[NUT-devel] Fourcc spec

[Måns Rullgård]

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

> On Sat, Dec 23, 2006 at 09:13:59PM +0000, M?ns Rullg?rd wrote:
>> 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...
>
> Actually, no, I'm confused by your reply...
> I was slightly off - the demuxer is better off using as many fourcc's as 
> it wants, but it MUST include also the official list. The muxer, in most 
> cases, is better off using only fourcc's from the official list, so it has 
> garuntee of demuxers supporting it. I fail to see how this does not make 
> sense. I don't know if you noticed, but I'm going through this entire 
> thing only because of you, I personally do not care. So please, present 
> your arguments.

Having a list makes no sense unless it's normative for both sides.

> In the case of a company _intentionally_ not using an official fourcc, 
> then I don't really care, because if they are doing it intentionally they 
> will always do it regardless of what we ask. (Even if we say MPEG-4 ASP 
> MUST have this fourcc, they can claim their codec is something 
> else/superior and has another fourcc)

You obviously can't stop people violating the spec.  It's not a law,
after all.

-- 
Måns Rullgård
mru at inprovide.com