[FFmpeg-devel] [PATCH] pthread: Fix ff_thread_get_formatissues when called outside frame decode.

Hendrik Leppkes h.leppkes at gmail.com
Mon Mar 9 15:28:48 CET 2015

On Mon, Mar 9, 2015 at 1:50 PM, Reimar Döffinger
<Reimar.Doeffinger at gmx.de> wrote:
> On 9 March 2015 13:34:24 CET, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
>>On Mon, Mar 9, 2015 at 7:38 AM, Rainer Hochecker
>><fernetmenta at online.de> wrote:
>>> Reimar Döffinger <Reimar.Doeffinger <at> gmx.de> writes:
>>>> Any reason to believe this patch causes it?
>>>> Because I can't see how it would.
>>>> Maybe it's just a bug with DXVA and multithreading in the HEVC code?
>>>> Can you provide some more information like a stacktrace, possibly
>>using a
>>> tool like DrMemory?
>>> I don't think the patch itself is the root cause of the issue, it
>>> triggers it. get_format is called 4 times, something seems to get
>>> in opening our hw decoder.
>>> Do you have an explanation why it works with thread_safe_callbacks
>>set to 1?
>>> I am wondering if hevc misses the multithreading fix done for other
>>> http://ffmpeg.org/pipermail/ffmpeg-cvslog/2013-March/062620.html
>>> What do you think?
>>I build the HEVC HWAccel support, and I consider frame-threading with
>>hwaccel an abomination that should not be supported, so I didn't spend
>>any time thinking about it.
>>Honestly, there are several issues with MT+HWaccel in H264 as well, at
>>least on Intel hardware, so I can only strongly urge everyone to not
>>combine it. There is zero advantages, and only downsides!
> Only if you completely ignore the practical issues that anyone trying to use it will have.
> In many cases applications will not know whether hardware supports decoding the video until there get_format call. Worse, it can even change from supported to not supported.
> Do you expect everyone to disable multithreading "just in case"? Buffer the last n bits of data to be able to restart decoding?

What I do is simply restart decoding with the packet that failed the
hardware decoder. Don't need to buffer anything, you still have the
AVPacket in question anyway.
This allows a perfect and seamless change without requiring the hwaccel-mt hack.

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