[Matroska-devel] problem with AAC-in-Matroska

Mike Matsnev mike at po.cs.msu.su
Tue Nov 23 09:10:16 CET 2004

Moritz Bunkus wrote:
> 1. Create the appropriate elements in Matroska, invent one/some more
>    CodecID(s), and keep CodecPrivate empty.
> 2. Create one/some new CodecID(s) and explicitely say that for these the
>    CodecPrivate MUST contain the complete decoder_config.
> 3. Like 2. but also change the specs so that for all other AAC types
>    CodecPrivate MAY contain the complete decoder_config. If CodecPrivate
>    hsa been set then the demuxer can simply pass that data over to the
>    decoder. If it hasn't been set then nothing changes, because the
>    demuxers are already able to reconstruct the decoder_config for all
>    supported AAC types ("normal" and "SBR").
> 4. Do nothing. This way those "parametric stereo" files are recognized
>    as being SBR (because their sampling frequency is 24000 Hz, and the
>    standard says that all files with a sampling frequency <= 24000 Hz
>    are implicitely SBR). The problem is that two bytes of decoder_config
>    are simply lost. This may make some files undecodable.
I vote for 3. This way new files will be mostly compatible with old splitters,
and new software will simply use CodecPrivate if it's present. I suggest we
use plain "A_AAC" and set CodecPrivate for files that don't map to existing IDs.


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