Record video using ffmpeg

Grab the screen and output it

ffmpeg -f x11grab -i :0.0 out.mkv

Play the video

ffplay out.mkv

Specify the resolution if needed along with the audio

ffmpeg -video_size 1366x768 -framerate 25 -f x11grab -i :0.0 -f alsa -ac 2 -i hw:0 out.mkv