Audible books are often very nice, but there is a fundamental problem with them, they are hard if not impossible to back up and transfer to new devices. While it seems unlikely that Audible is going to disappear, it is not impossible that you might get locked out of your account, or some other set of unfortunate circumstances.

Required Software⌗

Setup⌗

Use either audible-activator or the rainbowcrack tables to get your authcode

Save your authcode to a text file located at ~/.authcode or some other location that you remember

Get ffmpeg installed. For Macs use Homebrew, for Windows use either WSL or ffmpeg’s Windows installation instructions

If on Mac and using Hazel, setup automatic decryption when a audiobook is downloaded

Hazel in settings
Open Hazel's settings in System Preferences
Hazel in settings
Create a new automation rule
Hazel in settings
Make it match the following screenshot
Hazel in settings
Fill in the embedded script, text below
ffmpeg -activation_bytes $(cat ~/.authcode) -i $1 -c copy ~/Audiobooks/$(basename $1 .aax).m4b

This assumes you want to put the files in ~/Audiobooks after conversion, tweak as desired.

Process⌗

Download the file from Audible

If you are using Hazel, you are done

Open terminal

Navigate to your downloads folder

Type the following command into the terminal, substituting the actual file name and desired output location

ffmpeg -activation_bytes $(cat ~/.authcode) -i inputfile.aax -c copy outputpath.m4b