EffecTV is an extremely fun program for manipulating video in realtime. You need Linux, a supported video capture card, and preferably a video camera (unless you're content to work with whatever's on tv). The mainpage on Sourceforge: effectv.sourceforge.net/index.html and github I recommend getting it off the cvs, rather than the provided links, so try this link: sourceforge.net/projects/effectv/.

It has the capability to be used in post-production, for special effects or more mundane processing, but the main thing is real-time: set it up at a party or large event at put on some groovy psychadelic effects.

There's full OpenGL support, and it's easy to code an effect- BumpGL is something I did in a couple of hours, and it's in the latest BSB release. As is typical with many projects, the interface takes as long or longer than the main program itself...

As these show, the results can be bumpy. A less static filled source would smooth it out some, or processing in-effect.