If the Matroska format is used, in certain framerates it doesn't record at exact input framerate, but rather at a little higher than the input framerate.
As an example:
ffmpeg -video_size 1920x1080 -f x11grab -framerate 30 -i :0.0 -c:v libx264rgb -crf 0 -preset ultrafast video.mkv
doesn't generate a recording at 30fps, but rather at 30.0003fps.
This is not good, because even a slight change in input framerate can cause major frame stutter. Unless ffmpeg is speeding up the stream by 1.00001x, which I don't think so when using x11grab.
To prove this, VLC can be used for checking the frame rate.
Is there any way to force exactly 30fps, or is this a format flaw?
Linux linux 4.1.15-rt17-1-rt-fixedtimers #1 SMP PREEMPT RT Sat Jan 16 01:14:52 GMT+5 2016 x86_64 GNU/Linux