Drag your audio files in. Get an M4B audiobook out. Your files never leave your browser.
A free, browser-based tool that converts MP3, M4A, WAV, FLAC, OGG, and Opus files into M4B audiobook files with chapters and embedded cover art. All conversion happens client-side via WebAssembly — nothing is uploaded to any server.
🌐 Live: mp3tom4b.com
Other web converters (CloudConvert, Vertopal, Movavi, etc.) upload your files to their servers. mp3tom4b doesn't — the entire conversion runs inside your browser via ffmpeg.wasm. The repo is open source so you can verify that for yourself.
- Drag-and-drop multi-file input
- Each file becomes a chapter, in your chosen order
- Editable chapter titles (auto-generated from filenames)
- Embedded cover art (JPG/PNG)
- Full audiobook metadata (title, author, narrator, year, genre)
- 100% client-side — files never leave your browser
- Free, no sign-up, no ads, no upload size limits
- Next.js 14 + TypeScript + Tailwind CSS
- ffmpeg.wasm for in-browser audio encoding
- Hosted on Vercel
npm install
npm run devOpen http://localhost:3000.
Requires Node 20+.
MIT (see LICENSE).
Built by Burcevski ICT in Amersfoort, the Netherlands.