Believe it or not, it is quite difficult to display a video which you host yourself (that is, not inheriting its display from somewhere else). That is, it is difficult if you want to do it well and clean (using only open source throughout and HTML5 protocol).
If you use. In our case, we currently use MediawikiPlayer which relies on longtail video, which is at least partly open source.
To convert avi to mp4:
mencoder input.avi -o output.mp4 -oac copy -ovc lavc -lavcopts vcodec=mpeg1video -of mpeg ffmpeg -i infile.avi youroutput.mp4
https://superuser.com/questions/848584/convert-avi-file-to-mp4-in-linux