How to make an M4B audiobook with chapters

An M4B is an audiobook in a single file. Under the hood it’s the same AAC audio as an M4A music file, with three things added: chapter marks, the book’s details (title, author, narrator), and the cover. The .m4b ending tells the player it’s an audiobook, so it remembers where you left off and files it with your audiobooks instead of your music.

M4B, or one file per chapter?

Depends where the book is headed.

Retailers and distributors like ACX and Spotify want one file per chapter, usually MP3, and build their own chapters out of those. Don’t send them an M4B.

If you’re selling or giving the book away yourself, from your own site, to Kickstarter backers, to a reviewer, M4B is the nicest thing you can hand someone. One download, and it opens in Apple Books and most audiobook players with the chapters and cover already in place.

It’s also an easy way to keep your own copy of each finished book.

What makes a good one

1. Chapters in the right spots. Each mark should sit just before the chapter starts, so skipping lands on the chapter heading and not mid-sentence. And the first chapter starts at the very beginning of the file.
2. Chapter names people can read. “Chapter 3: The Crossing” is a lot more useful in a chapter list than “Track 3.”
3. The details filled in. Title, author and narrator show up in the player and in their library.
4. A square cover. Audiobook covers are square, and a book-shaped cover gets cropped or boxed in. 2400 by 2400 pixels is what ACX asks for, and it looks good everywhere.
5. The same mastering as the rest of the book, so it sounds the same wherever somebody hears it.

Two kinds of chapter list

Here’s a fun one. There isn’t a single standard way to store chapters in an M4B. Apple’s players read a chapter track. A lot of Android and desktop players read a separate chapter list. A well-made M4B has both, so the chapters show up no matter what player somebody uses. If you’ve made an M4B before and the chapters only showed up in some players, that’s probably why.

Check it before you send it

Open it in at least two players, say Apple Books plus VLC or an Android audiobook app, and skip through every chapter. Make sure the cover and title show up. Then listen to the first and last few seconds of the file, and to the joins between chapters.