[M4IF Technotes] Question on AAC object type

[Hans-Juergen Bardenhagen]

On Wednesday, 25.06.03, 10:56 Anil wrote:
> 1. Can I get an ADTS or ADIF as the transport layer for an MPEG-4
> stream?? (i guess it is yes, but just to confirm).

Not quite, because ADTS and ADIF are the header types of an AAC file  
(not a "transport layer" in the usual sense like e.g. HTTP or RTSP) that  
has not been multiplexed to a MP4 container yet. Inside this container  
the raw AAC bitstream does not have any headers anymore, because these  
informations (MPEG-x version, bitrate etc.) are handled by the MP4 file  
header then.
> 2. What is the object type index for AAC LC in case of MPEG-2 and
> MPEG-4. Does this change depending on the transport layer(ADTS or ADIF
> or GA). 3. How do I distinguish b/w MPEG-2 and MPEG-4 in case of ADIF/
> ADTS (Is it the bitstream_type and adts_id) 4. Where can I get a
> complete documentation of all these things??

A short overview of the ADTS (and ADIF) header structure is available in  
the Wiki of Audiocoding.com:
http://www.audiocoding.com/wiki/index.php?page=ADTS
If you need more informations than this, you can download the  
specifications of MPEG-2 and/or MPEG-4 AAC from the MPEG homepage or the  
MPEG Audio Subgroup (links are mentioned in the Wiki, too). This also  
refers to the question of the MP4 file format, by the way.
ZZee ya, Hans-Jürgen