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

Uoti Urpala uoti.urpala
Sun Jan 20 19:34:31 CET 2008

On Sun, 2008-01-20 at 18:15 +0000, M?ns Rullg?rd wrote:
> 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.

What exactly is a design flaw? That it exports information that allows
using it with codecs which FFmpeg itself does not recognize? And you'd
want to "correct" that so it's impossible to identify codecs from FFmpeg
demuxer output unless it's one of the codecs known by FFmpeg? That seems
absurd but I don't see what else you could mean...

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