Allow downscaling resolution of video recording

[maximbaz]

When I record my 4k screen to video4linux2, wf-recorder uses 100% CPU. I want to record full screen, but I'm willing to sacrifice resolution, and record it in Full HD, if that helps reducing CPU usage. If I record a part of the screen of 1920x1200 resolution, wf-recorder only consumes ~25% CPU. I'd like to be able to tell wf-recorder to record full screen but downscale it to Full HD, so that hopefully CPU usage is not that high.

[ammen99]

I think you are already aware of https://github.com/schauveau/wf-recorder-x. I do not know why the person who wrote that code there hasn't opened PRs to merge his work.

@schauveau Any plans for bringing your work to upstream?

[maximbaz]

Yes, I wanted to try that project but sadly it was forked before streaming to v4l2loopback was implemented, and quick attempt to rebase on master failed with some conflicts (I didn't loop much into it).

[ammen99]

One workaround is to just lower the resolution of your screen. I know this isn't ideal but since you're already sacrificing on quality ...

[maximbaz]

Good point, and this reduced CPU usage to 50%

[varac]

@ammen99: Can you think of any other possible CPU load improvement besides reducing screen resolution ?

[soreau]

@varac You can use the gpu to encode the video using vaapi. Refer to the README for more information.

[truesilver92]

If we change the scope of the project to just being an ffmpeg input device then you will already have this capability as an ffmpeg filter #139

[hholst80]

In case anyone runs across this issue the solution is this (no need to use the fork):

Suppose i have a 4k source and want to save the recording in full 1080p:

wf-recorder -f test-vaapi.mp4 -c h264_vaapi -a -F scale_vaapi=format=nv12:w=1920:h=1080