MP4 (MPEG-4) files were developed by the Motion Picture Experts Group (MPEG) as a type of compressed file which allows for the seamless online sharing of video and audio files. Unfortunately MP4 audio files are not yet used as universally as MP3 (MPEG-3) files. Therefore you may want to convert your MP4 files on your computer to MP3 files. You can do this easily in iTunes. Tips Writer Bio

How to Convert an MPEG4 to an MP3 on iTunes  7 Steps  - 71