A few things to consider, again, not a legal expert:

Better Situations:
-You are not making a profit with the media in question
-You are not distributing without solicitation
-You are not giving 'easy access' to reproduce the media
-You are limiting distribution to interested parties only (portfolio, applications)

Bad Situations:
-You distribute the media actively
-You charge money in order to make revenue


Other things:
It is becoming a common understanding that sometimes 'sharing' media in a controlled environment online is similar to sharing media in your own home. If your website is private, it's as private as your own living room. Watching a movie with your 8 friends in the basement, for instance, is becoming similar to showing a music clip to your 8 friends online, when it's a controlled environment... meaning, the media (music, video, game, anything) is not being reproduced.


Again, I'm not a legal expert, but I believe my suggestions help you avoid criminal prosecution. Unfortunately, if you contact larger companies about using a video clip to write music over top of, they're likely to just ignore you. When you start making money off someone else's work, then it becomes a big deal.

Ask yourself, if you were the owner of the media you're going to utilize, would you feel like you lost money if you ripped yourself off?