M4A to M4B
Turn M4A audio files into a proper chaptered M4B audiobook — the format Apple Books, Plex, and other players recognise as a book rather than music. Your files never leave your device.
Drop audio files + cover image, or click to browse
MP3 · M4A · WAV · FLAC · OGG · Opus · JPG · PNG
New here? M4B is the audiobook format Apple Books, Plex, and most modern players recognise — chapters, cover art, and resume position in one tagged file. Drop your audio in and you'll get back a single M4B with chapters at every file boundary.
- One chapter per file, titled from the filename
- Optional cover art, embedded at 1200×1200
- More detail on the FAQ page
Audiobook details
Title is required.
Author is required.
Verify metadata (optional)
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 kbps, 192 kbps, 256 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.
M4A to M4B — common questions
- What is the difference between M4A and M4B?
- M4A and M4B use the same AAC audio codec inside an MP4 container — the only difference is the file extension and how players treat them. Players like Apple Books and Plex recognise M4B as an audiobook, which means they remember your playback position and display chapter navigation. M4A files are treated as music and lose those features.
- Can I just rename M4A to M4B instead of converting?
- Sometimes — if you have a single M4A file with no chapter markers you want to preserve, renaming works. But mp3tom4b does much more: it joins multiple M4A files into one, adds chapter markers at every file boundary, embeds cover art, and writes title/author/narrator metadata into the container. A simple rename cannot do any of that.
- I have M4A files from iTunes purchases. Will this work?
- If the files are DRM-free (most purchases since 2009 are), yes — they will convert normally. DRM-protected M4A files (FairPlay) cannot be processed by any client-side tool, including this one. Check whether your files play in a non-Apple player to tell them apart.
- Are my M4A files uploaded anywhere?
- No. Conversion runs entirely inside your browser using a WebAssembly build of FFmpeg. Your files never touch any server. Open the Network tab in your browser's developer tools while converting to confirm there are no upload requests.