Files in .M4A format are actually the audio layer of (non-video) MPEG 4 movies. M4A is slated to become the new standard for audio file compression. This format is also known as Apple Lossless, Apple Lossless Encoder, or ALE. It is a new codec designed to provide lossless encoding in less storage space.
try itunes. pwede kasi sa ipod yan. or if not, find a codec for this. usually divx player makakaplay din n2 since it can play mp4.