(RFC 4184 published October 2005, subtype last updated October 2005)

o Type name:                         audio

o Subtype name:                      ac3

o Required parameters:

  rate: The RTP timestamp clock rate that is equal to the audio
	 sampling rate.  Permitted rates are 32000, 44100, and 48000.

o Optional parameters:

  channels: From a sender, the maximum number of channels present in
	 the AC3 stream.  From a receiver, the maximum number of output
	 channels the receiver will deliver.  This MUST be a number
	 between 1 and 6.  The LFE (".1") channel MUST be counted as one
	 channel.  Note that the channel order used in AC-3 differs from
	 the channel order scheme in [RFC3551].  The AC-3 channel order
	 scheme can be found in Table 5.8 of [ATSC].

  ptime: See RFC 2327 [RFC2327].

  maxptime: See RFC 3267 [RFC3267].

o Encoding considerations:

	 This media type is framed (see section 4.8 in [DRAFT-FREED])
	 and contains binary data.

o Security considerations:

	 See Section 6 of this document.

o Interoperability considerations:

	 None

o Published specification:

	 This payload format specification and see [ATSC].

o Applications that use this media type:

	 Multichannel audio compression of audio and audio for video.

o Additional Information:

	 Magic number(s):
			 The first two octets of an AC-3 frame are always the
			 synchronization word, which has the hex value 0x0B77.

o Person & email address to contact for further information:

	 Brian Link <bdl&dolby.com>
	 IETF AVT working group.

o Intended Usage:

	 COMMON

o Restrictions on usage:

	 This media type depends on RTP framing, and hence is only
	 defined for transfer via RTP [RFC3550].  Transport within other
	 framing protocols is not defined at this time.

Author/Change controller:

	 IETF Audio/Video Transport Working Group delegated from the
	 IESG.