Reduce the size of a Avi video

The easiest command I found, is using avconv. To install avconv in Ubuntu, open a terminal (Alt+Ctrl+t) and enter

sudo apt-get install libav-tools

To convert a video from .avi to .mp4, just use

avconv -i InputVideoName.avi outputVideoName.mp4

To change the size of the video you can add the -s flag, e.g.

avconv -i InputVideoName.avi -s 720x540 outputVideoName.mp4