An M4B file contains audio stored in the MPEG-4 format and compressed using AAC encoding. M4B files support book features like chapter breaks and bookmarking. They are nearly identical to .M4A files. Apple copy-protects the M4B files they provide using FairPlay DRM. So M4B files downloaded via iTunes or Apple Books play only on authorized computers and Apple devices, using iTunes or Apple Books.
If you have trouble playing an M4B file, it might be because you are not playing it in iTunes or Apple Books. Or because your device is not authorized to play it. To open an M4B file, download and install iTunes.
You may get a message the file extension might not be recognized. Ignore this and click Yes to play the content. You can also try the VLC media player.
The main issue with MPEG-4 Audio Book Format is that the M4B file wrongly associates with programs. This makes the file open by apps not meant for it. Or shows no associated program. To solve this, first double-click the M4B file icon to open it. If the operating system has a suitable app and association, the file should open.
If it doesn’t open correctly, look for different software to open M4B files. Install it and try again. It is enough to change the extension to .M4A. Files of 771 different types have the M4B extension on various operating systems. The MPEG-4 Audio Book Format file format and TuneClone Audio Converter were developed by Apple.
Apple iTunes
VLC Media Player