AVT Working Group L. Barbato
Internet-Draft Xiph.Org
-Expires: October 19, 2007 April 17, 2007
+Expires: November 5, 2007 May 04, 2007
- draft-ietf-avt-rtp-vorbis-03
+ draft-ietf-avt-rtp-vorbis-04
RTP Payload Format for Vorbis Encoded Audio
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 October 19, 2007.
+ This Internet-Draft will expire on November 5, 2007.
Copyright Notice
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Editors Note
5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 13
5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
- 6.1. Packed Headers IANA Considerations . . . . . . . . . . . . 18
+ 6.1. Packed Headers IANA Considerations . . . . . . . . . . . . 19
7. SDP related considerations . . . . . . . . . . . . . . . . . . 20
7.1. Mapping MIME Parameters into SDP . . . . . . . . . . . . . 20
7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 21
8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 21
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 22
- 10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
+ 10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
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0 1 2 3
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Sequence number: 16 bits
A timestamp representing the sampling time of the first sample of the
first Vorbis packet in the RTP packet. The clock frequency MUST be
set to the sample rate of the encoded audio data and is conveyed out-
- of-band as a SDP parameter.
+ of-band (e.g. as a SDP parameter).
SSRC/CSRC identifiers:
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This field specifies the kind of Vorbis data stored in this RTP
packet. There are currently three different types of Vorbis
payloads. Each packet MUST contain only a single type of Vorbis
- payload.
+ payload (e.g. you MUST not aggregate configuration and comment
+ payload in the same packet)
0 = Raw Vorbis payload
1 = Vorbis Packed Configuration payload
Each Vorbis payload packet starts with a two octet length header,
which is used to represent the size in bytes of the following data
payload, followed by the raw Vorbis data padded to the nearest byte
- boundary. The length value is stored as network byte order integer.
+ boundary, as explained by the vorbis specification [12]. The length
+ value is stored as network byte order integer.
For payloads which consist of multiple Vorbis packets the payload
data consists of the packet length followed by the packet data for
each of the Vorbis packets in the payload.
- The Vorbis packet length header is the length of the Vorbis data
- block only and does not count the length field.
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+
+ The Vorbis packet length header is the length of the Vorbis data
+ block only and does not count the length field.
The payload packing of the Vorbis data packets MUST follow the
guidelines set-out in [3] where the oldest packet occurs immediately
| contributing source (CSRC) identifiers |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-
- Figure 4: Example Packet (RTP Headers)
-
- Payload Data:
-
- 0 1 2 3
- 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ident | 0 | 0 | 2 pks |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | length | vorbis data ..
+ | length | vorbis data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| length | next vorbis packet data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- .. vorbis data |
+ .. vorbis data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ .. vorbis data |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 5: Example Packet (Payload Data)
+ Figure 4: Example Raw Vorbis Packet
The payload data section of the RTP packet begins 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
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- 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 octets length field. The Packet Type and
Fragment Type are set to 0. The Configuration that will be used to
decode the packets is the one indexed by the ident value.
Unlike other mainstream audio codecs Vorbis has no statically
configured probability model. Instead, it packs all entropy decoding
- configuration, VQ and Huffman models into a data block that must be
- transmitted to the decoder along with the compressed data. A decoder
- also requires information detailing the number of audio channels,
- bitrates and similar information to configure itself for a particular
- compressed data stream. These two blocks of information are often
- referred to collectively as the "codebooks" for a Vorbis stream, and
- are nominally included as special "header" packets at the start of
- the compressed data. In addition, the Vorbis I specification [12]
- requires the presence of a comment header packet which gives simple
- metadata about the stream, but this information is not required for
- decoding the frame sequence.
+ configuration, Vector Quantization and Huffman models into a data
+ block that must be transmitted to the decoder along with the
+ compressed data. A decoder also requires information detailing the
+ number of audio channels, bitrates and similar information to
+ configure itself for a particular compressed data stream. These two
+ blocks of information are often referred to collectively as the
+ "codebooks" for a Vorbis stream, and are nominally included as
+ special "header" packets at the start of the compressed data. In
+ addition, the Vorbis I specification [12] requires the presence of a
+ comment header packet which gives simple metadata about the stream,
+ but this information is not required for decoding the frame sequence.
Thus these two codebook header packets must be received by the
decoder before any audio data can be interpreted. These requirements
stream may change certain configuration data mid-session, there are
different methods for delivering this configuration data to a client,
both in-band and out-of-band which is detailed below. SDP delivery
- is used to set up an initial state for the client application. The
- changes may be due to different codebooks as well as different
- bitrates of the stream.
+ is typically used to set up an initial state for the client
+ application. The changes may be due to different codebooks as well
+ as different bitrates of the stream.
- The delivery vectors in use are specified by an SDP attribute to
+ 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
delivery methods that don't use RTP will not be described in this
document. For non chained streams, the Configuration recommended
delivery method is inline the Packed Configuration (Section 3.1.1) in
- the SDP as explained in the IANA considerations (Section 7.1)
- section.
+ the SDP as explained in the IANA considerations (Section 7.1).
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
+ 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
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- 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.
A Vorbis Packed Configuration is indicated with the Vorbis Data Type
field set to 1. Of the three headers, defined in the Vorbis I
- specification [12], the identification and the setup will be packed
- together, the comment header is completely suppressed. Is up to the
- client to provide a minimal size comment header to the decoder if
- required by the implementation.
+ specification [12], the identification and the setup MUST be packed
+ together, while the comment header MUST be completely suppressed. Is
+ up to the client to provide a minimal size comment header to the
+ decoder if required by the implementation.
+
+
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0 1 2 3
.. Setup |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 6: Packed Configuration Figure
+ Figure 5: Packed Configuration Figure
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
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3.2.1. Packed Headers
using a reliable transport protocol. As the RTP headers are not
required for this method of delivery the structure of the
configuration data is slightly different. The packed header starts
- with a 32 bit count field which details the number of packed headers
- that are contained in the bundle. Next is the Packed header payload
- for each chained Vorbis stream.
+ with a 32 bit (network ordered) count field which details the number
+ of packed headers that are contained in the bundle. Next is the
+ Packed header payload for each chained Vorbis stream.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of packed headers |
| Packed header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 7: 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
.. Setup Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 8: Packed Headers Detail
+ Figure 7: Packed Headers Detail
The key difference between the in-band format and this one, is there
is no need for the payload header octet.
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3.3. Loss of Configuration Headers
.. Comment |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 9: Comment Packet
+ Figure 8: Comment Packet
The 2 bytes length field is necessary since this packet could be
fragmented.
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5. Frame Packetization
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Packet 1:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | 1000 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | xxxxx |
+ | 12345 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
.. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 10: Example Fragmented Packet (Packet 1)
+ Figure 9: Example Fragmented Packet (Packet 1)
In this packet the initial sequence number is 1000 and the timestamp
- is xxxxx. The Fragment type is set to 1, the number of packets field
+ is 12345. The Fragment type is set to 1, the number of packets field
is set to 0, and as the payload is raw Vorbis data the VDT field is
set to 0.
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Packet 2:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | 1001 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | xxxxx |
+ | 12345 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
.. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 11: Example Fragmented Packet (Packet 2)
+ Figure 10: Example Fragmented Packet (Packet 2)
The Fragment type field is set to 2 and the number of packets field
is set to 0. For large Vorbis fragments there can be several of
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Packet 3:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | 1002 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | xxxxx |
+ | 12345 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
.. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- Figure 12: Example Fragmented Packet (Packet 3)
+ Figure 11: Example Fragmented Packet (Packet 3)
This is the last Vorbis fragment packet. The Fragment type is set to
3 and the packet count remains set to 0. As in the previous packets
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6. IANA Considerations
Control. [3]
delivery-method: indicates the delivery methods in use, the
- possible values are: inline, in_band, out_band
+ possible values are: inline, in_band, out_band, MAY be included
+ multiple times
configuration: the base64 [8] representation of the Packed
- Headers (Section 3.2.1).
+ Headers (Section 3.2.1). It MUST follow the associated
+ delivery-method parameter ("inline").
Optional parameters:
applies, a "!" and the base64 [8] representation of the
sha1hash of the above mentioned compressed aggregated as in:
"protocol://path/to/resource/aggregated.bz2!sha1hash". The
- trailing '/' discriminates which of two methods are in use.
+ trailing '/' discriminates which of two methods are in use. It
+ MUST follow the associated delivery method parameter (either
+ "in_band" or "out_band").
Encoding considerations:
This media type is framed and contains binary data.
- Security considerations:
- See Section 10 of RFC XXXX.
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+ Security considerations:
+ See Section 10 of RFC XXXX.
Interoperability considerations:
IETF AVT Working Group delegated from the IESG
-6.1. Packed Headers IANA Considerations
-
- The following IANA considerations MUST only be applied to the packed
- headers.
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+6.1. Packed Headers IANA Considerations
+
+ The following IANA considerations MUST only be applied to the packed
+ headers.
+
Type name: audio
Subtype name: vorbis-config
Luca Barbato: <lu_zero@gentoo.org>
IETF Audio/Video Transport Working Group
- Intended usage: COMMON
-
-
-
-
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+ Intended usage: COMMON
+
Restriction on usage:
This media type doesn't depend on the transport.
7.1. Mapping MIME Parameters into SDP
- The information carried in the MIME media type specification has a
- specific mapping to fields in the Session Description Protocol (SDP)
- [4], which is commonly used to describe RTP sessions. When SDP is
- used to specify sessions the mapping are as follows:
+ The information carried in the Media Type media type specification
+ has a specific mapping to fields in the Session Description Protocol
+ (SDP) [4], which is commonly used to describe RTP sessions. When SDP
+ is used to specify sessions the mapping are as follows:
- o The MIME type ("audio") goes in SDP "m=" as the media name.
+ o The type name ("audio") goes in SDP "m=" as the media name.
- o The MIME subtype ("vorbis") goes in SDP "a=rtpmap" as the encoding
+ o The subtype name ("vorbis") goes in SDP "a=rtpmap" as the encoding
name.
o The parameter "rate" also goes in "a=rtpmap" as clock rate.
o The parameter "channels" also goes in "a=rtpmap" as channel count.
o The mandated parameters "delivery-method" and "configuration" MUST
- be included in the SDP "a=fmpt" attribute.
+ be included in the SDP "a=fmtp" attribute.
o The optional parameter "configuration-uri", when present, MUST be
- included in the SDP "a=fmpt" attribute and MUST follow the
+ 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
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+ The URI specified in the configuration-uri attribute MUST point to a
+ location where all of the Configuration Packets needed for the life
of the session reside.
The port value is specified by the server application bound to the
- address specified in the c attribute. The bitrate value and channels
+ address specified in the c= line. The bitrate value and channels
specified in the rtpmap attribute MUST match the Vorbis sample rate
value. An example is found below.
could be fetched at any time from the first provided uri using or all
the known configuration could be downloaded using the second uri.
The inline base64 [8] configuration string is omitted because of the
- lenght.
+ length.
c=IN IP4 192.0.2.1
m=audio RTP/AVP 98
a=rtpmap:98 vorbis/44100/2
8. Congestion Control
Vorbis clients SHOULD send regular receiver reports detailing
- congestion. A mechanism for dynamically downgrading the stream,
- known as bitrate peeling, will allow for a graceful backing off of
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+ congestion. A mechanism for dynamically downgrading the stream,
+ known as bitrate peeling, will allow for a graceful backing off of
the stream bitrate. This feature is not available at present so an
alternative would be to redirect the client to a lower bitrate stream
if one is available.
already known.
-10. Security Considerations
- RTP packets using this payload format are subject to the security
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+10. Security Considerations
+
+ RTP packets using this payload format are subject to the security
considerations discussed in the RTP specification [2]. This implies
that the confidentiality of the media stream is achieved by using
encryption. Because the data compression used with this payload
format is applied end-to-end, encryption may be performed on the
- compressed data. Where the size of a data block is set care MUST be
- taken to prevent buffer overflows in the client applications.
+ 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.
11. Acknowledgments
[5] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
- [6] McCann et al., J., "Path MTU Discovery for IP version 6",
- RFC 1981.
-
- [7] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
-
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+ [6] McCann et al., J., "Path MTU Discovery for IP version 6",
+ RFC 1981.
+
+ [7] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264.
[8] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
-
-
-
-
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Full Copyright Statement
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projects / platform / upstream / libvorbis.git / commitdiff