Screen area recorder for Ubuntu - only black screen...

[Bo Berglund]

On Mon, 22 Feb 2021 08:38:30 -0500, Little Girl <littlergirl at gmail.com> wrote:

>Hey there,
>
>Bo Berglund wrote:
>
>>So I tried to use a ready-made Linux recorder "vokoscreen" which can
>>be installed using apt.
>>It seems to have the functions I am after but when recording I am
>>only getting audio, the screen is totally black.
>>I have placed the area selector tool above a Firefox window playing
>>the video and adjusted it to the video area.
>>
>>When I record the selector tool changes by removing all controls
>>inside the video area. So it looks like it is doing what it should.
>>
>>But as I said the resulting mp4 video only contains a black screen,
>>while audio is OK.
>
>I had the same issue, except that my video was green instead of
>black. Try turning off hardware acceleration in Firefox. That solved
>it for me.
>
>https://support.mozilla.org/en-US/kb/upgrade-graphics-drivers-use-hardware-acceleration
>

Thanks, I have turned off acceleration on FireFox now.
But vokoscreen did still not work on the system I am testing it on.
Audio capture is OK but not video....

I also tested a standalone ffmpeg command I found in an internet discussion on
this very matter and it too failed to grab the video but got the audio.
It was purportedly the command used by vokoscreen (however they know that)...

This is how it looks like, I have changed coordinates when running it on the
laptop:

ffmpeg -f x11grab -framerate 25 -video_size 622x484 -i :0+47,339+nomouse -f alsa
-i pulse -pix_fmt yuv420p -c:v libx264 -preset veryfast -c:a libmp3lame -q:v 1
<path-to>/output.mp4

I am assuming here that this defines the area on the screen that should be
captured:
-video_size 622x484 -i :0+47,339+nomouse
where 47,339 is the coordinates of the upper left corner of the capture
rectangle.


-- 
Bo Berglund
Developer in Sweden