Audio
What is a M4B file?
M4B is an MPEG-4 audio format built specifically for audiobooks and podcasts. It's based on the same AAC compression used in M4A files, but adds chapter markers and remembers your playback position across an entire book. The tradeoff is that it's lossy, built for compressed speech rather than archiving high-fidelity audio.
- Extension
- .m4b
- Type
- Audio
- Typically
- Audiobooks, podcasts
- Compression
- Lossy
Why M4B exists
M4B grew out of Apple's M4A audio format, adapted to hold long spoken-word recordings. The built-in audiobook app on Apple devices, and the media library app that came before it, treats M4B as the standard container for audiobooks, which is why the extension shows up so often on Mac and iPhone.
Where a single MP3 usually covers one track, an M4B can hold an entire multi-hour audiobook as one file, split internally into chapters you can jump between. It also saves your last playback position inside the file itself, so picking up where you left off doesn't depend on the app remembering separately.
Podcasters and audiobook producers export in M4B specifically to preserve that chapter structure. But plenty of players and car stereos only recognize MP3, so people end up converting M4B down to MP3 for compatibility, or combining a folder of MP3 chapters into a single M4B for a cleaner audiobook file.
The trade-offs
Strengths
- Bundles an entire audiobook or podcast into one file instead of dozens of tracks
- Chapter markers let you skip between sections instead of scrubbing
- Remembers your playback position automatically
- Smaller files than uncompressed audio at similar quality
Watch-outs
- Lossy: some audio detail is discarded during compression
- Not read by every media player, especially older or generic MP3 players
- Chapter and bookmark support varies between apps
- Harder to edit or split than plain MP3 files
A note on privacy
An M4B file can carry embedded metadata like title, author, and cover art. Running it through an online converter means uploading the whole audiobook or podcast to someone else's server just to change its format. Converting on your own machine keeps the file, and that metadata, on your computer the whole time.
Convert a M4B file
- Convert M4B to MP3
- Convert M4B to WAV
- Convert M4B to FLAC
- Convert M4B to AAC
- Convert M4B to M4A
- Convert M4B to OGG
Questions
How do I open an M4B file?
The built-in audiobook and music apps open M4B natively on Mac and iPhone. On Windows or Android you'll usually need a media player that supports M4B, or you can convert it to MP3 first.
Is M4B better than MP3?
M4B keeps chapter markers and bundles a whole audiobook into one file, which MP3 doesn't handle well. MP3 wins on compatibility since almost every device and player reads it without issue.
Why does my audiobook app save files as M4B?
Audiobook apps use M4B because it supports chapters and stores your playback position inside the file, which matters for something you might listen to over several sittings.
Can I convert M4B without uploading it?
Yes. A desktop app like Morphjet converts M4B on your own computer, so the audiobook never has to leave your machine.
Morphjet opens and converts M4B, one of 2,748 conversions it runs on your own computer. Available now.
One-time purchase, no subscription. 14 days to change your mind.