(RFC 3555 published July 2003) MIME media type name: audio MIME subtype name: MPA (MPEG audio) Required parameters: None Optional parameters: layer: which layer of MPEG audio encoding; permissible values are 1, 2, 3. samplerate: the rate at which audio is sampled. MPEG-1 audio supports sampling rates of 32, 44.1, and 48 kHz; MPEG-2 supports sampling rates of 16, 22.05 and 24 kHz. This parameter is separate from the RTP timestamp clock rate which is always 90000 Hz for MPA. mode: permissible values are "stereo", "joint_stereo", "single_channel", "dual_channel". The "channels" parameter does not apply to MPA. It is undefined to put a number of channels in the SDP rtpmap attribute for MPA. bitrate: the data rate for the audio bit stream. ptime: RECOMMENDED duration of each packet in milliseconds. maxptime: maximum duration of each packet in milliseconds. Parameters which are omitted are left to the encoder to choose based on the session bandwidth, configuration information, or other constraints. The selected layer as well as the sampling rate and mode are indicated in the payload so receivers can process the data without these parameters being specified externally. Encoding considerations: This type is only defined for transfer via RTP [RFC 3550]. Security considerations: See Section 5 of RFC 3555 Interoperability considerations: none Published specification: RFC 3551 Applications which use this media type: Audio and video streaming and conferencing tools. Additional information: none Person & email address to contact for further information: Stephen Casner Intended usage: COMMON Author/Change controller: Stephen Casner