To encode your video in a free codec (ie not proprietary), use Theora from Xiph.org. This codec is still in ALPHA stage (as in, not even beta!) so don’t use it for mission critical stuff just yet. However, xine and mplayer already play the codec. If you try to convert an avi to theora (using ffmpeg2theora) the audio will be out of sync with the video. So either encode the original video as an mpeg or type in the following: