m4a stands for MPEG4 Audio. [explanatory link]
It is the replacement for mp3. It is likely your friend ripped the music under iTunes. You can use a Windows machine or Mac with iTunes or whatever app to convert them. Under Linux you can use dir2ogg for which rpm's can be found [here]
. The link for the rpm is about 1/4 of the way down the page. There are detailed instructions on how to convert the m4a's to wav and/or mp3.