Convert M4B to FLAC — Free Online Converter
Convert MPEG-4 Audiobook (.m4b) to Free Lossless Audio Codec (.flac) online for free. Fast, secure audio conversion with no watermarks or registration...
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変換方法
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.
About M4B to FLAC Conversion
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.
Why Convert M4B to FLAC?
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.
Common Use Cases
- Creating a lossless intermediate of audiobook audio before editing and remastering
- Archiving decoded audiobook content in an open-source lossless format
- Preparing audiobook audio for editing in Linux DAWs (Ardour, Audacity) that prefer FLAC
- Converting Apple audiobook purchases to a vendor-neutral archival format
- Providing lossless source files to audio editors who will reprocess the content
How It Works
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.
Quality & Performance
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 Compatibility
| Device | M4B | FLAC |
|---|---|---|
| Windows PC | Partial | Partial |
| macOS | Partial | Partial |
| iPhone/iPad | Partial | Partial |
| Android | Partial | Native |
| Linux | Partial | Native |
| Web Browser | No | No |
Recommended Settings by Platform
Spotify
Resolution: N/A
Bitrate: 320 kbps
OGG Vorbis preferred
Apple Music
Resolution: N/A
Bitrate: 256 kbps
AAC format required
SoundCloud
Resolution: N/A
Bitrate: 128 kbps
Lossless FLAC/WAV for best quality
Podcast
Resolution: N/A
Bitrate: 128 kbps
MP3 mono for spoken word
Tips for Best Results
- 1Export the M4B chapter list before conversion — use ffprobe to extract chapter timestamps
- 2FLAC compression level 5 is optimal — higher levels save minimal additional space for audiobook content
- 3Mono output is fine for single-narrator audiobooks — no need for stereo FLAC
- 4Use this conversion as a processing intermediate, not as a final listening format
Related Conversions
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.