[FFmpeg-devel] [PATCH]lavf/matroska: Support codec id V_FFV1 for FFV1.

[Dave Rice]

> On Mar 2, 2017, at 9:59 AM, James Almer <jamrial at gmail.com> wrote:
> 
> On 3/2/2017 11:47 AM, Tobias Rapp wrote:
>> On 02.03.2017 15:22, James Almer wrote:
>>> On 3/2/2017 6:28 AM, Nicolas George wrote:
>>>> Le primidi 11 ventôse, an CCXXV, James Almer a écrit :
>>>>> Ah, i see there's generic code to read and write CodecPrivate elements
>>>>> to and from raw extradata for native codecids where no special handling
>>>>> is required.
>>>>> 
>>>>> In any case, the spec says
>>>>> 
>>>>> "For FFV1 versions 2 or less, Private Data SHOULD NOT be written."
>>>>> 
>>>>> The ffv1 encoder creates extradata for v2 and newer, so the muxer
>>>>> should have a custom case for ffv1 in order to detect v2 streams and
>>>>> avoid writing said extradata.
>>>> 
>>>> I have not looked myself at the situation, I only read what you wrote
>>>> her. According to it, it seems here the FFV1 encoder is violating the
>>>> specification and needs to be fixed.
>>> 
>>> I can't say if the encoder exporting extradata for version 2 is right or
>>> wrong, as muxers or bsfs could still use it for whatever reason, but at
>>> least according to the draft ffv1 spec by Michael, it's to be stored at
>>> the container level *only* on versions 3 and above.
>>> https://tools.ietf.org/html/draft-niedermayer-cellar-ffv1-01#section-4.1
>> 
>> The IETF draft explicitly excludes to specify FFV1 version 2:
>> https://tools.ietf.org/html/draft-niedermayer-cellar-ffv1-01#section-4.8.1
>> 
>> IIRC there have been some edits to remove references to version 2 in the IETF draft. In the older document at http://www.ffmpeg.org/%7Emichael/ffv1.html#configuration-record the section contains "version >= 2".
>> 
>> Regards,
>> Tobias
> 
> Well, that makes things a bit more complex.
> Maybe the Matroska spec should follow and also avoid mentioning v2?
> That way we could just pretend those files don't exist and not bother
> trying to drop their extradata during muxing.

I agree. In the FFV1 spec, it is careful to say that it intentionally does not describe FFV1 version 2. I will submit a patch to the Matroska specification to avoid using relative language based on version 2.
Dave Rice