How to convert an audiobook M4B to MP3 on a Mac

23 August 2026 · 6 min read

An M4B file is an ordinary AAC audio file in an MP4 container, with an extension that tells Apple’s apps to treat it as a book (remember your place, show chapters) rather than a song. If the book is not copy-protected, converting it to MP3 works like any other audio conversion: the Music app can do it after a rename, and Manatee does it by drag and drop. If the book was bought with copy protection, no converter on a Mac will open it, and the honest advice is to play it in the app it came from.

First, find out whether the book is protected

This determines everything, so check before you spend time on it.

Select the file in Finder and press Command-I for Get Info.
Look at the Kind line. “MPEG-4 audio” or “Audiobook” means a plain file and you can proceed. “Protected MPEG-4 audio” means it carries digital rights management (DRM).
Files with .aa or .aax extensions from subscription audiobook stores are always protected, regardless of what Finder says.

Protected files are encrypted to a specific account. Manatee does not remove copy protection and does not crack passwords; it will report the file as something it cannot convert. Books you ripped from your own CDs, bought from DRM-free stores, downloaded from public-domain libraries, or recorded yourself are the ones this guide is for.

What you lose by going to MP3

Before converting, it is worth asking whether you need to. M4B is supported by the Books app, every iPhone and iPad, most Android players, and nearly every dedicated audiobook app. MP3 is only necessary for old car stereos, inexpensive MP3 players, and some software that refuses anything else. If that is your situation, here is what the conversion costs.

Chapters. M4B carries chapter markers, so you can skip to “Chapter 12” in a player. MP3 has no widely supported equivalent. A converted book becomes one long track.
Resume position. Players remember where you stopped in an audiobook file; many treat an MP3 as music and start from the beginning each time.
A second round of compression. The M4B is already lossy (AAC). Encoding it to MP3 discards a bit more. Spoken word is forgiving, and at 96 kbps or above the difference is hard to notice, but it is there.
Practicality. A ten-hour book becomes a single MP3 of several hundred megabytes. Some players handle that gracefully; some choke.

If the source came as one M4B per chapter, converting each file keeps the chapter structure as separate MP3s, which is the best outcome available.

Convert with Manatee

Manatee accepts .m4b as an input type and writes MP3 as a target. It converts the whole file to a single MP3; it does not split on chapter markers, and it is not an audio editor.

Open Manatee. It is free with every feature for 24 hours, no account or card, then $9 once.
Drag the M4B, or a folder of chapter files, onto the menu bar icon or into the window’s drop zone.
Choose Convert and pick MP3.
Each job writes an MP3 beside the original. The original is never modified, so if you decide later that you preferred the M4B, it is still there.

Because everything runs on the Mac, a long book converts at whatever speed your processor allows, and nothing is uploaded. If Manatee reports that it cannot open the file, go back to the first section: the file is almost certainly protected.

Convert with the Music app

The Music app contains an MP3 encoder, but it has a quirk with audiobooks: on recent versions of macOS, double-clicking an M4B opens the Books app, not Music, and Books has no converter. The workaround is a rename.

Duplicate the M4B in Finder (Command-D) so you keep an untouched copy.
Rename the duplicate’s extension from .m4b to .m4a. The contents are identical; only the label changes. Confirm when Finder asks.
Open Music. Choose Music, Settings, then Files, then Import Settings. Set Import Using to MP3 Encoder, pick a quality (Good Quality at 128 kbps is fine for speech), and click OK twice.
Drag the renamed .m4a into the Music window to add it to the library.
Select the track and choose File, Convert, Create MP3 Version.
When the new track appears, right-click it and choose Show in Finder to get the MP3.
Set Import Settings back to what it was, so future imports are not converted to MP3 by accident.

Music also converts the whole file to one track. If the book has chapter markers they are dropped, exactly as with any other converter.

Keeping chapters, if you need them

There is no conversion setting that turns one M4B into per-chapter MP3s. Your options are:

Get per-chapter files from the source. Many DRM-free stores and library services offer a ZIP of chapter files alongside the single M4B.
Keep the M4B. If the player you are targeting supports it, this is the better file in every way.
Split the MP3 afterward in an audio editor, using the chapter times from the Books app as a guide. This is tedious for a long book, which is why the first two options come first.

For a related conversion that does not involve audiobooks, how to convert M4A to MP3 on a Mac covers ordinary AAC files, and lossless vs lossy explains why the second round of compression is worth avoiding when you can.

Questions

Is M4B just M4A with a different extension?

Technically, yes, with two additions: the file is flagged as an audiobook so players remember your position, and it usually carries chapter markers. Renaming .m4b to .m4a works because the container is the same.

Why does my converter say it cannot open the file?

Almost always because the file is copy-protected. Check Get Info for “Protected” in the Kind line. No legitimate converter on a Mac will open a protected audiobook, and Manatee is no exception.

Will the MP3 sound worse?

Slightly, in principle, since AAC to MP3 is a lossy-to-lossy conversion. For narrated speech at 96 kbps or higher it is very hard to hear. Avoid going lower than 64 kbps.

Can I convert the other way, MP3 to M4B?

Manatee writes M4A, not M4B, but since the container is the same you can convert to M4A and rename the result to .m4b. You will get a file the Books app treats as an audiobook, without chapter markers.