[FFmpeg-devel] [PATCH] attachments support in matroska demuxer

Måns Rullgård mans
Sun Jan 20 19:15:50 CET 2008

Uoti Urpala <uoti.urpala at pp1.inet.fi> writes:

> On Sun, 2008-01-20 at 16:05 +0000, M?ns Rullg?rd wrote:
>> Based on what you say, I have to consider the entire concept of
>> codec_tag flawed.  Since the decoder does not in general (and
>> certainly should not) know what container the data came in, it cannot
>> know how to interpret the value of codec_tag.  Similarly a muxer,
>> whether transcoding or copying, does not know the source of the
>> codec_tag value, and thus cannot interpret it one way or another.
> You cannot always interpret the value unless you know which container it
> is from. However you CAN know the container and in that case it's better
> than nothing.
> Decoders can only map container-specific codec tags to FFmpeg-specific
> codec id values if the codec in question is known to FFmpeg (and not
> always even in that case). Demuxers in libavformat can still be useful
> even if FFmpeg does not recognize the specific codec, but that requires
> exporting the container-specific codec type information somehow.

I consider this a design flaw in FFmpeg.  I'm afraid it's well beyond
correcting now, though.

M?ns Rullg?rd
mans at mansr.com

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