Woah, what system did you find? Sounds way simpler than what I’ve figured out. I’ve read posts about capturing traffic from the network tab of the web inspector but I got really mixed results. That does work, but it was enough of a pain that I explored other options.

The system I eventually found was on Android Libby store files from audiobook unencrypted. They try to hide them by splitting books up into lots of files with random names and distributing them across random folders within its data folder. It even includes some junk folders and files to try and throw you off. None of these files have files types/extensions and Libby tacks on .mp3 when it comes time to play them.

How this can be exploited: I have an android device but this can also be done with Windows Subsystem for Android, or really any other android emulator. I have targeted the parent folder to all that with Syncthing and set it as a one way sync. This way whenever audiobook files are added they are copied to one of my other devices and because it’s one way sync when my loan expires those files disappear from the Android instance, but persist on the device I’ve copied them to. Next step is filtering out all the junk files. This is shockingly easy as I just click into the windows file browser search bar and hit enter. This serves to show a list of any file of any name of any type in all sub folders. Then I just sort the results by size. Libby doesn’t bother to make the junk files the same size as the “mp3s” (remember they don’t say .mp3 yet) so it’s easy to just truncate the list when the files stop being in the kilobytes and start being megabytes.

What’s left is a list of file that want to be .mp3. I use a command line based batch renaming tool to add all the endings, and then begins the painful task of listening to each file to find where in the book it’s supposed to go. The splits do not line up with chapters, so it’s sometimes handy to have an ebook copy to search for phrases. I put them in order then load them all into audacity, merge and then use the detect silence tool set to between 2 and 4 seconds to try and detect the chapter breaks. I’ll manually clean up any misplaced breaks, export as individual files and then finally use one of the many audiobook binding tools out there to bundle it all back together. Though I mostly do that when I’m sharing the book with others. My préférée audiobook listening platform tales individual files very nicely, so I can save a step if it’s only for myself.