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

[Hendrik Leppkes]

On Thu, Jan 21, 2016 at 1:14 AM, Andreas Cadhalpun
<andreas.cadhalpun at googlemail.com> wrote:
> On 20.01.2016 10:22, Hendrik Leppkes wrote:
>> On Tue, Jan 19, 2016 at 11:54 PM, Andreas Cadhalpun
>>> Can the crashes be reproduced with VLC?
>>> If so, are they reported in the VLC bug tracker?
>>
>> Who knows, I didn't test every single player that uses avcodec.
>> The image corruption on Intel GPUs can certainly be reproduced in any
>> player that uses MT+HWAccel though, so the crashes probably can too,
>> but due to threading the crash is non-deterministic.
>
> I'm still not sure of the scope that this problem has.
>
> If image corruption always happens with MT+HWAccel, why didn't VLC
> change this long ago due to users complaining about that?

I don't know VLC internals, nor do I really use it beyond the occasional test.
All I know is that back in 2014 they disabled MT with DXVA2 on their
end because of just such corruption issues, but they worked around
that somehow and turned it back on later.

http://git.videolan.org/?p=vlc.git;a=commitdiff;h=bf9b995528941436fbdfad6e60ce7af76f20ea2e

Looks like they added extensive locking around everything to prevent
this, which is not something that should be required.

>
> Also, can the crashes be reproduced with the command line tools
> from FFmpeg 2.8?
>

Yes, under some circumstances with DXVA2, but it needs some fancy
files with resolution changes iirc.
No, don't have a reproducable test case handy right now.

- Hendrik