Marshall & I, and others, have converged off-line on a new audio format
description. This is something Marshall & I are both happy with.
Comments are invited.
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EDITING INSTRUCTIONS
Replace section 7.7 with the text below:
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7.7 The Audio Content-Type
A Content-type of "audio" indicates that the body or body part contains
audio data. Although there is not yet a consensus on an "ideal" audio
format for use with computers, there is a pressing need for a format
capable of providing interoperable behavior.
The initial subtype of "u-law" is specified to meet this requirement.
In addition, a second subtype, "g.721", is specified to provide a
standardized means of exchanging highly-compressed audio encodings of
voice data.
The BNF for the audio type is as follows:
audio-content-type := "audio" "/" audio-subtype
*[ ";" attribute "=" value ]
audio-subtype := "u-law" / "g.721" / x-token
7.1.1 The Audio/u-law subtype
The content of this subtype is audio encoded using 8-bit ISDN u-law.
When this subtype is present, the following parameter are optional:
attribute meaning
--------- -------
"samplerate" the integer-valued number of samples/second
default value: "8000"
attribute meaning
--------- -------
"channels" the integer-valued number of interleaved channels
default value: "1"
7.1.2 The Audio/g.721 subtype
The content of this subtype is audio 8-bit ISDN u-law compressed using
the CCITT G.721 ADPCM voice data encoding scheme. When this subtype is
present, the following parameters are optional:
attribute meaning
--------- -------
"samplerate" the integer-valued number of samples/second
default value: "8000"
attribute meaning
--------- -------
"channels" the integer-valued number of interleaved channels
default value: "1"
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Add to Appendix A -- Minimal Conformance with This Memo
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6. An implementation need not support the Audio content-type value in
order to be conformant to this memo. However, if conformance to the
Audio content-type value is claimed, then the implementation must be
able to recognize the Audio/u-law subtype, and to render audio encoded
using these parameter pairings:
attribute values
---------- ------
samplerate 8000
channels 1
No conforming implementation will generate an Audio/u-law body
part that does not obey the above constraints.
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