$cat ~/bin/ffmpeg_grab_desktop.sh
    #!/bin/bash

    size=${1:-"1920x1080"}
    offset=${2:-"0,0"}
    name=${3:-"video"}

    ffmpeg -video_size $size -framerate 25 -f x11grab -i :0.0+$offset -c:v libx264 -crf 0 -preset ultrafast "$name.mkv"
    ffmpeg -i "$name.mkv" -movflags faststart -pix_fmt yuv420p "$name.mp4"