M4B to MP3 Converter
Convert M4B audiobook files (Apple's audiobook format) into universally-playable MP3. Ideal for iTunes audiobooks, Apple Books exports, and non-DRM Audible content that needs to play outside the Apple ecosystem.
Drop your M4B file here or click to browse
M4B (.m4b) · Max 20 MB
Free — 10-second preview, 5 conversions/month. Upgrade for unlimited
What is M4B?
Apple Audiobook format — MPEG-4 container with AAC audio and chapter metadata. Used by iTunes audiobooks, Audible (non-DRM), and Apple Books. Bookmark-aware playback distinguishes it from M4A.
What is MP3?
The most widely used audio format. Great compatibility, small file size. Ideal for music, podcasts, and general use.
Why Convert M4B to MP3?
M4B is Apple's audiobook format — an MPEG-4 container wrapping AAC audio with embedded chapter metadata for bookmark-aware playback. It's nearly identical to M4A but the .m4b extension tells iOS and macOS to treat the file as an audiobook (resume position, chapter navigation, faster playback in audiobook apps). The problem: outside the Apple ecosystem M4B is poorly supported. Most car stereos, MP3 players, podcast apps, and Android tools won't recognize it as audio — even though it contains the same AAC codec as everything else. Converting M4B to MP3 keeps the audio playable on every device made in the last 20 years. The conversion strips the chapter metadata (which becomes a feature in audiobook-aware players but is just lost data elsewhere) and re-encodes the AAC audio to MP3 at your chosen bitrate. For long audiobook listening, 64-96 kbps mono MP3 is plenty for spoken content and produces files small enough to fit hundreds of hours on a phone. AudioUtils runs the entire conversion in your browser — your audiobook never leaves your device, which matters because purchased audiobook content lives in a legal-but-private zone you don't want logged on someone else's server.
Who Uses This Converter
Audiobook for car listening
Convert M4B audiobooks to MP3 for playback on USB-equipped car stereos that don't support Apple's audiobook format.
Migration off Apple Books
Moving audiobook library to Android, Linux, or non-Apple devices? Convert M4B to MP3 for cross-platform compatibility.
LibriVox public-domain books
LibriVox offers free public-domain audiobooks in M4B. Convert to MP3 if your player doesn't support M4B natively.
Long-form podcast distribution
Re-purposing an audiobook chapter as a podcast episode? MP3 is the universally-accepted podcast distribution format.
Frequently Asked Questions
Will this work on DRM-protected Audible (.aax) files?
No. AAX files from Audible are DRM-protected and require Audible authentication to decode — that's not possible in a browser-based privacy-first tool. This converter handles M4B files that are already non-DRM: your own iTunes audiobooks ripped from CD, Apple Books exports, DRM-free Audible promotional content, or M4B files from open-source audiobook services like LibriVox.
Will the chapter metadata be preserved?
No. MP3 doesn't support the same chapter format as M4B. The conversion produces a single continuous MP3 file. If chapter-aware playback matters, keep the M4B and use an audiobook player like Audiobook Shelf or Smart Audiobook Player (which support M4B natively on most platforms). If you need split files per chapter, use a desktop tool like ffmpeg with chapter-split options after the M4B → MP3 conversion.
What bitrate should I choose for an audiobook?
For spoken-word content (most audiobooks), 64-96 kbps mono is plenty. Voice has low information density compared to music. A 10-hour audiobook at 96 kbps mono is about 432 MB total — fits comfortably on any phone. At 128 kbps you're using more space without audible improvement for voice. Reserve 192+ kbps for audiobooks with music or sound effects.
Why are M4B and M4A different if they have the same codec?
The .m4b extension is a hint to iOS, macOS, and audiobook apps that the file should be treated as an audiobook — resume-position memory, chapter navigation, speed control optimized for speech. The internal audio data is identical to M4A (AAC in MPEG-4). Renaming an .m4b to .m4a removes the audiobook flag but keeps the audio playable in regular music apps.
Will this work on LibriVox audiobooks?
Yes. LibriVox provides public-domain audiobooks in M4B format (alongside MP3 and ZIP downloads of individual chapter files). The M4B versions convert cleanly with this tool, useful when you want a single combined MP3 file from the LibriVox M4B.
How big can the M4B file be?
Free tier handles files up to 20 MB; Pro handles up to 500 MB. Audiobook M4B files can range from 50 MB (short books) to 1+ GB (epic fantasy, 30+ hours). For large audiobooks beyond Pro's limit, split the M4B into chapter chunks with a desktop tool first, then convert each chunk.
Will the converted MP3 play in my car?
Yes. The output is a standard MP3 that plays on every car stereo with USB/Bluetooth, every smartphone, every Bluetooth speaker, and every device made in the last 20 years. That's the main reason to convert from M4B in the first place — universal compatibility.