Convert MP3 to M4B for Audiobookshelf

Audiobookshelf reads a chaptered .m4b the way you'd hope: one file, chapters from the embedded markers, cover and metadata from the tags. Kataribe builds that file from a folder of MP3s in your browser, before anything touches the server.

Moving a collection into Audiobookshelf is when the folders show their age. A book of 60 MP3s works, but it's 60 files to copy, chapter names that are whatever the tags said, and a cover that may or may not be picked up. Drop the 60 files here, check the pre-filled title, author and narrator, tidy the chapter names, and put one .m4b in the library folder. On scan, Audiobookshelf reads the chapters, cover and metadata straight from the file, with nothing to match by hand.

Because the encode happens on your laptop rather than the server, it doesn't matter if Audiobookshelf runs on a Raspberry Pi or a low-power NAS. One book per build; for a whole shelf, work through them one at a time, and for very large sets (10 GB or more of input) build in parts.

After you download the .m4b

Audiobookshelf

  1. Copy the .m4b into your library folder as Author/Title/Book.m4b (or upload it from the web UI).
  2. Run a library scan; Audiobookshelf reads the embedded title, author, narrator, cover, and chapter markers.
  3. Chapters appear in the player on web, iOS, and Android — no chapter files or metadata edits needed.

Frequently asked questions

Audiobookshelf can make an M4B itself. Why do it here?
It can, using the server's CPU, and on small hardware a long book is slow and ties the server up. Kataribe does it in your browser before upload, with chapter titles and metadata fixed first, so the file lands in the library finished.
Will Audiobookshelf pick up the chapters automatically?
Yes. Chapter markers embedded in the M4B are read on scan and appear in the chapter panel. The embedded cover is used, and title, author and narrator tags are read subject to the metadata priority set for the library.
Should I keep the MP3s as well?
Your choice; the M4B is a re-encode, so keeping the originals costs only disk. Don't put both in the same book folder, or the scan treats them as one book with duplicate tracks.
Does the file name matter?
Audiobookshelf reads author and title from the folder path first (Author/Title/book.m4b), so name the folders the way you already do. The .m4b itself can be called anything.
Are my audio files uploaded anywhere?
No. Kataribe runs FFmpeg compiled to WebAssembly inside your browser, so the files never leave your device. The engine (about 30 MB) downloads once and is cached; after that there is no account, no queue and no watermark.
How long does a full book take?
Encoding runs many times faster than real time on a modern laptop, but a full-length book still takes minutes, not seconds. Keep the tab open until the download appears. If every input is already AAC, the audio is copied rather than re-encoded, which is much quicker.
Is this really free?
Yes. Every input format, every bitrate, cover art and metadata, no sign-up, and nothing added to the audio.
Does it work with DRM-protected audiobooks?
No. DRM-protected files (Audible .aax and similar) won't open, and we don't help with that. Kataribe is for audio you already have in plain MP3, M4A, WAV, FLAC or OGG.