Regular audio CDs
Just like any music CD but, of course, 1 book will be span several CD’s. The average book is about 8 CDs but can be much more, as in the case of Shadow Warrior which is 18 CDs.
This is a regular audio CD with mp3 files burned onto it. The mp3’s are processed at 192 kbps and sound every bit as good as the CDs. Most new CD players can play an mp3 CD but you’ll need to make sure. The files can be copied to your computer for listening and/or transferred to your choice of device for mobil playback.
The book is broken up into chapters and those files are converted to mp3’s at 64k. At this bit rate, the books are reasonably sized for download but without noticeable degradation of sound and mp3’s are compatible with all computers and most (if not all) listening devices on the market today.
Based on the size/length of the book, the files are bundled into 1 or more zip archives to make downloading easier. Most computers don’t require any special software to expand a zip archive.
For details about the mp3 format, check out this wikipedia page.
M4b files are specific to audiobooks and they have the ability to contain chapter and other data markers. Audiobooks converted to m4b are generally 1 or 2 files with each file being up to 5 or 6 hours in length. Contained withing the files are the chapter markers and other information like author, narrator, title etc. Supported players will show the chapter markers making it easy to move through the book. Most apple devices support m4b files and there are several android apps like “Smart AudioBook Player” that will support these files.
The sound quality is the same as the mp3 downloads but there are fewer files to manage and pause/resume is more reliable than with mp3’s, at least in my experience.
For details on m4b files, check out this Wikipedia page