Convert WAV to M4B

Studios deliver narration as WAV: one file per chapter, hundreds of megabytes each. Kataribe encodes them to AAC and packs them into a single .m4b with chapters, cover and metadata, in your browser, without uploading a byte.

For an author with a finished narration, this is the step between the master files and something a reader can listen to. Drop Chapter_01.wav through Chapter_24.wav at once — natural filename order keeps 10 after 9 — set the title, your name as author and the narrator's name, drop in the cover, and build. Chapter titles start as cleaned-up filenames and every one can be typed over, so "Chapter_03" becomes "3. The Long Road" before the book is made.

WAV carries no tags, so expect to fill the book details in yourself; it's four fields and a cover. 64 kbps AAC is what many commercial audiobooks ship at; 96 or 128 keeps more headroom if the production has music. Files are encoded one at a time, so a full book fits in a desktop browser. This isn't a mastering step: levels, noise and pacing should be fixed in the WAVs first.

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

Why make an M4B instead of sending the WAVs?
Size and structure. A 10-hour book in 16-bit 44.1 kHz WAV is around 3 GB in mono and twice that in stereo; the same book at 64 kbps AAC is under 300 MB, plays as one file with chapters, and opens in any audiobook app.
Can I set the narrator separately from the author?
Yes. Title, author, narrator and year are separate fields, and the genre is written as Audiobook. Apple Books and Audiobookshelf show author and narrator as distinct people.
Is the M4B what I send to retailers?
Send it to readers, reviewers and your own library, yes. Retail platforms have their own upload specs, usually per-chapter MP3 at set levels, so check theirs and keep the WAVs as your masters.
My WAVs are 24-bit or 96 kHz. Will they work?
Yes. Any WAV FFmpeg can read is accepted, and the audio is encoded to AAC at the bitrate you choose. Mono or stereo is preserved from the source.
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.