So I recently discovered that MP3 files require a license for usage commercially. I want to share this in case other people didn't know this.
For game's it's required that you pay $2,500 in royalties PER title (meaning every game released) after 5,000 copies have been distributed.
Though I wouldn't recommend using mp3 files for game's, I have been looking at other alternatives.
Obviously wav and ogg files are a very good alternative, but so are mp4 files. Specifically m4a/aac files (mp4 is alot more complex than one can think. Just look it up on wikipedia if you want to know about mp4 files). M4a's are much higher quality than mp3's and do not require a license or royalty. Plus, mp3 is getting old... the only reason why it's still alive is because it is still mainstream. m4a's are also higher quality than mp3s at the same bit rate, but higher bit rates mean bigger file sizes.
For more information on mp3 licensing, look here: http://mp3licensing.com/royalty/