Create list of posts with ".mp3" or "youtube / vimeo" with post indexer?

I’m looking keep a list of those posts that actually have an mp3 linked, and those that have either vimeo or youtube embeded.

I can make changes to the post process to "register" a post in a table if it meets either of these conditions, or I can parse all posts and find them (ala post indexer).

I’d prefer to not use tags because some users may tag a post, for instance, about mp3 but not actually having an mp3 — I suppose a filter on the output could work as well.

Would the post indexer work for this? Whats the best solution to do this across all MU blogs?

My use case will be a "playlist".