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

[Baptiste Coudurier]

M?ns Rullg?rd wrote:
> 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.

Well atm decoder is considering extradata presence (and some bits) as a
meaning of bistream formating (h264), dunno if it's really better.

I could decide to use 'f264' as 'stsd' fourcc in mov, and use annex b
bitstream formating or another one without nal escaping for example, tag
would be different from 'avc1', and a way to differentiate formatting,
after all mov is a generic container.

It's IMHO wether only codec_tag is sufficient to identify a formating,
or pair codec_tag/container info is needed.

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

Im not an avi fan either ;)

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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