Dear All,
I think, for many people, simply collecting the movies that are currently chosen in the media players would be a decent solution; that's because a lot of video designers for theater are not interactively choosing movies by changing the 'movie' input of the Movie Player, 'picture' input of the Picture Player, etc.. For those choosing clips interactively (especially, for instance, using a Random actor) there really isn't any way to be sure that all the necessary media would be included. I guess that, if any movie player has a link to the 'movie input', a warning would need to be generated indicating that the collected media may not include all of the required media.
Best Wishes,
Mark