MP3 to M4B: one audiobook file with chapters
Drop the MP3s of a book, a course or a lecture series and get one .m4b file: each file becomes a chapter, with the title, the author and a cover. Audiobook apps show the chapters and remember where you stopped. Free, no signup, nothing is uploaded.
- One .m4b file, a chapter per MP3
- Title, author and cover included
- Audiobook apps remember where you stopped
- Free, no signup, nothing uploaded
One line per chapter: the time it starts, then its title. Leave empty for no chapters.
- Length
- -
- Chapters
- -
- File size
- -
- Time to make
- -
Nothing is uploaded. The audiobook is made in this tab; the only download is the converter itself (about 31 MB, once).
Which apps open an M4B with chapters
- Apple Books (iPhone, iPad, Mac). Shelves it under Audiobooks, with the cover, the chapter list and your place in the book. On a Mac, drag the file into Books; on an iPhone, save it to Files and share it to Books.
- BookPlayer (iPhone). Free player for your own audiobooks: chapters, speed, sleep timer.
- Smart AudioBook Player (Android). Reads the chapter list and keeps the position of each book.
- VLC (computer, Android, iPhone). Plays any M4B; the chapters are in the Playback menu.
- Audiobookshelf and Plex. Self-hosted libraries that read the chapters, the cover and the author.
How it works
- Add the files. Several files make one chapter each, in the order shown; drag the arrows to reorder, or sort by name. One long file can be cut into chapters with typed times.
- Check the chapters and the details. Chapter titles come from the file names without the track numbers; edit any of them. Add the title, the author and a cover.
- Make the M4B. The audio is encoded to AAC and packed with the chapter list in one file. An hour takes about half a minute on a computer.
M4B, M4A and MP3
An M4B is the same kind of file as an M4A (AAC audio in an MP4 container), with a chapter list and a flag that tells players "this is an audiobook". That is why Apple Books puts it on the audiobook shelf and players remember where you stopped, while a folder of MP3s plays like an album of songs. For speech, 64 kbps mono sounds the same as the original and makes about 30 MB an hour, so a ten-hour book fits in 300 MB.
Need one MP3 rather than an audiobook? Merge audio files joins recordings into one MP3. Have the book as text? Ebook to audiobook voices it chapter by chapter.
Questions
Not covered here? Ask us, we usually reply within a business day.
How do I convert MP3 to M4B?
Drop the MP3 files here, check the order and the chapter titles, add the title and a cover if you like, and press Make the M4B. You get one .m4b file with a chapter per MP3.
How do I add chapters to one long MP3?
Add the single file, then type one line per chapter under Chapter times: the start time and the title, like "4:35 Chapter 1". The first chapter always starts at 0:00.
Can I just rename an .m4a to .m4b?
It plays, but it has no chapters, no cover and no audiobook flag, so it is one long track. This page writes all three. If your files are already M4A, Keep the audio as is packs them without re-encoding, in seconds.
Which quality should I pick?
Speech (64 kbps mono) for audiobooks, lectures and courses: it sounds the same as the original voice and the file is half the size. Music and podcasts (128 kbps stereo) for recordings with music or stereo sound.
How long can the audiobook be?
Up to 12 hours in total on a computer and 3 hours on a phone, because the file is made in the browser's memory. Split a longer book into parts.
Can I upload the M4B to Audible?
No. Audible takes audiobooks only through ACX, with its own requirements. The M4B is for your own listening, your website, a course platform, or stores and libraries that accept M4B.
Are my files uploaded?
No. The audio is read, encoded and packed in this browser tab. The page downloads only the converter (ffmpeg for the web, about 31 MB, the first time).