[Ffmpeg-devel] 4XM audio codec_tag

[Baptiste Coudurier]

Michael Niedermayer wrote:
> 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 ...
> 

No, one day, someone put avi fourcc in mov, now we want to decode files
using avi fourcc, then we have to check against avi fourcc in mov, and
then collision appear.

Now same guy thinks, yes, mov is generic container so I can put whatever
fourcc I want, let's put mp4s... and we are in deep shit, He might not
want it all in fact, he just stream copied, and since we honor codec_tag
first, and after all we just cannot refuse him to do that, since mov is
generic container.

Now if you want to prevent any fourcc to be misused in every container,
simply follow standard and refuses to use something non defined. After
all, are we ok to use some non defined C behaviour ?

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
SMARTJOG S.A.                                    http://www.smartjog.com
Key fingerprint                 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
Phone: +33 1 49966312