The video-conversion tag covers software & formats related to converting videos from one format or container to the other.
The Super User blog has an entry about Video Conversion done right: Codecs and Software, which covers basics of video conversion tools.
Tools and Tags
- Handbrake, see also handbrake
- MPlayer and Mencoder, see also mplayer and mencoder, in combination with MeGUI
- VLC, see also vlc
For OS X: