(RFC 2421 published September 1998, subtype last updated June 2004)

MIME media type name: audio

MIME subtype name: 32KADPCM

Required parameters: none

Optional parameters: none

Encoding considerations:

   Binary or Base-64 generally preferred

Security considerations:

   There are no known security risks with the sending or playing
   of raw audio data  Audio data is typically interpreted only by
   an audio codec.  Unintended information introduced into the
   data stream will result in noise.

Interoperability considerations:

   The four bit code word ordering within a byte may differ
   between existing implementations of G.726 codecs.  Since this
   content only permits the little endian ordering, codecs that
   support the opposite ordering must reorder the code words
   before storing to or retrieving from this content type.

Published specification:

   ITU-T G.726 with little endian ordering

Applications which use this media type:

   Primarily voice messaging

Additional information:

   Magic number(s): ? 
   File extension(s): .726
   Macintosh File Type Code(s):  APCM

    Little Endian Ordering:

    The 4-bit code words of the G.726 encoding MUST be packed into
    octets/bytes as follows:  the first code word (A) is placed in
    the four least significant bits of the first octet, with the
    least significant bit (LSB) of the code word (A0) in the least
    significant bit of the octet;  the second code word (B) is
    placed in the four most significant bits of the first octet,
    with the most significant bit (MSB) of the code word (B3) in
    the most significant bit of the octet. Subsequent pairs of the
    code words shall be packed in the same way into successive
    octets, with the first code word of each pair placed in the
    least significant four bits of the octet.  It is preferred
    that the voice sample be extended with silence such that the
    encoded value comprises an even number of code words.
    However, if the voice sample comprises an odd number of code
    words, then the last code word shall be discarded.

            +--+--+--+--+--+--+--+--+
            |B3|B2|B1|B0|A3|A2|A1|A0|
            +--+--+--+--+--+--+--+--+
    MSB ->  | 7| 6| 5| 4| 3| 2| 1| 0|  <- LSB
            +--+--+--+--+--+--+--+--+

            32K ADPCM / Octet Mapping

Person & email address to contact for further information:

  Glenn W. Parsons gparsons&NortelNetworks.com

  Gregory M. Vaudreuil GregV&ieee.org

Intended usage: COMMON

Author/Change controller:

  Glenn W. Parsons & Gregory M. Vaudreuil