This is a command line utility I wrote to expedite the conversion of my legally purchased Audible books to a more portable format (mp4) and to split them by chapter. I listen to them in Overcast with its Smart Speed functionality.
It requires ffmpeg to be installed on the system. In my case (macOS) it
is available easily via Brew.
This isn't really intended at this point to be polished and generally useful, I just found myself doing these things manually all the time and it was annoying. That said, though, for an experienced developer it should be pretty easy to make this work for you.
Assuming you have python and ffmpeg, you can run this pretty quickly:
yarn install
yarn main
By default it will look for any .aax files in $HOME/Downloads and start
working on them all. You must create a config.json in the root of this
project with at least the activationBytes key set. This is your
encryption key from Audible which you must have already determined by
other means.