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AVT Working Group L. Barbato
Internet-Draft Xiph.Org
Expires: April 24, 2006 October 21, 2005
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
+ 3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 13
4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 13
- 5. Frame Packetization . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . 20
- 8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
- 8.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 20
- 9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
- 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
- 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
- 11.1. Normative References . . . . . . . . . . . . . . . . . . . 21
- 11.2. Informative References . . . . . . . . . . . . . . . . . . 22
- Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
- Intellectual Property and Copyright Statements . . . . . . . . . . 24
+ 5. Frame Packetization . . . . . . . . . . . . . . . . . . . . . 14
+ 5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 15
+ 5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 17
+ 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
+ 6.1. Mapping MIME Parameters into SDP . . . . . . . . . . . . . 19
+ 6.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 20
+ 7. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 21
+ 8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
+ 8.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 21
+ 9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
+ 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
+ 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
+ 11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
+ 11.2. Informative References . . . . . . . . . . . . . . . . . . 23
+ Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25
+ Intellectual Property and Copyright Statements . . . . . . . . . . 26
2 = Legacy Vorbis Comment payload
3 = Reserved
+ The packets with a TDT of value 3 MUST be ignored
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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
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. Subsequence packets, if any, MUST
- follow in temporal order.
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+ after the RTP packet header. Subsequence packets, if any, MUST
+ follow in temporal order.
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Channel mapping of the audio is in accordance with the Vorbis I
Specification [15].
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.
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+ 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.
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3. Configuration Headers
Unlike other mainstream audio codecs Vorbis has no statically
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
- 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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+ 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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3.1. In-band Header Transmission
The Packed Configuration (Section 3.1.1) Payload is sent in-band with
client provide a minimal size comment header to the decoder if
required by the implementation.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
3.2.1. Packed Headers
As mentioned above the RECOMMENDED delivery vector for Vorbis
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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
length there is only a 2 byte length tag to define the length of the
packed headers.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following IANA considerations MUST only be applied to the packed
headers.
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MIME media type name: audio
MIME subtype: vorbis-config
See Section 6 of RFC XXXX.
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Interoperability considerations:
None
Intended usage: COMMON
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Restriction on usage:
This media type doesn't depend on the transport.
report sent via RTCP.
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4. Comment Headers
With the payload type flag set to 2, this indicates that the packet
completely. The details on the format of the comments can be found
in the Vorbis documentation [15].
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
application's desired transmission latency. Path MTU is detailed in
[6] and [7].
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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
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
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packets MUST be the same as the first packet sent, with the sequence
number incremented as normal for the subsequent RTP packets. The
length field shows the fragment length.
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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 voice,
+ The content itself could be a mix of live stream, as the wj's voice,
and stored streams as the music she plays.
In this situation we don't know in advance how many codebooks we will
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 as soon it joins the session.
+ to decode the current stream inlined in the SDP so that the decoding
+ will start immediately after.
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. Since the inline method is
- unreliable, an out of band fallback is provided. The client could
- choose to fetch the Configuration from the alternate source as soon
- it discovers a Configuration packet got lost inline or use selective
- retransmission [17], if the server supports that feature.
+ unreliable, an out of band fallback is provided.
+ The client could choose to fetch the Configuration from the alternate
+ source as soon it discovers a Configuration packet got lost inline or
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+ use selective retransmission [17], if the server supports that
+ feature.
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A serverside optimization would be to keep an hash list of the
Configurations per session to avoid packing all of them and send the
same Configuration with different Ident tags
[1] Pfeiffer, S., "The Ogg Encapsulation Format Version 0",
RFC 3533.
- [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
- Levels", RFC 2119.
-
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+ [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
+ Levels", RFC 2119.
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[3] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for real-time applications",
RFC 3550.
specification. Available from the Xiph website,
http://www.xiph.org".
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[17] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol
Extended Reports (RTCP XR)", RFC 3611, November 2003.
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projects / platform / upstream / libvorbis.git / commitdiff