Definition of M4A, M4B, AAC file extension

M4A: 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.

M4B: Files in .M4B is 100 percent identical to .M4A, but just with different name. So, .m4b is, like .m4a, an audio file wrapped within MPEG-4 container format. The audio encoding can be virtually anything, but most collomly used encoding for both, .m4a and .m4b, files is the AAC.
The only reason for the duplicate naming convention is so that the Apple's iTunes software and iPod players can recognize the file as an audio book rather than a normal audio track and thus allow "bookmarking" the file.

AAC: Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. AAC is promoted as the successor to the MP3 format by MP3's creator, Fraunhofer IIS. AAC's most noted use is as the default audio format of Apple's iPhone, iPod, iTunes, and the it used for all iTunes Store audio (with extensions for proprietary Digital Rights Management (DRM) where used).

How to play M4A, M4B, AAC music in ordinary music player?

Audio books purchased from iTunes are in .M4B format which can only be played on iPod. M4A is identical to M4b. All AAC users must license the technology from the VIA Licensing Corporation. So, these files couldn't be played anywhere, anytime you want. Sometime, we can say these are apple music format.

So you need to convert these music files to ordinary music format such as MP3, WAV or WMA files. Then you could play on any of your computers or devices.

Share DRM Music will do the job for you. You could download it and free try, the trial version of it only have the limitiation that converting 3 minutes of each music files. If you bought the full version, the limitation will unlocked.

Share DRM Music use a virtual CD burner to automate the whole procedure of burning / ripping / encoding all in one. What you need to do is just select the virtual CD burner as the default cd burner in your iTunes, then burn the music file you want to convert to DISC. Share DRM Music will do the rest job for you automatically.