[NUT-devel] Fourcc spec

[Måns Rullgård]

Oded Shimon <ods15 at ods15.dyndns.org> writes:

> 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.

This makes no sense at all, but I think you already knew my opinion...

-- 
Måns Rullgård
mru at inprovide.com