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