montgomery, Colin Perkins, Barry
Mike Smith, Phil Kerr, Michael Sparks, Magnus Westerlund, David Short, Mike Smith, Phil Kerr, Michael Sparks, Magnus Westerlund,
Barrett, Silvia Pfeiffer, Stefan Ehmann, Alessandro Salvatori. David Barrett, Silvia Pfeiffer, Stefan Ehmann, Alessandro Salvatori.
Politecnico di Torino (LS)^3/IMG Group in particular Federico Politecnico di Torino (LS)^3/IMG Group in particular Federico
Ridolfo, Francesco Varano, Giampaolo Mancini, Dario Gallucci, Juan Ridolfo, Francesco Varano, Giampaolo Mancini, Dario Gallucci, Juan
Carlos De Martin. Carlos De Martin.
11. References 13. References
13.1. Normative References
11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119. Levels", RFC 2119.
[2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, [2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for real-time applications", STD 64, "RTP: A Transport Protocol for real-time applications", STD 64,
RFC 3550. RFC 3550.
[3] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video [3] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control.", STD 65, RFC 3551. Conferences with Minimal Control.", STD 65, RFC 3551.
skipping to change at page 24, line 9 skipping to change at page 23, line 38
[8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with [8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264. Session Description Protocol (SDP)", RFC 3264.
[9] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", [9] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 3548. RFC 3548.
[10] "Ogg Vorbis I specification: Codec setup and packet decode. [10] "Ogg Vorbis I specification: Codec setup and packet decode.
Available from the Xiph website, Available from the Xiph website,
http://xiph.org/vorbis/doc/Vorbis_I_spec.html". http://xiph.org/vorbis/doc/Vorbis_I_spec.html".
11.2. Informative References 13.2. Informative References
[11] Pfeiffer, S., "The Ogg Encapsulation Format Version 0", [11] Pfeiffer, S., "The Ogg Encapsulation Format Version 0",
RFC 3533. RFC 3533.
[12] "libvorbis: Available from the dedicated website, [12] "libvorbis: Available from the dedicated website,
http://www.vorbis.com". http://vorbis.com".
[13] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol [13] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol
Extended Reports (RTCP XR)", RFC 3611, November 2003. Extended Reports (RTCP XR)", RFC 3611, November 2003.
[14] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, [14] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg,
"RTP Retransmission Payload Format", RFC 4588, July 2006. "RTP Retransmission Payload Format", RFC 4588, July 2006.
Author's Address Author's Address
Luca Barbato Luca Barbato
Xiph.Org Xiph.Org Foundation
Email: lu_zero@gentoo.org EMail: lu_zero@gentoo.org
URI: http://www.xiph.org/ URI: http://xiph.org/
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
skipping to change at page 25, line 45 skipping to change at page 25, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment Acknowledgement
Funding for the RFC Editor function is provided by the IETF Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA). Administrative Support Activity (IASA).
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