Sorry for the delay replying, I've been off getting married ;-)
Basically, we're going on a blanket avoidance of copyright/royalty issues by asking people to use creative commons/royalty free imagery and music. So you could find some stock music or create your own. Video should also be original in terms of imagery - live action cosplay/animation/etc rather than Warner Bros film clips.
I hope that answers your query okay. Just reply if not!