AVT Working Group L. Barbato
Internet-Draft Xiph
-Expires: July 8, 2008 Jan 05, 2008
+Expires: July 17, 2008 Jan 14, 2008
RTP Payload Format for Vorbis Encoded Audio
- draft-ietf-avt-rtp-vorbis-08
+ draft-ietf-avt-rtp-vorbis-09
Status of This Memo
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
- This Internet-Draft will expire on July 8, 2008.
+ This Internet-Draft will expire on July 17, 2008.
Copyright Notice
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5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
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
- 7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 21
+ 7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 20
7.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 21
- 8. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
- 8.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 22
- 9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
- 10. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 23
- 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
- 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
- 12.1. Normative References . . . . . . . . . . . . . . . . . . . 23
- 12.2. Informative References . . . . . . . . . . . . . . . . . . 24
+ 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 21
+ 9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
+ 9.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 21
+ 10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
+ 11. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 22
+ 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
+ 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
+ 13.1. Normative References . . . . . . . . . . . . . . . . . . . 22
+ 13.2. Informative References . . . . . . . . . . . . . . . . . . 23
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application. 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
- 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 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).
+ 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
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used to decode a 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
information it MUST NOT decode the raw Vorbis data associated until
it fetches the correct Configuration.
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3.1. In-band Header Transmission
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
be capable of dealing with fragmentation and periodic re-transmission
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
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3.2. Out of Band Transmission
- This section, as stated above, does not cover all the possible out-
- of-band delivery methods since they rely on different protocols and
- 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.
+ The following packet definition MUST be used when Configuration is
+ inlined in the SDP.
3.2.1. Packed Headers
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RTP Profile for Audio and Video Conferences with Minimal
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
- Headers (Section 3.2.1). It MUST follow the associated
- 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.
+ Headers (Section 3.2.1).
Encoding considerations:
None
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Published specification:
RFC XXXX [RFC Editor: please replace by the RFC number of this
None
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Person & email address to contact for further information:
Luca Barbato: <lu_zero@gentoo.org> IETF Audio/Video Transport
6.1. Packed Headers IANA Considerations
- The following IANA considerations MUST only be applied to the Packed
- Headers (Section 3.2.1).
+ The following IANA considerations refers to the split configuration
+ Packed Headers (Section 3.2.1) used within RFC XXXX.
+ Type name: audio
+ Subtype name: vorbis-config
+ Required parameters:
+ None
+ Optional parameters:
+ None
+ Encoding considerations:
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+ This media type contains binary data.
- Type name: audio
- Subtype name: vorbis-config
- Required parameters:
- None
- Optional parameters:
- None
- Encoding considerations:
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- This media type contains binary data.
Security considerations:
Intended usage: COMMON
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Restriction on usage:
This media type doesn't depend on the transport.
The following paragraphs define the mapping of the parameters
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.
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7.1. Mapping Media Type Parameters into SDP
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=fmtp" attribute.
+ o The mandated parameters "configuration" MUST be included in the
+ 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
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.
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The port value is specified by the server application bound to the
address specified in the c= line. The sample rate and channel count
value specified in the rtpmap attribute SHOULD match the current
Vorbis stream or considered the maximum number of channels to be
- expected and the least common multiple for the session. The
- Configuration payload delivers the exact information, thus the SDP
- information SHOULD be considered as a hint. An example is found
+ expected and the least common multiple sample rate for the session.
+ 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
c=IN IP4 192.0.2.1
m=audio RTP/AVP 98
a=rtpmap:98 vorbis/44100/2
- a=fmtp:98 delivery-method=inline;
- configuration=AAAAAZ2f4g9NAh4aAXZvcmJpcwA...; delivery-
- method=out_band; configuration-uri=rtsp://path/to/the/resource;
- delivery-method=out_band;
- configuration-uri=http://another/path/to/resource/;
+ a=fmtp:98 configuration=AAAAAZ2f4g9NAh4aAXZvcmJpcwA...;
Note that the payload format (encoding) names are commonly shown in
upper case. Media Type subtypes are commonly shown in lower case.
These names are case-insensitive in both places. Similarly,
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parameter names are case-insensitive both in Media Type 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 a=fmtp line is a single line
- even if it is shown as multiple lines in this document for clarity.
+ the default mapping to the SDP a=fmtp attribute. The a=fmtp line is
+ a single line even if it is shown as multiple lines in this document
+ for clarity.
7.2. Usage with the SDP Offer/Answer Model
- The only parameter negotiable is the delivery method. All the others
- 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.
+ The are no negotiable parameters. All the of them are declarative.
+
+8. Congestion Control
-8. Example
+ Vorbis clients SHOULD send regular receiver reports detailing
+ congestion. A way to handle bandwidth changes MAY be redirect the
+ client to a lower bitrate stream if one is available.
+
+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.
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-8.1. Stream Radio
+9.1. Stream Radio
This is one of the most common situation: one single server streaming
content in multicast, the clients may start a session at random time.
A serverside optimization would be to keep an hash list of the
Configurations per session to avoid packing all of them and send the
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same Configuration with different Ident tags
A clientside optimization would be to keep a tag list of the
Configurations per session and don't process configuration packets
already known.
-9. Security Considerations
+10. Security Considerations
RTP packets using this payload format are subject to the security
considerations discussed in the RTP specification [2], the base64
Among other considerations, this implies that the confidentiality of
the media stream is archieved 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. Additional care
- 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.
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+ encryption may be performed on the compressed data.
-10. Copying Conditions
+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
permission is granted, redistributed modified works do not contain
misleading author, version, name of work, or endorsement information.
-11. Acknowledgments
+12. Acknowledgments
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
Ridolfo, Francesco Varano, Giampaolo Mancini, Dario Gallucci, Juan
Carlos De Martin.
-12. References
+13. References
-12.1. Normative References
+13.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119.
[2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
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"RTP: A Transport Protocol for real-time applications", STD 64,
RFC 3550.
November 1990.
[7] McCann et al., J., "Path MTU Discovery for IP version 6",
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RFC 1981.
[8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Available from the Xiph website,
http://xiph.org/vorbis/doc/Vorbis_I_spec.html".
-12.2. Informative References
+13.2. Informative References
[11] Pfeiffer, S., "The Ogg Encapsulation Format Version 0",
RFC 3533.
[14] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg,
"RTP Retransmission Payload Format", RFC 4588, July 2006.
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Author's Address
Luca Barbato
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