[NUT-devel] Fourcc spec

[Oded Shimon]

On Sat, Dec 23, 2006 at 03:09:24PM +0200, Oded Shimon wrote:
> On Sat, Dec 23, 2006 at 01:56:29PM +0100, Michael Niedermayer wrote:
> > if the lists are not normative that i bet every commercial company will
> > use their own fourcc divx, 3ivx, ...
> > why?
> > 1. the company can better claim that its their own supperior technology
> > 2. they dont need to bother to implement the standard correctly, its enough
> >    if their decoder matches their encoder, this is what has happened with
> >    codecs in avi and as its less work = less money it will happen again.
> >    It didnt happen with mpeg-ps/ts just because there are too many hw
> >    decoders around which cant be updated that easily all IMHO
> > 
> > if my hypothesis turns out to be true then 3. would loose the 
> > "single fourcc per codec" and ""Sane" codec names" as in practice the
> > majority of videos would not use the recommanded fourccs
> > 
> > so that brings us to option 4 which would require a player to only support
> > a codec if the one and only standard fourcc where used, if a unknown fourcc
> > is used demuxing it would be a violation of the spec ...
> > 
> > if that would prevent the issue iam not sure though ...
> 
> The list IS normative for demuxers, not for muxers. This was already in my 
> original proposal, I forgot to re-mention it here.

To spell it out again:

A muxer SHOULD use the fourcc from the codec list
A demuxer MUST support the fourcc from the codec list if it supports the 
codec at all

Which means demuxers can have additional fourcc's to the ones in the 
official list, and a muxer can do whatever it wants. But obviously, both 
are better off using the official list.

- ods15