Convert MPEG-4 Audiobook (.m4b) to Free Lossless Audio Codec (.flac) online for free. Fast, secure audio conversion with no watermarks or registration.
Upload your .m4b file by dragging it into the upload area or clicking to browse.
Choose your output settings. The default settings work great for most files.
Click Convert and download your .flac file when it's ready.
Converting M4B audiobooks to FLAC decodes the compressed AAC speech audio and stores it in the Free Lossless Audio Codec. Since M4B uses lossy AAC at low bitrates (32-64 kbps for spoken word), the FLAC output preserves the decoded signal losslessly but does not recover quality lost during the original AAC encoding. The resulting FLAC file is substantially larger than the M4B with no audible improvement. Chapter markers and bookmarking are not preserved.
Archival-minded users may want a lossless copy of the decoded audiobook to prevent further generational loss during future re-encoding. Audio producers editing audiobook content prefer working with lossless formats to avoid cascading lossy-to-lossy degradation when processing and re-exporting. FLAC also serves as a vendor-neutral archival format compared to Apple's M4B.
FFmpeg decodes the M4B's AAC audio to PCM and encodes with the FLAC reference encoder. For 10-hour audiobook at 64 kbps M4B (~28 MB), the FLAC output is approximately 270 MB (mono, 16-bit, 44.1 kHz). FLAC compression level 5 (default) provides a good speed/size balance. Vorbis comment metadata can store title, narrator, and other audiobook info, but chapter data from M4B is not preserved in FLAC.
Identical to M4B playback quality. No improvement. The FLAC losslessly stores the decoded AAC signal with all its compression artifacts. The file grows approximately 10x with no change in what you hear.
| Device | M4B | FLAC |
|---|---|---|
| Windows PC | Partial | Partial |
| macOS | Partial | Partial |
| iPhone/iPad | Partial | Partial |
| Android | Partial | Native |
| Linux | Partial | Native |
| Web Browser | No |
Resolution: N/A
Bitrate: 320 kbps
OGG Vorbis preferred
Resolution: N/A
Bitrate: 256 kbps
AAC format required
Resolution: N/A
Bitrate: 128 kbps
Lossless FLAC/WAV for best quality
Resolution: N/A
Bitrate: 128 kbps
MP3 mono for spoken word
M4B to FLAC is an archival and production workflow conversion. Use it when you need a lossless intermediate or an open-source format for your audiobook audio. Quality matches the M4B original exactly.
Безопасная передача
Загрузки зашифрованы по HTTPS
Конфиденциальность прежде всего
Файлы автоматически удаляются после обработки
Без регистрации
Начните конвертировать мгновенно
Работает везде
Любой браузер, любое устройство
| No |
| Характеристика | M4B | FLAC |
|---|---|---|
| Полное название | MPEG-4 Audiobook | Free Lossless Audio Codec |
| Расширение | .m4b | .flac |
| Лучше всего подходит для | Chapter support | Lossless compression |