How can I change an iTunes song & video file format into an MP3 song & video file format?

I believe the iTunes are .m4p and .m4v but I need them to work on my MP3 player, and it only reads .mp3, .avi, .txt, .mpeg, and a few others. What should I change the file format to so they will work?How can I change an iTunes song %26amp; video file format into an MP3 song %26amp; video file format?try this (link in source)