(RFC 5584 published July 2009, subtype last updated July 2009)

Type name:  audio

Subtype name:  ATRAC3

Required parameters:

rate:  Represents the sampling frequency in Hz of the original audio
data.  Permissible value is 44100 only.

baseLayer:  Indicates the encoded bit-rate in kbps for the audio data
to be streamed.  Permissible values are 66, 105, and 132.

Optional parameters:

ptime:  See RFC 8866.

maxptime:  See RFC 8866.
The frame length of ATRAC3 is 1024/44100 = 23.22...(ms), and
fractional value may not be applicable for the SDP definition.

So the value of the parameter MUST be a multiple of 24 (ms)
considering safe transmission.

If this parameter is not present, the sender MAY encapsulate a
maximum of 6 encoded frames into one RTP packet, in streaming of
ATRAC3.

maxRedundantFrames:  The maximum number of redundant frames that may
be sent during a session in any given packet under the redundant
framing mechanism detailed in the document.  Allowed values are
integers in the range of 0 to 15, inclusive.  If this parameter is
not used, a default of 15 MUST be assumed.

Encoding considerations:  This media type is framed and contains
binary data.

Security considerations:  This media type does not carry active
content.  See Section 9 of RFC 5584.

Interoperability considerations:  none

Published specification:  ATRAC3 Standard Specification [9]

Applications that use this media type:
Audio and video streaming and conferencing tools.

Additional information:  none
Magic number(s):  none
File extension(s):  'at3', 'aa3', and 'omg'
Macintosh file type code(s):  none

Person and email address to contact for further information:
Mitsuyuki Hatanaka
Jun Matsumoto
actech&jp.sony.com

Intended usage:  COMMON

Restrictions on usage:  This media type depends on RTP framing, and
hence is only defined for transfer via RTP.

Author:
Mitsuyuki Hatanaka
Jun Matsumoto
actech&jp.sony.com

Change controller:  IETF AVT WG delegated from the IESG