[FFmpeg-cvslog] r13899 - in trunk/libavformat: isom.c mov.c

[Baptiste Coudurier]

Benoit Fouet wrote:
> Baptiste Coudurier wrote:
>> Benoit Fouet wrote:
>>   
>>> Baptiste Coudurier wrote:
>>>     
>>>
> 
> [...]
> 
>>>> IMHO the only solution is to export more that what it is atm.
>>>> What needs to be discussed is formatting and api.
>>>>
>>>> A solution which would not breaking anything would be to add
>>>> extended_codec_data field to AVCodecContext which would contain full
>>>> stsd or atoms, so original extradata is kept for backward compat.
>>>>
>>>>   
>>>>       
>>> that could be a solution, even though it would duplicate extradata when
>>> lavf knows how to handle it.
>>>     
>> lavf does not have to know how to handle extradata, it only has to
>> export it. Only codecs use extradata.
>>
>>   
> 
> well, let me rephrase: lavf has to know how to export extradata, and
> this is where I fail to see any generic way.

Not necessarly. I don't see why lavf would have to know.

What's needed by the codec is in stsd, lavf should export stsd IMHO,
this would also solve the different codec/display resolutions problem,
but yet to avoid duplication.

I already said Quicktime API export stsd in a generic way.

> for instance, for H.264 in QT, only the demuxer knows how to parse the
> atom to reformat the SPS/PPS data.
> 
>> The more generic lavf is, the better it is for its users, that's why it
>> has codec_tag field etc.. to let applications handling what lavf does
>> not know (yet).
>>
>>   
> 
> "yet" being the important word here
> that means you cannot use extradata field to handle a "generic" case

IMHO "all atoms after stsd" is far more generic than whatever butchered
data present in any frining atom nobody knows about, same for mkv.

Furthermore it is deadly simple to parse.

Wav and avi are really more simpler.

>> Only application has to know how to fetch extradata and pass it to codec.
>>
>>   
> 
> the formatting of the extradata depends on the container, no ?

Yes

> how is an application supposed to know how to parse / reformat extradata
> to pass it to the decoder ?

Documentation, API.

"mov/mp4/3gp demuxer exports in extradata all atoms present after stsd
structure" is documentation, and generic for mov/mp4/3gp.

"avi/asf/wmv/wav demuxer exports in extradata all bytes present after
WAVEFormat/Ex/Extended structure"  is documentation and generic for
avi/asf/wmv/wav.

It seems obvious that every application does this currently, see below.

>> All players not using lavf do that to use lavc decoders like qdm2/alac ...
>>

Anyway, a solution has to be found, will you jump in and propose a
solution with a patch ?

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
Smartjog USA Inc.                                http://www.smartjog.com
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