Argh - can I change and MP3 into an MP4?

[karolyp]

So, I've started working on DD's 2nd year montage and now onetruemedia only accepts MP4!!! And of course, I had copies of all the songs in MP3 format as that's what they used to accept - argh!!!!!

Is there anything I can do to change the format?

Is Walmart.com's music downloads in MP4 format - if not, any suggestions on where I can I find them???

This is so frustrating.....