[Ffmpeg-devel] 4XM audio codec_tag

[Måns Rullgård]

Michael Niedermayer said:
> Hi
>
> On Mon, Nov 06, 2006 at 12:17:20PM +0100, Baptiste Coudurier wrote:
> [...]
>>
>> >>>>>>> I would tend towards: better clutter the table a bit and support more
>> >>>>>>> formats however rare than having a cleaner table.
>> >>>>>> Again you've drifted from the question of sharing the codec ID table
>> >>>>>> between unrelated formats, and treating the RIFF table as some kind of
>> >>>>>> absolute reference.
>> >>>>>>
>> >>>>>> Just face the facts: formats use different tags to identify codecs, no
>> >>>>>> matter how much you pretend that all of them use the RIFF values.  The
>> >>>>>> only way to properly handle this is by using one codec tag table per
>> >>>>>> format.  End of story.
>> >>>>> i have no problem with one table per format, what i have a problem with
>> >>>>> is that libav* would fail decoding a file if no match is found and that
>> >>>>> it would leave the codec tag decission to the end user and not suggest
>> >>>>> a default one if theres none in the one table for the target format
>> >>>>>
>> >>>>> if OTOH there is one table per format and a default fallback table then
>> >>>>> thats something different with which iam fine
>> >>>> A "fallback table" doesn't make any sense at all.  None.  Zero.  Nil.
>> >>>> Either a format supports some particular codec, in which case its ID
>> >>>> table will have an entry for that codec, or the codec is not
>> >>>> supported, in which case failure is the only sensible option.
>> >>>> "Suggesting" to use a tag from some other random format instead is
>> >>>> utterly senseless.  Such behavior is what created the AVI mess in the
>> >>>> first place.
>> >>> avi is a generic container its supposed to be possible to store anything
>> >>> in it (with a few exceptions)
>> >>> the same is the case for mov, matroska and nut
>> >>> there is nothing messy with that
>> >> There is nothing messy about a container that can potentially be used
>> >> with any codec.  The mess comes when people INSIST ON INVENTING THEIR
>> >> OWN CODEC TAGS.  How the f*ck are others supposed to know what those
>> >> tags mean if they are not included in some kind of official list?
>> >
>> > uhm, look in the lists for avi and mov? and just read the tag, ohh well
>> > is it so hard to guess that mpg1 is mpeg-1 video?
>> >
>>
>> Now look at 'mp4s', we have to deal with avi fourcc cause someone stupid
>> thought that putting avi fourcc was ok to do...
>
> is that is the worst you can find?
> mp4s is microsofts official fourcc for iso mpeg4 version 1 IIRC
> so i would suspect that this is besides m4s2 the most official fourcc
> for mpeg4 in avi
> really not a good example for bad user invented tags in avi ...

That's not what Baptiste said either.  The problem is people using this AVI
tag in mp4 files, where it is wrong.  AVI and mp4 use different tags for MPEG4
video.

BTW, doing an ffmpeg -vcodec copy of h.264 from mp4 to AVI creates a file
that ffmpeg/ffplay can't decode.  Somehow the same file plays fine with
tcvp's native AVI demuxer.

-- 
M?ns Rullg?rd
mru at inprovide.com