mp3tom4b
Convert MP3 to M4B audiobooks right in your browser. Drag your files in, add a cover and chapters, get a single tagged M4B out — nothing is uploaded.
Drag audio files here, or click to browse
MP3 · M4A · WAV · FLAC · OGG · Opus
Audiobook details
Title is required.
Author is required.
Cover image (optional)
Drop or click to add cover
JPG · PNG
Square images work best. Non-square covers are padded to 1200×1200 with a white background and embedded as JPEG.
Output bitrate
96 kbps, 128 kbpsTo enable: add at least one audio file, enter a title, enter an author.
How it works
- Step 1
Drop your files
Drag MP3, M4A, WAV, FLAC, OGG, or Opus files into the browser. They stay on your device.
- Step 2
Add metadata
Reorder chapters, set the title, author, narrator and cover. Embedded tags auto-fill what they can.
- Step 3
Download M4B
A single tagged, chaptered audiobook — ready for Apple Books, Plex, or any M4B-aware player.
Why mp3tom4b?
Every other browser-based MP3-to-M4B converter we've found uploads your audio to a server for processing. We don't — the conversion runs entirely in your browser via WebAssembly.
| mp3tom4b | Typical web converters | |
|---|---|---|
| Files leave your device | Never | Uploaded to a server |
| Account / signup | None | Often required |
| Free tier limits | No artificial caps | "Free" then paywalled |
| Source code | Open on GitHub | Closed |
| Works offline | After first load | Server-dependent |