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

[Andreas Cadhalpun]

On 21.01.2016 23:56, Hendrik Leppkes wrote:
> On Thu, Jan 21, 2016 at 8:36 PM, Andreas Cadhalpun
> <andreas.cadhalpun at googlemail.com> wrote:
>> On 21.01.2016 02:10, Hendrik Leppkes wrote:
>>> Looks like they added extensive locking around everything to prevent
>>> this, which is not something that should be required.
[...]
>>> No, don't have a reproducable test case handy right now.
>>
>> If it's so difficult to reproduce any kind of problem caused by this
>> combination I'm not sure why you insist on erroring out.
> 
> Just because an error is rare, we should leave it in? What kind of bug
> squishing concept is that?

No, you misunderstood me.
The real problem happens rarely, but the error is always returned.
So on one hand returning this error prevents rare problems, when the
API is (mis)used, but on the other hand it breaks the use case of VLC,
which, as you say, prevents the real problem by extensive locking.

So returning this error breaks more than it fixes.

>> Also you only mention DXVA2 now, but the error is also returned for
>> VDPAU and VA-API. Are they also affected by these potential problems?
> 
> I would assume thread safety might be an issue for all of them. Our
> VA-API maintainer signed off on the patch in any case.

So it seems to be a theoretical problem for them, but still the error
is returned. That doesn't seem correct.

>> All in all it seems to me that the collateral damage caused by returning
>> the error outweighs it's value.
> 
> I disagree, and apparently so did the others that OK'ed the patch.

When this patch got OK'ed at least I wasn't aware of it's implications.

> On top of all that, not even the player in question seems to care,
> otherwise we might have gotten at least one official comment or
> question from them, but alas, silence.

I do care about this, however.

Best regards,
Andreas