A Content-Type of "audio" indicates that the body 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 "basic" is specified to meet this requirement by providing an absolutely minimal lowest common denominator audio format. It is expected that richer formats for higher quality and/or lower bandwidth audio will be defined by a later document.
The content of the "audio/basic" subtype is audio encoded using 8-bit ISDN mu-law [PCM]. When this subtype is present, a sample rate of 8000 Hz and a single channel is assumed.
The formal grammar for the content-type header field for data of type audio is given by:
audio-type := "audio" "/" ("basic" / extension-token)