[Ffmpeg-devel] 4XM audio codec_tag

[Michael Niedermayer]

Hi

On Mon, Nov 06, 2006 at 02:55:15PM +0100, Baptiste Coudurier wrote:
> Michael Niedermayer wrote:
> > Hi
> > 
> > On Mon, Nov 06, 2006 at 12:17:20PM +0100, Baptiste Coudurier wrote:
> >> Hi
> >>
> >> Michael Niedermayer wrote:
> >>>>> [...]
> >>>>> if you wish to prevent the user from doing things (s)he wants to do
> >>>>> then you shouldnt write open source software
> >>>> That doesn't mean we should make it easier for users to do stupid
> >>>> things, like creating files in violation of the standards.  Of course
> >>>> we can't completely stop them from doing it, but they should at least
> >>>> have to put some effort into it.
> >>> could you point me to the spec which disallows a new codec to be stored in
> >>> it? iam not even sure if mpeg-ps/ts do that and if they do, are really all
> >>> the things various _different_ standard comittees put in it valid?
> >>>
> >> Depends on container, but I know for sure that ISO Media and derivates
> >> does not support it by defining really constrained specs. (mp4 only
> >> allows 'mp4v' and 'avc1' as fourcc and defines codec type in object type
> >> id, all values are defined or reserved, same for 3gp, I don't really
> >> know for mov, I did not check deeply). I think that overriding a
> >> reserved value is non standard and therefore forbidden.
> > 
> > so to summarize, iso mp4 supports mpeg4video and h264, 3gp which is
> > not mp4 is copy and pasted from mp4 with the table of alowed codec
> > ids edited to support another set of codecs? (no iam not sure, the
> > mp4 systems spec is so fragmented over various documents that i simply
> > cant make sense of it,i dont even know which documents i should look
> > at)
> 
> mp4 also supports jpeg2000, png, mpeg2video, they all have a specific
> object type id in esds (mp4ra.org), non defined values for object type
> id are reserved, therefore forbidden, and I saw vorbis in mp4 using a
> reserved object type id which after was defined for qclp, ouch. That's
> why doing that is really really not a good idea.

using simple numbers is what causes this primarly, using 4 ascii letters
which are related to the codec name makes these things alot rarer
(MS total stupidity in selecting mp4s is the only? exception)

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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