That stuff was shot in the studio, and it was video feedback. If you're talking about the gloopy-looking colored & animated backgrounds that showed up behind a band, that was done with colored water, colored oil and a couple of clear-glass plates mooshed around.
"Gloopy" and "mooshed" are both highly-technical terms.
Thanks Dave. So are there any methods to simulate video feedback using After Effects that you're aware of?
Thanks a lot - knowing the correct search term is half the battle.
Video Feedback is real time. A camera shoots a monitor, which the camera is feeding. If there's a switcher involved, you can add things over the camera input: a person chroma-keyed, for instance.
I don't know of any good way to replicate the look in AE.