[FFmpeg-devel] [WIP] XComposite window capture demuxer (Linux)

[Marton Balint]

On Tue, 19 May 2020, Lynne wrote:

> May 19, 2020, 09:23 by ema at fastwebnet.it:
>
>> Hi Marton,
>>
>> Thanks very much for the feedback; below answers to your points - let me know further feedback if any.
>>
>>> And sorry, I cannot say how useful this would be, maybe now is the time
>>> for people to speak up if somebody is particularly against adding this
>>> for any reason.
>>>
>>
>> I haven't been able to capture video-games/3d apps running in full screen with x11grab, and when running in windowed mode the capture was sub optimal in terms of quality (lost frames/choppy/etc etc).
>> Unless we have better solutions with ffmpeg/libav* (which I'm not aware of :) this xcompgrab would target such audience (smooth capture alas more CPU usage).
>> But again, if there's already a better capture, then this has been an academic exercise :)
>>
>
> There already is a zero-overhead capture on linux - kmsgrab. It works on AMD and Intel.

As Nicolas mentioned, kmsgrab practically requires root. Also, I tried it 
on Intel half a year ago on Ubuntu 18.04, and it simply does not work 
correctly. There were crashes, there were random failures with cryptic 
error messages, usually at the beginning of the capture, somtimes in the 
middle of it. And the captured frame was missing some of the drawn opengl 
primitives, it looked like kmsgrab grabbed the frame from the back buffer 
and not the front.

So kmsgab on Intel is a no-no for me.

Regards,
Marton