m4a is the default unprotected file format for iTunes
An Explanation from Wikipedia (why write when I can cut and paste?)
.MP4 versus .M4A
M4A stands for MPEG 4 Audio and is a filename extension used to represent audio files.
The existence of two different filename extensions, .MP4 and .M4A, for naming audio-only MP4 files has been a source of confusion among users and multimedia playback software. Some file managers, such as Windows Explorer, look up the media type and associated applications of a file based on its filename extension. But since MPEG-4 Part 14 is a container format, MPEG-4 files may contain any number of audio, video, and even subtitle streams, making it impossible to determine the type of streams in an MPEG-4 file based on its filename extension alone. In response, Apple Inc. started using and popularizing the .m4a filename extension, which is used for MP4 containers with audio data in the Advanced Audio Coding (AAC) or its own Apple Lossless (ALE, ALAC) formats. Software capable of audio/video playback should recognize files with either .m4a or .mp4 filename extensions, as would be expected, since there are no file format differences between the two. Most software capable of creating MPEG-4 audio will allow the user to choose the filename extension of the created MPEG-4 files.
You can read the entire wikipedia page at
Many people think iTunes audio is "aac" but I've never actually seen an .aac file extension on a file.
m4a and m4p often...