[vlc-devel] [PATCH] video_output: wait half the extra time we have without getting the display_lock

[Steve Lhomme]

On 2021-02-22 11:16, Rémi Denis-Courmont wrote:
> Le maanantaina 22. helmikuuta 2021, 9.46.46 EET Steve Lhomme a écrit :
>>>> There's a very simple scenario to support this behaviour. Pause the
>>>> video and change the user filters from the UI. The render changes. It's
>>>> done on the same "pre-rendered" (deinterlace+convert) picture.
>>>
>>> That's still an exception within an exception. It's very seldom that
>>> somebody changes filter settings while paused. In the first place, most
>>> people don't use filters, and most filters mostly don't work anymore due
>>> to hardware acceleration.
>>>
>>> And besides, then what? How is this any different from audio, where we do
>>
>> You can pause video and still see the rendered result.
> (...)
>> None of
>> that is possible in audio. So let's not compare apples and pears.
> 
> You're the one bringing pause which has nothing to do with putting multiple
> samples in the rendering pipeline, and the problem of the filter setting
> latency. Those last two issues do affect both audio and video.

Yes, I'm giving a very concrete example of why audio and video cannot be 
compared when it comes to rendering. Pause is totally different there.

 From what I understood of what you said about audio, the latency of 
filters must be bad on the audio side as well.

Given these 2 paragraphs, I don't think audio is the golden standard we 
should look into to fix video issues.


>>> process samples ahead of time (subject to low latency setting) rather than
>>> at the last minute? You're just confusing latency and frame period here.
>>>
>>> In most cases, latency can be larger than a period. In fact, some filters
>>> do require it (if they need to look ahead) already now. The general idea
>>> that we need to support multiple prepared pictures was already agreed at
>>> the workshop anyway, AFAIR.
>>
>> I don't remember that at all.
> 
> If Alexandre remembers it, it's not just me.

"I don't think we agreed to support multiple prepared picture.
We did discuss the display prepare/display lifecycle and even
mentionned a prepare/display/unprepare construction but I'm
not sure what else we discussed."

One of us is not reading this correctly.