Video of a tiny demo

Use ffmpeg to screencast in ubuntu. Here is a command to capture lossless mkv:
ffmpeg -f alsa -ac 2 -i pulse -f x11grab -r 30 -s 1024x768 -i :0.0+4,400 -acodec pcm_s16le -vcodec libx264 -vpre lossless_ultrafast -threads 0 output.mkv