mp3tom4b

Convert MP3 to M4B audiobooks without uploading a single byte.

Drag your files in, add a cover and chapters, get a single tagged M4B out.

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 *

Author *

Narrator (optional)

Year (optional)

Genre

Verify metadata (optional)

Enter a title, author, or narrator first.

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

64 kbps· recommended for audiobooks (spoken word)

To 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