ffmpeg \
-f x11grab -video_size 1280x720 -framerate 30 -show_region 1 -i :0.0+0,49 \
-f v4l2 -video_size 640x420 -framerate 30 -i /dev/video0 \
-lavfi "[0:0] [1:0] overlay=main_w-overlay_w:main_h-overlay_h" \
-f flv test.flv