Veejay is a ‘visual’ instrument and realtime video sampler

“It allows you to “play” the video like you would play a piano.
While playing, you can record the resulting video directly to disk (video
sampling)”

Veejay can be used to manipulate video in a realtime environment i.e.
‘VeeJay’ for visual performances or for (automated) interactive video
installations.

http://veejay.dyne.org/