How does Audible's .aa file format work?

Question

When I download an audiobook from Audible, I get a bookname.aa file. When I open it with iTunes, iTunes shows me an authentication prompt where I need to enter my audible credentials. I presume the same goes for other media players. Is this some kind of file standard, or did audible have to work with all kinds of media player vendors to support their DRM?

Answer 1

The best information I could find is in this article: and this wiki entry on MultiediaWiki.

doesn't talk about implementation, but after reading this article I'm pretty sure each player has to authenticate with audible.com to decrypt the content.

To quote the article:

How Audible Files Are Protected and Its Restrictions

To prevent the unauthorized copying and playing of downloaded audiobooks, the Audible format uses an encryption algorithm (generically referred to as DRM copy protection).

Interestingly, the actual sound data inside an Audible file is encoded in an unprotected format (either MP3 or ACELP) but is then wrapped up in the encrypted Audible container.

edit: added another link. After reading both I couldn't find a passage talking about the actual authorization process.