Although VLC can perfectly hanlde .m4b audiobook files, I usually prefer to split them to mp3 in a way that each mp3 file is one chapter of the audiobook.
If you want to do do the same, I highly suggest you to use m4b-tool. You can download the .phar file from the GitHub releases page.
This really nice tool requires php, ffmpeg and mp4v2.
In order to install them in Archlinux, I gave the following command:
pacman -S php ffmpeg libmp4v2
Now, let’s assume that you have a file named audiobook.m4b and you want to split it. All you have to do is give the following command:
php m4b-tool.phar split --audio-format mp3 --audio-bitrate 96k --audio-channels 1 --audio-samplerate 44100 /path/to/audiobook.m4b
The resulting mp3 files will be placed under a new directory named audiobook_splitted, on the same location with the **.m4b ** file, while each file name will be based on the following template:
001-This is the first Chapter.mp3