Here's a note to explain M4a audio, which is taken from DVD Soft Website
"M4a stands for MPEG 4 Audio, and it is a popular file extension used to represent audio files. Most people are familiar with Mp3 and how it shrinks down the file size of songs and other audio files. M4a and Mp4a do the same thing as Mp3 does, but even better. Quality is better and file sizes are usually smaller than Mp3 files."
Mp3 and Mp4a are both compatible and will play on all devices.