Add chapters to an M4B audiobook

Chapters in an M4B are markers inside the file, and Kataribe writes them: one per input file. Drop the parts of a book — MP3, M4A, WAV, FLAC, OGG, or M4A/M4B parts — and get one .m4b whose chapter list matches the files, built in your browser.

A language course is a good example: 30 lesson files, each an M4A named lesson01 to lesson30. Dropped here, they become one book with 30 chapters, ordered naturally (lesson10 after lesson09), titled from the tags or filenames, and renamable to "Lesson 3: At the market" before building. Because the audio is already AAC, it's copied rather than re-encoded, so the build is quick and nothing is lost. Jumping between lessons in Apple Books or Audiobookshelf then works from the chapter list instead of scrubbing.

Two limits worth knowing. Chapters aren't detected from silence, so a single long file becomes a single chapter — to get real chapters, start from the per-chapter files. And an existing M4B isn't edited in place: dropping one rebuilds it with the title, cover and metadata you set, which is the way to fix a book with the wrong author or no cover, but the chapter structure still follows the files you drop.

After you download the .m4b

Apple Books

  1. Mac: drag the .m4b into Books, or File → Add to Library. It lands under Audiobooks with the cover and chapters.
  2. iPhone / iPad: connect the device and sync audiobooks in Finder (or iTunes on Windows), or AirDrop the file and open it in Books.
  3. Books remembers your position and shows the chapter list from the file — that's the whole point of M4B over a folder of MP3s.

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.

Android players

  1. Copy the .m4b to the phone (USB, Drive, or Syncthing) into a folder your player watches.
  2. Smart AudioBook Player, Listen, Voice, and the Audiobookshelf app all read M4B chapters and cover art.
  3. One file per book means one entry in the library, with your position remembered across chapters.

Frequently asked questions

I have one long M4B with no chapters. Can Kataribe split it up?
Not on its own. Chapters are one per input file and there's no silence detection. If you still have the files the M4B was built from, drop those instead. Splitting an M4B into pieces is a different tool.
My M4B has the wrong title and no cover. Can I fix that?
Yes. Drop the M4B, change the title, author, narrator and year, drop in a cover, and build; the AAC audio is copied, not re-encoded. Chapters follow the files you drop, so if the original had chapters you want kept, rebuild from the per-chapter source files.
Can I rename the chapters?
Yes. Every chapter title is editable before you build. Defaults come from the ID3 title tag or a cleaned-up filename, so lesson07.m4a starts as "lesson07" and can be whatever you type.
Does re-chaptering M4A parts re-encode the audio?
No. When every input is AAC (M4A or M4B), the audio is copied into the new container and only chapter markers, cover and metadata are written. Mixed inputs are encoded at the bitrate you pick.
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.