Good interview process. First, I didn't initially apply to Audible but to other Amazon divisions, and my application was forwarded to Audible. They then gave me an online assessment (OA) testing coding abilities (2 questions you have to write functional code for, and for each you also are expected to write in a free response section a description of the code and running time to make sure you didn't just copy something off the web).
In 1-2 business days, they scheduled me for an interview for the next week (4 1-hour long virtual interviews on the same day). My interviews had 3 technical, 5 behavioral parts. Several days before the interview, a recruiter connects with you to prepare you. The coding part (data structures and algorithms, software design) is standard and was not too hard for me, but it's important to prepare responses for Audible's PEOPLE PRINCIPLES. Have at least 2 concrete examples for each principle. I can't stress this enough.
For the interviews, the technical questions were basic OOP, DS/ algorithm questions. Just study things like OOP, arrays, lists, sets, binary trees, graphs, recursion, dynamic programming, etc and you should be fine. You can use whatever language. The behavioral part is something you should definitely come prepared for with written examples, following the instructions of the recruiter.
After the four hour interviews, I got a response within 2 business days stating I received the offer. So this was a short process overall from initial OA to final offer (~2 weeks).