I recently made a couple of promo videos for someone using my Nikon D7000...but I'm curious how to get them into a more universal format that any player will play?
Yes, Handbrake will do it without a problem. It is open source, free, and available for OS X/Windows/Linux. It works like a champ. I have been using it on my MacBook Pro and on my Ubuntu Linux laptop for a couple of years now. I highly recommend it.