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

Måns Rullgård mans
Sun Jan 20 17:05:21 CET 2008

Baptiste Coudurier <baptiste.coudurier at smartjog.com> writes:

> Hi
> Michael Niedermayer wrote:
>> (not that mpeg-ps/ts and matroska would set codec_tag correctly ...)
> Yes, mpeg-ps should set codec_tag to startcode.

There is no logical value to put there for mpeg-ps.  For mpeg-ts, the
codec ID from the PMT would be a natural, albeit pointless, choice.
The same value is used in the MPEG-PS PSM when present, but since PSM
is optional when only MPEG1/2 video and audio is present, there is no
obvious choice for codec_tag.

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.

I feel sorry for all you people who were raised on AVI files.  I
really do...

M?ns Rullg?rd
mans at mansr.com

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