"While books that come on audio CDs don't have DRM embedded in them, files downloaded from Audible or other for-pay sources often do. Audiobookshelf won't play books with DRM, which means you need a method of stripping that DRM out.
Unfortunately, here's where we run into a problem: removing DRM from your audiobooks is not universally legal. "In the US, the law against 'circumventing' effective DRM has no personal-use exemption. In Europe, it varies by country," explained the Electronic Frontier Foundation's Competition and IP Litigation Director Mitch Stoltz when Ars reached out for advice. "That's as silly as it sounds—stripping DRM from one’s own copy of an audiobook in order to listen to it privately through different software doesn’t threaten the author or publisher, except that it makes it harder for them to charge you twice for the same audiobook. It’s another example of how anti-circumvention laws interfere with consumers’ rights of ownership over the things they buy."
And that means you're kind of on your own for this step. Should you live in a jurisdiction where DRM removal from audiobooks for personal use is legal—which includes some but not all European countries—then sites like this one can assist in the process; for the rest of us, the only advice I can give is to simply proceed in a legal manner and use DRM-free audiobooks to start with."
https://arstechnica.com/gadgets/2025/03/i-threw-away-audibles-app-and-now-i-self-host-my-audiobooks/