FormatDrop doesn't convert AAX to M4B yet. The methods below use free tools that do. FormatDrop's own converters cover common image, audio, video and PDF formats, all in your browser.
Your options for Audible AAX files
- 1
Keep listening in Audible
Audible's apps (iPhone, iPad, Android, Mac, Windows) and audible.com in a browser already give you chapters, bookmarks and synced progress for AAX books.
- 2
For Plex or Apple Books, you need DRM-free files
Plex and Apple Books can't play Audible's AAX files. Libro.fm sells DRM-free audiobooks as M4B or MP3 downloads, and LibriVox has free public-domain M4B audiobooks; both drop straight into Plex or Apple Books.
- 3
Join DRM-free MP3s into one M4B
If a DRM-free book came as many MP3 files, m4b-tool merges them into one M4B with chapters: m4b-tool merge mp3-folder/ --output-file=book.m4b. It needs FFmpeg.
Why convert AAX to M4B?
M4B is the audiobook format with proper chapter support. Converting AAX to M4B preserves the audiobook structure that AAX already has, just in a more open container.
Frequently asked questions
Is AAX to M4B lossless?
AAX does hold AAC audio in an MPEG-4 container, like M4B, but the audio is encrypted. Without breaking the DRM there's nothing to remux. DRM-free M4B files need no conversion at all.
Why M4B instead of MP3 for audiobooks?
M4B is purpose-built for audiobooks: chapter navigation, bookmarking, and resume playback are first-class features. MP3 with chapter tags works but lacks the polished UX of dedicated audiobook formats. Apple Books, Plex, and most modern audiobook apps treat M4B differently from MP3.
Can I split chapters into separate M4B files?
For DRM-free M4B files, yes: `m4b-tool split --audio-format m4b book.m4b` writes one file per chapter. Audible's own apps let you jump between chapters without splitting.
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