Runs entirely in your browser

Your audiobooks,
scored automatically.

M4B AI Mixer layers your own ambient tracks underneath any audiobook, and uses AI to switch the mood as the story moves — calm, tense, dark, upbeat. No file ever leaves your device.

Open the app — it's free See how it works

No signup. No upload. Your .m4b and music stay in your browser's local cache.

AMBIENT TRACKS
Calmmenieldm-obsidian-halls-495840.mp3
Clear
Neutralno track
Upload
Tenseno track
Upload
Darkmenieldm-obsidian-halls-495840.mp3
Clear
Upbeatno track
Upload
Black_cat_poe.m4b
Mood: Auto (by chapter)9:04 / 26:42
HOW IT WORKS

Four steps, zero uploads.

1
Choose your .m4b
Pick any audiobook file from your device. It loads straight into your browser's cache.
2
Add ambient tracks
Upload one instrumental loop per mood — calm, neutral, tense, dark, upbeat.
3
Set it to Auto
The AI reads chapter names and narration cues to detect mood shifts as the story unfolds.
4
Press play
Ambient music fades in and out automatically, ducking under narration the whole way through.
LOCAL-ONLY, ALWAYS

Nothing you load ever touches our servers.

Your audiobook and ambient tracks are stored in your browser's local cache. Close the tab, come back tomorrow — everything's still there. Clear your browser data, and it's gone, exactly as if it had never left your device.

✓No account, no upload — files are read directly from your device.
✓Storage lives in your browser's local cache, not our servers.
✓Works offline once your files are loaded.
WHAT'S NEXT

Built to grow with your library.

The mixer works fully offline today. Here's where it's headed.

COMING SOON
Streaming service connections
Pull ambient tracks straight from your Spotify or Apple Music library instead of uploading loops.
COMING SOON
Playlists
Save and reuse mood-track sets across multiple audiobooks.
COMING SOON
Shared mood presets
Browse and import mood packs built by other listeners for popular genres.

Give your next listen a score.

Open the app — it's free