[FFmpeg-devel] [PATCH] code to parse mpeg4audio extradata

Baptiste Coudurier baptiste.coudurier
Thu Mar 27 16:02:49 CET 2008

Michael Niedermayer wrote:
> On Thu, Mar 27, 2008 at 03:04:38PM +0100, Michael Niedermayer wrote:
>> On Thu, Mar 27, 2008 at 10:30:43AM +0100, Baptiste Coudurier wrote:
>>> Hi,
>>> Michael Niedermayer wrote:
>>>> On Thu, Mar 27, 2008 at 12:42:56AM +0100, Baptiste Coudurier wrote:
>>>>> Hi,
>>>>> Michael Niedermayer wrote:
>>>>>> On Wed, Mar 26, 2008 at 10:14:47PM +0100, Andreas ?man wrote:
>>>>>>> Michael Niedermayer wrote:
>>>>>>>> On Wed, Mar 19, 2008 at 04:54:03PM +0100, Baptiste Coudurier wrote:
>>>>>>>>> Hi,
>>>>>>>>> Here is a patch that adds parsing of mpeg4audio extradata, and retrieve
>>>>>>>>> needed infos for decoders (only mp3on4 atm, but will be needed for aac),
>>>>>>>>> and will be used by mov demuxer ideally to correctly compute sample rate
>>>>>>>>> and channels.
>>>>>>>>> Also extract common mpeg4audio code from aac_parser.c.
>>>>>>>> Iam fine with this in priciple but i am unsure if the code does not maybe
>>>>>>>> rather belong to libavformat.
>>>>>>> If the AAC decoder should reuse the code i don't think it could belong
>>>>>>> in lavf.
>>>>>> Please elaborate
>>>>>> my idea was that the mp4 demuxer would use this code to extract the various
>>>>>> thing from the mp4 atoms in .mp4 and set things like sample_rate,...
>>>>>> But maybe i misunderstood something?
>>>>> Yes, the code will also be used by mp3on4 and aac decoders to fetch
>>>>> sample rate, channels, sbr info from extradata. All decoders using
>>>>> MPEG-4 audio system will do that basically.
>>>> From what you say it sounds like this clearly belongs in the mp4 demuxer
>>>> and not in every decoder which could be stored in mp4.
>>> Huh, I don't understand.
>>> How are decoders supposed to parse extradata, AAC GASpecificConfig for
>>> example ? Duplicate the code ?
>> extradata should contain
>> GASpecificConfig/CelpSpecificConfig/HvxcSpecificConfig/... (only one of
>> these should be there)
>> The surrounding parts belong to the demuxer. The first 5? bits are yet
> After thinking about this again, iam not sure anymore, .mp4 really is a mess
> maybe it is simpler in practice to parse this in the decoders. Especially
> if one consideres raw audio streams. So iam fine with the patch in principle
> ill review it again in a moment.

Yes I agree with you, .mp4 is a whole mess, I thought it was simpler to
handle this in decoders, too, I already did it for mp3on4.

Thanks for the review.

Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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