[FFmpeg-devel] [PATCH][RFC] avcodec: disallow hwaccel with frame threads

[Andy Furniss]

Hendrik Leppkes wrote:

>>> I do not agree that it should be a warning. As outlined in the
>>> commit message and this thread, there are serious flaws with
>>> frame threading and hwaccel.
>>
>> I'm fine with it being an error, but since it is an API change, it
>> should follow the usual deprecation period to allow downstream
>> users time to fix it. Meanwhile it can be a warning so that people
>> notice the problem.
>
> Its fundamentally broken, and making it a warning would re-introduce
> known crashes. So no.

So are the flaws in ffmpeg or particular drivers?

It does seem a shame perf wise, I've been testing my AMD UVD decode
recently and for 500 UHD frames in a really high bitrate h264 file it's
like -

ffmpeg threaded = 16 sec.

ffmpeg single thread = 20 sec.

gstreamer vaapi 14 sec.

gstreamer omx 10 sec.

the omx is a faster as the others do nv12 -> I420 on cpu (AFAICT)

Maybe -threads 1 hurts perf by limiting the format conversion as well?

Is there a way to get whatever the h/w spits out (nv12) directly? Trying
to ask for nv12 seemed to get a double conversion.