FLAC to M4B
Convert lossless FLAC audio into a chaptered M4B audiobook — right in your browser. Chapter markers, cover art, and embedded metadata are all included. Your files never leave your device.
Drop audio files + cover image, or click to browse
MP3 · M4A · WAV · FLAC · OGG · Opus · JPG · PNG
New here? M4B is the audiobook format Apple Books, Plex, and most modern players recognise — chapters, cover art, and resume position in one tagged file. Drop your audio in and you'll get back a single M4B with chapters at every file boundary.
- One chapter per file, titled from the filename
- Optional cover art, embedded at 1200×1200
- More detail on the FAQ page
Audiobook details
Title is required.
Author is required.
Verify metadata (optional)
Cover image (optional)
Drop or click to add cover
JPG · PNG
Square images work best. Non-square covers are padded to 1200×1200 with a white background and embedded as JPEG.
Output bitrate
96 kbps, 128 kbps, 192 kbps, 256 kbpsTo enable: add at least one audio file, enter a title, enter an author.
How it works
- Step 1
Drop your files
Drag MP3, M4A, WAV, FLAC, OGG, or Opus files into the browser. They stay on your device.
- Step 2
Add metadata
Reorder chapters, set the title, author, narrator and cover. Embedded tags auto-fill what they can.
- Step 3
Download M4B
A single tagged, chaptered audiobook — ready for Apple Books, Plex, or any M4B-aware player.
FLAC to M4B — common questions
- Does converting FLAC to M4B lose quality?
- Yes — FLAC is lossless and M4B uses AAC, which is lossy. For spoken-word audiobooks the difference is inaudible at 64 kbps; that is the default and the standard for audiobook distribution. If you have music or high-fidelity content, choose 128 kbps in the bitrate selector.
- Can I mix FLAC and MP3 files in the same audiobook?
- Yes. mp3tom4b re-encodes every input file to AAC before joining them, so mixed formats work fine. Drop FLAC and MP3 files together and they will be combined into one M4B in the order you arrange them.
- Why are my FLAC files large but the M4B is small?
- FLAC files store audio losslessly, which is much larger than AAC. A 500 MB FLAC audiobook will typically produce an M4B of 100–150 MB at 64 kbps — perfectly normal and the right trade-off for spoken audio.
- Are my FLAC files uploaded for conversion?
- No. The entire conversion runs in your browser via a WebAssembly build of FFmpeg. Nothing leaves your device. You can verify this by watching the Network tab in your browser's developer tools — there are no audio file uploads.