What is a .m4b file?
MPEG-4 Audiobook · Audio · Apple / MPEG · 2003
An .m4b file is an MPEG-4 audiobook, the same container as M4A but with chapter markers and the ability to remember your place. It is the standard audiobook format in Apple's ecosystem.
What is a .m4b file used for?
M4B is an ISO base-media file (ftyp box at offset 4) holding AAC audio plus chapter and bookmark data. The extension tells apps to treat it as a resumable audiobook rather than a song.
Apple Books and many audiobook players read it. Some M4B files from stores carry DRM; DRM-free ones convert to MP3, though you lose chapters.
How to open a .m4b file
The .m4b format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .m4b file.
Windows
- VLC
- AIMP
- Audiobookshelf
macOS
- Apple Books
- VLC
- Audiobookshelf
Linux
- VLC
- Cozy
- ffmpeg
How to convert a .m4b file
You can convert a .m4b file to mp3, m4a, aac using a conversion tool or the export menu of an app that opens it.
.m4b file signature (magic bytes)
Programs recognise a .m4b file by the bytes at the start of the file, not by its name. These are the signatures for M4B. For a full breakdown, see the M4B file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 66 74 79 70 | 4 | ftyp box (ISO base media) |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .m4b file?
An .m4b file is an MPEG-4 audiobook, the same container as M4A but with chapter markers and the ability to remember your place. It is the standard audiobook format in Apple's ecosystem.
How do I open an .m4b file?
Apple Books plays it on Apple devices; VLC and audiobook apps like Audiobookshelf open it elsewhere, keeping the chapters.
What is the difference between M4A and M4B?
Both are MPEG-4 audio. M4B adds chapters and remembers your position, and apps treat it as an audiobook rather than music.
Why won't my .m4b file play?
It may carry DRM from an audiobook store, which locks it to that store's app. DRM-free M4B files play in VLC and most audiobook players.
Related formats
Sources
Details on this page were checked against authoritative references: