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.
How to convert WAV chapter files to M4B
- Export one WAV per chapter with zero-padded names. WAV carries no tag Kataribe reads, so the filename decides both order and default chapter title. Chapter_01.wav through Chapter_24.wav sort correctly; "Intro.wav" and "Credits.wav" won't, so give them 00 and 99 prefixes or move them with the row arrows after dropping.
- Rename the chapters to what the listener should see. The default title is the filename with underscores turned to spaces and the extension removed. Type the real chapter name over it; the text goes into the chapter marker exactly as typed, including numbering if you want it.
- Choose the bitrate from the master's channel format. For mono narration, 64 kbps AAC is the retail norm and is transparent from a lossless source. For a stereo master, or one with music cues, choose 96 or 128; the encoder keeps stereo, and 64 kbps shared across two channels is thin.
- Add the cover and the credits fields. Drop a square JPEG or PNG; it is embedded at its original resolution, so a 1400 to 2400 pixel export is plenty and a print-resolution file only bloats the book. Fill in title, author (you) and narrator (the voice), plus the year; genre is preset to Audiobook.
- Build on a desktop browser and wait for the download. Every WAV is decoded and encoded in sequence, so a 24-file book runs for several minutes and the progress bar advances per file. The download appears when the final mux finishes; keep the tab open until then.
Choosing a bitrate for narration
The five options are 32, 48, 64, 96 and 128 kbps, and for speech the differences are smaller than for music. Per hour of audio that is roughly 14, 22, 29, 43 and 58 MB. A single voice in mono at 64 kbps is what most stores deliver; 48 is acceptable for a plain reading and 32 is audibly rough on sibilants.
Coming from a WAV master you get the best case for the encoder: no earlier lossy pass, full bandwidth, and a stable noise floor if the studio did its job. That is the argument for not going above 64 for mono speech; the extra bits at 128 mostly encode room tone.
Mono or stereo: decide before you drop
Kataribe doesn't add a channel-mixing step. A stereo export of a single narrator doubles the data the encoder must fit into the same bitrate and gains nothing, since both channels carry the same voice. Bounce mono from the session for narration and reserve stereo for productions with music beds or multiple positioned voices.
Mixing channel formats inside one book is legal but unwise: each file is encoded with its own layout and the parts are joined as they are, so a stereo intro followed by mono chapters produces a layout change at the join. Some players handle it, some hiccup. Keep every file in a book the same format.
Where the credits end up in the file
Author is written to the artist and album artist atoms, narrator to composer, year to the date atom, and the title to both title and album. Audiobookshelf reads composer as the narrator field; Apple Books shows title, author and cover. There is no separate series or subtitle field, so include a subtitle in the title if you need it.
The download is named Author - Title.m4b from those two fields, with characters filesystems reject removed. Rename it freely; players read the tags, not the filename, and the retailer deliverables (usually per-chapter MP3 at a fixed spec) should be produced from the WAVs separately.
After you download the .m4b
Apple Books
- Mac: drag the .m4b into Books, or File → Add to Library. It lands under Audiobooks with the cover and chapters.
- iPhone / iPad: connect the device and sync audiobooks in Finder (or iTunes on Windows), or AirDrop the file and open it in Books.
- 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
- Copy the .m4b into your library folder as Author/Title/Book.m4b (or upload it from the web UI).
- Run a library scan; Audiobookshelf reads the embedded title, author, narrator, cover, and chapter markers.
- Chapters appear in the player on web, iOS, and Android — no chapter files or metadata edits needed.
Android players
- Copy the .m4b to the phone (USB, Drive, or Syncthing) into a folder your player watches.
- Smart AudioBook Player, Listen, Voice, and the Audiobookshelf app all read M4B chapters and cover art.
- 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.
- Can I drop one WAV of the whole book?
- Yes, and it will build, but the result has one chapter. Kataribe never splits a file; chapters come only from file boundaries, so export per-chapter WAVs from the session if you want a chapter list.
- Does Kataribe downmix stereo to mono?
- No. Channel count is passed through: a stereo WAV becomes stereo AAC and a mono WAV becomes mono AAC, at the bitrate you picked for the whole file. Decide the channel format in the export from your DAW.
- Should I normalize or compress the WAVs first?
- Yes, before dropping them. Kataribe applies no loudness processing, noise reduction or trimming, so whatever level and room tone the WAVs have is what the book has. Get the masters where you want them, then encode.
- 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.