WHAT IS M4B?
MPEG-4 Audiobook File
Apple created the M4B format for playback of audiobooks, radio programs, and podcasts. The main feature that distinguishes the M4B file type is that the files support the use of bookmarks, so the listener can return to a previously defined point. If you’re wondering how to open M4B audio tracks, refer to the associated programs below.
Files with the M4B specifications are exclusively encoded with either lossy AAC or the Apple Lossless codecs. The contents of an M4B file can be protected with DRM (Digital Rights Management). In this case, users will need a corresponding (possibly fee-based) license to play these M4B audio tracks.
iTunes, QuickTime Player, Windows Media Player, and VLC