Yes you need to provide both an Audio book and an ebook as inputs, if you only have one of these, you could try getting the other from your local library, or you could sail the seas. It’s not a fool proof process, so sometimes you have to try different formats of Audio books to make it work, also depending on how beefy your computer is, it will take some time to process, 1-2 hrs for big books like Stormlight Archive on my laptop