The ffmpeg is cross-platform and very powerful software to handle video/audio or to stream it. On Linux ffmpeg can capture X11 screen with a command below:
ffmpe
http://nerdlogger.com/2011/11/03/stream-your-windows-desktop-using-ffmpeg/
explains how to do it.
basically, install uscreencapture dshow filter, then ffmpeg -f dshow -i video="UScreenCapture" out.mp4