It seems like universally, everyone mixes geometric animations, computer generated music visualizations, and occasionally, video of someone dancing. While this is very clean looking and is easy to match to the music and lighting, I prefer to use actual video and or cartoons, anime, music videos, etc.
I understand there are concerns of copyright. But when you're matching it to the music, blending it with other video, morphing it, does it not fall under the same fair use laws that protect DJs when they sample audio from commercial sources?
Are there other reasons you don't use regular video? Technical or visual considerations? Dictation by venue?