Gephex

Gephex is a modular video jockey software. The base visuals can be chosen from sources like video files or cameras.
Then they can be modified by filters and mixers. Each modifier has several parameters, that can be controlled by signal-generators, input devices like joysticks, sound cards, or midi-devices.
Gephex runs on Win32, GNU/Linux, FreeBSD and Mac OS X. The effect engine is independent from the user interface, which can be de- and attached at runtime. All effects and media streams are extendible by plugins. Gephex is written in C++.
Here are some key features of "Gephex":
· Free (GPL) and cross-platform (GNU/Linux, Win32, experimental Mac OS X support)
· Graphical user interface (written in QT)
· Easily extensible with plugins
· Client server architecture
· Support for video files (ffmpeg, libavifile, video for windows, directshow)
· Ports of most EffecTV effects
· Vloopback support (input and output)
· Webcam and tv card support (v4l and directshow)
· Midi/joystick input support
· Audio support (capturing from soundcard, simple beat detection, simple mixing, audio synthesis, audio output)
· Frei0r plugin support