[FFmpeg-devel] [PATCH] avformat/movenc: Always look up mov tag for AV1.

[James Almer]

On 8/13/2018 7:47 PM, Carl Eugen Hoyos wrote:
> 2018-08-14 0:36 GMT+02:00, Thomas Daede <bztdlinux at gmail.com>:
>> On 08/13/2018 03:30 PM, Carl Eugen Hoyos wrote:
>>> Why isn't av1 added like the existing codecs?
>>
>> That would generate invalid AV1 files if -strict -1 or -2 specified
> 
> That is the idea of -1 and -2.
> 
>> (and currently AV1 mov writing is behind -2).
> 
> Is the specification still unfinished?

Yes.

> Then what is the exact purpose of this patch?

The issue at hand is that when remuxing from ivf, the propagated codec
tag AV01 is written as is instead of the correct av01 (as listed in
ff_codec_movvideo_tags and codec_mp4_tags) because a case insensitive
check takes place in either ffmpeg.c or libavformat generic code (i
don't recall exactly where), which of course assumes av01 == AV01.
The latter is only correct for ivf, not mp4.

If this patch adds the AV1 codec id inside the "s->strict_std_compliance
>= FF_COMPLIANCE_NORMAL" check as you suggest, and a muxing process is
done with -strict experimental, then the wrong codec_tag will be written.

An alternative would be to change the aforementioned case insensitive
check into a case sensitive one, but that could break some other
scenarios as i presume it was made that way for a reason.