[FFmpeg-devel] [PATCH] avcodec: only warn about hwaccel with frame threads

[Hendrik Leppkes]

On Sat, Jan 23, 2016 at 2:38 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
> Hi,
>
> On Sat, Jan 23, 2016 at 8:28 AM, wm4 <nfxjfg at googlemail.com> wrote:
>
>> On Sat, 23 Jan 2016 13:50:32 +0100
>> Michael Niedermayer <michael at niedermayer.cc> wrote:
>>
>> > On Sat, Jan 23, 2016 at 11:42:54AM +0100, Hendrik Leppkes wrote:
>> > > On Sat, Jan 23, 2016 at 10:12 AM, Andreas Cadhalpun
>> > > <andreas.cadhalpun at googlemail.com> wrote:
>> > > > VLC uses hwaccel with frame threads and it works fine, but returning
>> > > > an error here made it fail.
>> > > >
>> > > > This regression was introduced in commit 31741ae.
>> > > >
>> > >
>> > > I'm still opposed to this, and so is everyone else that commented on
>> the issue.
>> >
>> > I have no oppinion on the patch itself but i think
>> > if MT+HWaccel works in some case(s) and is faster then there should be
>> > a way to enable that. We have optional "fast" decoding support too
>> > that skips some checks and could crash or uses simpler dequantization
>> > or our skip loopfilter support, ...
>>
>> Whether it's faster is an entirely different question.
>>
>> The problem is that we don't want to enable hwaccel with MT because
>> it's much pain for little gain, but then if fallback to software
>> happens, decoding will remain single-threaded.
>>
>> Possible solutions:
>> - somehow allow changing the number of frame threading threads during
>>   fallback
>> - add a wrapper codec, which behaves like the old one, but reopens the
>>   codec behind the scenes in order to change the number of threads on
>>   fallback
>> - making sure hwaccels actually work with MT (complicated => not worth
>>   the trouble)
>
>
> Why don't we ignore threading (set active_thread_type to NONE) if hwaccel
> is enabled? Doesn't that fix everything in one single place?
>

Threading is already setup and running when the hwaccel gets
activated, and its not designed to go in and out of threading mode at
will.