We have an article about screen cast with mpeg1 here. Now we are providing a better quality way with VP8.
The command is very similar:
ffmpeg -f x11grab -r 24 -s 1920x1080 -i :0.0 -f pulse -ac 2 -i default -c:v libvpx -b:v 40M -qmin 0 -qmax 0 -deadline realtime -cpu-used -16 -c:a flac -threads 2 output.mkv
There is a few difference:
The -qmin 0 and the -qmax 0 means that we do not use any quantization to compress the video, which means the best quality.
The -deadline realtime means that the vp8 encoder will not have any extra time to do any complicated calculation.
The -cpu-used -16 means that the vp8 encoder will not have any extra cpu capability to do any complicated calculation. (Of course any single computer program needs CPU... That is why we said "extra" for better understanding.)
That is it.
Have fun; be free!