Network Working Group Phil Kerr
Internet-Draft Ogg Vorbis Community
-June 10, 2003 OpenDrama
-Expires: December 10, 2003
+October 27, 2003 OpenDrama
+Expires: April 27, 2003
RTP Payload Format for Vorbis Encoded Audio
- <draft-kerr-avt-vorbis-rtp-02.txt>
+ <draft-kerr-avt-vorbis-rtp-03.txt>
Status of this Memo
decoder probability model, referred to as a codebook, metadata
and other setup information.
+ [Note to RFC Editor: All references to RFC XXXX are to be replaced
+ by references to the RFC number of this memo, when published.]
-
-
-
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Table of Contents
1. Introduction ........................................ 2
- 1.1 Terminology ......................................... 3
+ 1.1 Terminology ......................................... 2
2. Payload Format ...................................... 3
2.1 RTP Header .......................................... 3
2.2 Payload Header ...................................... 4
8. Security Considerations ............................. 14
9. Acknowledgements .................................... 14
10. Normative References ................................ 14
- 10.1 Informative References ................................ 14
+ 10.1 Informative References ................................ 15
11. Full Copyright Statement ............................ 15
+ 11.1 IPR Statement ....................................... 15
12. Authors Address ..................................... 15
1 Introduction
- The Xiph.org Foundation creates and defines codecs for use in
- multimedia that are not encumbered by patents and thus may be freely
- implemented by any individual or organization.
-
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
purposes of RTP transport, this layer is unnecessary, and so raw
Vorbis packets are used in the payload.
-
-
-
-
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-
-
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2].
+
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+
+
2 Payload Format
For RTP based transportation of Vorbis encoded audio the standard
RTP header is followed by an 8 bit payload header, then the payload
- data.
+ data. The payload header is used to signify 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
used by this specification is two (2).
Padding (P): 1 bit
- If the padding bit is set, the packet contains one or more
- additional padding octets at the end which are not part of
- the payload. P is set if the total packet size is less than
- the MTU.
+ Padding MAY be used with this payload format according to
+ section 5.1 of [3].
Extension (X): 1 bit
- If the extension, X, bit is set, the fixed header MUST be
- followed by exactly one header extension, with a format defined
- in Section 5.3.1. of [4],
+ Always set to 0, as audio silence suppression is not used by
+ the Vorbis codec.
CSRC count (CC): 4 bits
- The CSRC count contains the number of CSRC identifiers.
+ The CSRC count is used in accordance with [3].
+
+
+
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Marker (M): 1 bit
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.
+ conveyed out-of-band as a SDP attribute.
SSRC/CSRC identifiers:
These two fields, 32 bits each with one SSRC field and a maximum
The last 5 bits are the number of complete packets in this payload.
This provides for a maximum number of 32 Vorbis packets in the
- payload. If C is set to one, this number SHOULD be 0.
+ payload. If C is set to one, this number MUST be 0.
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2.3 Payload Data
length.
Typical Vorbis packet sizes are from very small (2-3 bytes) to
- quite large (8-12 kilobytes). The reference implementation [9]
+ quite large (8-12 kilobytes). The reference implementation [11]
typically produces packets less than ~800 bytes, except for the
header packets which are ~4-12 kilobytes.
consists of one octet representing the packet length followed by
the packet data for each of the Vorbis packets in the payload.
- The Vorbis packet length octet is the length of the data block
- minus one.
+ The Vorbis packet length field is the length of the Vorbis data
+ block minus one octet.
The payload packing of the Vorbis data packets SHOULD follow the
guidelines set-out in section 4.4 of [5] where the oldest packet
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Payload Data:
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
- Final Fragment (F) bit set to one. To maintain the correct sequence
+ 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.
+ number incremented as normal for the subsequent RTP packets. Path
+ MTU is detailed in [9] and [10].
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Packet 1:
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 MTU of 1500 octets, 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.
+ than the path MTU, including all RTP and payload headers. The
+ sequence number has been incremented by one but the timestamp field
+ remains the same as the initial packet.
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Packet 3:
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, MUST be dropped
- in the same manner. Feedback reports on lost and dropped packets
- MUST be sent back via RTCP.
+ 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.
4 Configuration Headers
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As the RTP stream may change certain configuration data mid-session
The three header data blocks are sent out-of-band as an APP defined
RTCP message with the 4 octet name field set to VORB.
- VORB RTCP packets MUST set the padding (P) flag and add the
- appropriate padding octets needed to conform with section 6.6
- of [3]. Synchronizing the configuration headers to the RTP stream
- is critical. A 32 bit timestamp field is used to indicate the
+ Synchronizing the configuration headers to the RTP stream is
+ critical. A 32 bit timestamp field is used to indicate the
timepoint when a VORB header MUST be applied to the RTP stream.
- VORB RTCP packets MUST be sent just ahead of the change in the RTP
- stream. As the reception loss of the RTCP header will mean the
- RTP stream will fail to decode properly the freqency of their
- periodic retransmission MUST be high enough to minimize the
+ VORB RTCP packets SHOULD be sent just ahead of the change in the
+ RTP stream. As the reception loss of the RTCP header will mean
+ the RTP stream will fail to decode properly the freqency of their
+ periodic retransmission SHOULD be high enough to minimize the
stream disturbance whilst remaining under the RTCP bandwidth
allocation.
| Bitrate Nominal |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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0 1 2 3
If the c flag is set then the next header block will contain the
codebook configuration data.
- This setup information MUST be completely intact, as a client can
- not decode a stream with an incomplete or corrupted codebook set.
+ The configuration information detailed above MUST be completely
+ intact, as a client can not decode a stream with an incomplete
+ or corrupted codebook set.
A 16 bit codebook length field and a 16 bit 1's complement checksum
of the codebook precedes the codebook datablock. The length field
allows for codebooks to be up to 64K in size. The checksum is used
to detect a corrupted codebook.
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If a checksum failure is detected then a new config header file
session faster. When a client receives a codebook it may store
it, together with the MD5 key, locally and can compare the MD5 key
of locally cached codebooks with the key it receives via SDP, which
- is detailed in section 5.1.
+ is detailed in section 5.
5 Session Description for Vorbis RTP Streams
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Below is an outline of the mandatory SDP attributes.
- u=<URI of Vorbis header file>
+ c=IN IP4/6 <Vorbis stream>
m=audio <port> RTP/AVP 98
- c=IN IP4/6 <URI of Vorbis stream>
a=rtpmap:98 vorbis/<sample rate>
-
- The contents of the Vorbis Header file referred to in the
- u attribute MUST contain all three of the config header blocks
- as specified in section 4. The overflow bit of the header packet
- MUST not be set.
+ a=fmtp:98 header=<URI of Vorbis codebooks>
+ a=fmtp:98 md5key=<MD5 key of codebook>
The port value is specified by the server application bound to
- the URI specified in the c attribute. The bitrate value specified
- in the a attribute MUST match the Vorbis sample rate value.
+ the address specified in the c attribute. The bitrate value
+ specified in the a attribute MUST match the Vorbis sample rate
+ value.
+
+ The Vorbis codebook specified in the header attribute MUST contain
+ all of the configuration data. If the codebook MD5 attribute,
+ md5key, is set the key is compared to a locally held cache and
+ if found the associated local codebook is used, if not the
+ client MUST use the configuration headers specified with the
+ header attribute.
5.1 SDP Based Config Header Transmission
of the mandatory and optional SDP attributes MUST be less than
1K in size to conform to section 4.1 of [8].
- a=md5key:<MD5 key of codebook>
- a=bitrate_min:<Bitrate Minimum>
- a=bitrate_norm:<Bitrate Normal>
- a=bitrate_max:<Bitrate Maximum>
- a=bsz0:<Block Size 0>
- a=bsz1:<Block Size 1>
- a=channels:<Num Audio Channels>
- a=meta_vendor:<Vendor Name>
-
- If the codebook MD5 attribute, md5key, is set the key is compared
- to a locally held cache and if found the associated local codebook
- is used, if not the client MUST use the configuration headers
- specified in the u attribute.
+ a=fmtp:98 bitrate_min=<Bitrate Minimum>
+ a=fmtp:98 bitrate_norm=<Bitrate Normal>
+ a=fmtp:98 bitrate_max=<Bitrate Maximum>
+ a=fmtp:98 bsz0=<Block Size 0>
+ a=fmtp:98 bsz1=<Block Size 1>
+ a=fmtp:98 channels=<Num Audio Channels>
+ a=fmtp:98 meta_vendor=<Vendor Name>
- The md5key requires other attributes which detail bitrates, channels
- and metadata associated with the RTP stream. The attributes
- following the md5key example above MUST all be present.
The metadata attribute, meta_vendor, provides the bare minimum
information required for decoding but does not convey any
- meaningfull stream metadata information. As outlined in the Vorbis
+ meaningful stream metadata information. As outlined in the Vorbis
comment field and header specification documentation, [7], a number
of predefined field names are available which SHOULD be used. An
example would be:
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- a=meta_vendor:Xiph.Org libVorbis I 20020717
- a=meta_artist:Honest Bob and the Factory-to-Dealer-Incentives
- a=meta_title:I'm Still Around
- a=meta_tracknumber:5
+ a=fmtp:98 meta_vendor=Xiph.Org libVorbis I 20020717
+ a=fmtp:98 meta_artist=Honest Bob and the Factory-to-Dealer-Incentives
+ a=fmtp:98 meta_title=I'm Still Around
+ a=fmtp:98 meta_tracknumber=5
6 IANA Considerations
MIME subtype: vorbis
- Required Parameters: none
+ Required Parameters:
+ header indicates the URI of the decoding codebook.
+ md5key indicates the MD5 key of the codebooks.
- Optional Parameters: none
+ Optional Parameters:
+ bitrate_min, bitrate_norm and bitrate_max indicate the
+ minimum, nominal and maximum bitrates. bsz0 and bsz1
+ indicate the blocksize values. channels indicates the
+ number of audio channels in the stream. meta_vendor
+ indicates the encoding codec vendor.
Encoding considerations:
- This type is only defined for transfer via RTP as specified in
- a Work in Progress.
+ This type is only defined for transfer via RTP as specified
+ in RFC XXXX.
Security Considerations:
See Section 6 of RFC 3047.
Person & email address to contact for further information:
Phil Kerr
- philkerr@elec.gla.ac.uk
+ philkerr@elec.gla.ac.uk/phil@plus24.com
Intended usage: COMMON
Author/Change controller:
Author: Phil Kerr
- Change controller: Phil Kerr
-
+ Change controller: IETF AVT Working Group
7 Congestion Control
so an alternative would be to redirect the client to a lower
bitrate stream if one is available.
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8 Security Considerations
Thanks to the AVT, Ogg Vorbis Communities / Xiph.org including
Steve Casner, Ramon Garcia, Pascal Hennequin, Ralph Jiles,
Tor-Einar Jarnbjo, Colin Law, John Lazzaro, Jack Moffitt,
- Colin Perkins, Barry Short, Mike Smith.
+ Colin Perkins, Barry Short, Mike Smith, Magnus Westerlund.
10 Normative References
- 1. The Ogg Encapsulation Format Version 0 (RFC 3533), S. Pfeiffer.
+ 1. The Ogg Encapsulation Format Version 0 (RFC 3533), S. Pfeiffer.
- 2. Key words for use in RFCs to Indicate Requirement Levels
- (RFC 2119), S. Bradner.
+ 2. Key words for use in RFCs to Indicate Requirement Levels
+ (RFC 2119), S. Bradner.
- 3. RTP: A Transport Protocol for Real-Time Applications (RFC 1889),
- Schulzrinne, et al.
+ 3. RTP: A Transport Protocol for Real-Time Applications (RFC 1889),
+ Schulzrinne, et al.
- 4. RTP: A transport protocol for real-time applications. Work
- in progress, draft-ietf-avt-rtp-new-11.txt.
+ 4. RTP: A transport protocol for real-time applications. Work
+ in progress, draft-ietf-avt-rtp-new-11.txt.
- 5. RTP Profile for Audio and Video Conferences with Minimal Control.
- Work in progress, draft-ietf-avt-profile-new-12.txt.
+ 5. RTP Profile for Audio and Video Conferences with Minimal Control.
+ Work in progress, draft-ietf-avt-profile-new-12.txt.
- 6. Ogg Vorbis I spec: Codec setup and packet decode.
- http://www.xiph.org/ogg/vorbis/doc/vorbis-spec-ref.html
+ 6. Ogg Vorbis I spec: Codec setup and packet decode.
+ http://www.xiph.org/ogg/vorbis/doc/vorbis-spec-ref.html
- 7. Ogg Vorbis I spec: Comment field and header specification.
- http://www.xiph.org/ogg/vorbis/doc/v-comment.html
+ 7. Ogg Vorbis I spec: Comment field and header specification.
+ http://www.xiph.org/ogg/vorbis/doc/v-comment.html
+
+ 8. SDP: Session Description Protocol (RFC 2327), Handley, M. and
+ V. Jacobson.
+
+ 9. Path MTU Discovery (RFC 1063), Mogul & Deering
+
+ 10. Path MTU Discovery for IP version 6 (RFC 1981), McCann, J. et al.
- 8. SDP: Session Description Protocol (RFC 2327), Handley, M. and
- V. Jacobson.
-10.1 Informative References
- 9. libvorbis: Available from the Xiph website, http://www.xiph.org
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+
+
+10.1 Informative References
+
+ 11. libvorbis: Available from the Xiph website, http://www.xiph.org
+
11 Full Copyright Statement
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+10.1 IPR Statement
+
+ "The IETF takes no position regarding the validity or scope of\r any intellectual property or other rights that might be claimed\r to pertain to the implementation or use of the technology\r described in this document or the extent to which any license\r under such rights might or might not be available; neither does\r it represent that it has made any effort to identify any such\r rights. Information on the IETF's procedures with respect to\r rights in standards-track and standards-related documentation\r can be found in BCP-11. Copies of claims of rights made\r available for publication and any assurances of licenses to\r be made available, or the result of an attempt made\r to obtain a general license or permission for the use of such\r proprietary rights by implementors or users of this\r specification can be obtained from the IETF Secretariat."
+
+ Further IPR details on the Vorbis bitstream may be found on the
+ Xiph website: http://www.xiph.org
+
+
12 Authors Address
WWW: http://www.xiph.org/
-
-
-
-
-
-
-
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-
-
-From: Colin Perkins <csp@csperkins.org>
-Date: Tue May 6, 2003 23:29:25 Europe/London
-To: philkerr@elec.gla.ac.uk
-Cc: avt@ietf.org
-Subject: [AVT] Re: Status of draft-kerr-avt-vorbis-rtp-01
-
-Hi Phil,
-
---> philkerr@elec.gla.ac.uk writes:
-I'm checking on the status of draft-kerr-avt-vorbis-rtp-01 and how things can be
-moved forward with it. The update was submitted just before the cutoff for the
-last AVT meeting and there seems to have been no action on it since.
-
-I took the liberty of cc'ing the AVT mailing list, to encourage feedback.
-
-There are a few small changes I may wish to make to the draft, which will be
-discussed at a Vorbis meeting tomorrow, but I wanted to check with you first on
-if the 01 draft is good enough to move forward.
-
-I think it's in good shape, although I have a couple of issues:
-
- - Section 2.1 notes that the P, X and CC fields of the RTP header are set
- to 0. I'm not sure it's appropriate for a payload format to specify this:
- I can imagine valid scenarios where each of these can be used with Vorbis. *
-
- - The discussion in section 3 can make use of normative language to be
- clear on how frames are packetized. I suggest the following changes:
-
- Any Vorbis packet that is larger than 256 octets and less than the
- path-MTU should be placed in a RTP packet by itself.
- ^^^^^^ MUST
-*
- Any Vorbis packet that is 256 bytes or less should be bundled in the
- ^^^^^^ SHOULD
- RTP packet with as many Vorbis packets as will fit, up to a maximum
- of 32.
-*
- If a Vorbis packet will not fit into the RTP packet, it must be
- within the network MTU ^^^^^^^^^^^^^^^^^^^ ^^^^ SHOULD
- fragmented. A fragmented packet has a zero in the last five 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
- Marker (F) bit set to one.
- ^^^^^^ Final Fragment
- (to avoid confusion with the RTP Marker bit)
-*
-
- - The IANA considerations section needs to be expanded. Section 4 of RFC
- 3047 is a good example, to illustrate the format. *
-
- - Regarding the configuration headers, is there a need to send updates
- during a session? If not, it might be appropriate to define some SDP
- parameters to convey the configuration data at session initiation time,
- rather than relying on RTCP. If RTCP is to be used, it's necessary to
- discuss reliability, and how a receiver reacts if the information is
- lost.
-
-I also have a few editorial comments:
-
- - The interpretation of key words and reference to RFC 2119 should be
- moved into the Introduction rather than being in the Status of this
- Memo section. *
-
- - I suggest moving the last three paragraphs of the Introduction into
- section 2.3, where the packing of the payload data is discussed. It
- may also be appropriate to include a slightly longer description of
- the Vorbis codec and when it might be useful in the Introduction. *
-
- - In section 3.1, it might be useful to include the RTP packet header
- details, to show how the RTP sequence number and timestamp are used
- (sequence number increases by one for each packet, timestamp stays
- the same for each fragment). *
-
- - Section 7 might reference the discussion of congestion control in
- the RTP spec and/or profile
-
- - References should be split into Normative and Informative sections. *
-
-
-Cheers,
-Colin
-_______________________________________________
-Audio/Video Transport Working Group
-avt@ietf.org
-https://www1.ietf.org/mailman/listinfo/avt
-
-
-
-
-
-Hi All,
-
-Please find below an updated Vorbis-RTP Internet Draft document for review and discussion at the Xiph IRC meeting on Saturday.
-
-The changes in this version have been:
-
-Codebook caching mechanism
-Expanded SDP parameters
-Expanded MIME section
-Expanded introduction
-Packet loss section
-Minor tweaks and clarity changes to text
-
-There are probably some minor tweaks to the formatting needed which will be done before the final submission.
-
-Open issues concern:
-
-Bitrate peeling for congestion control needs to be firmed up
-A clearer definition of the path MTU is probably needed
-
-Feedback and comments welcomed of course.
-
-All being well I will submit this to the IETF early next week with a request to move the document to AVT WG status (a step closer to RFC).
-
-Regards
-
-Phil
-
-
-Annexe) some comments on draft-kerr-avt-vorbis-rtp-01 :
- - Section 3, p5. "path-MTU" is not a clear concept in IP multicast.
- (path-mtu discover algorithm not operationnal here)
- Open issue : optimal value for a "RTP-MTU" with vorbis ?
- (IP fragmentation/reassembling vs RTP framentation/reassembling ?)
- (size and frequency of "big" vorbis packet ?)
- (optimistic MTU=1500, pessimistic MTU=500, Neutral MTU=1000 ?) *?
-
- - Section 5, p.9 last paragraph. "the URI value set there" is in SDP *
- information or in VORB RTCP overflow field ?
-
- - Section 5 sentence "The framing bit is not used for RTP ..." appears *
- 2 times.
-
- - Section 6, c=IN IP4 .. ; no reason to restrict to IPv4 *
-
- - Section 6, needs clarification for "all three of the config header *
- blocks". starting of the first block ?
-
- - Section 2.2, figure, numbering from 0 to 7 is better *
-
- - Need rules for reassembling process (Section 3.2 ?).
- Normal process
- misordering ?
- process with loss of fragment ? temporisation ?? *
-
- - More generally what is the consequence of vorbis packet loss,
- and vorbis packet misordeing ?
- - ...
-
-
-
projects / platform / upstream / libvorbis.git / commitdiff