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

Type name:  audio

Subtype name:  ATRAC-X

Required parameters:

rate:  Represents the sampling frequency in Hz of the original
audio data.  Permissible values are 44100 and 48000.

baseLayer:  Indicates the encoded bit-rate in kbps for the audio data
to be streamed.  Permissible values are 32, 48, 64, 96, 128, 160,
192, 256, 320, and 352.

channelID:  Indicates the number of channels and channel layout
according to the table1 in Section 7.4.  Note that this layout is
different from that proposed in RFC 3551 [3].  However, as channelID
= 0 defines an ambiguous channel layout, the channel mapping defined
in Section 4.1 of [3] could be used.  Permissible values are 0, 1, 2,
3, 4, 5, 6, 7.

Optional parameters:

ptime:  See RFC 8866.

maxptime:  See RFC 8866.
The frame length of ATRAC-X is 2048/44100 = 46.44...(ms) or
2048/48000 = 42.67...(ms), but fractional value may not be applicable
for the SDP definition.  So the value of the parameter MUST be a
multiple of 47 (ms) or 43 (ms) considering safe transmission.

If this parameter is not present, the sender MAY encapsulate a
maximum of 16 encoded frames into one RTP packet, in streaming of
ATRAC-X.

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 0 to 15, inclusive.  If this parameter is not
used, a default of 15 MUST be assumed.

delayMode:  Indicates a desire to use low-delay features, in which
case the decoder will process received data accordingly based on this
value.  Permissible values are 2 and 4.

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:  ATRAC-X Standard Specification [10]

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

Additional information:  none

Magic number(s):  none
File extension(s):  'atx', '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