How it works

Most online converters upload your file to a server, convert it there, and send it back. mp3bat doesn't. Everything happens in the tab you already have open.

The three steps, on your device

1. Read. When you drop a file, the browser reads it straight into memory on your machine. Nothing is sent anywhere.
2. Decode. The browser's built-in Web Audio engine decodes the audio into raw samples — the same engine that plays audio on the web.
3. Encode. A WebAssembly MP3 encoder, downloaded once and run locally, turns those samples into an MP3 at the bitrate you chose. The result is handed to you as a download from your own browser's memory.

Why this matters

Because the file never travels to a server, there is nothing for us to store, leak, or sell — and nothing to wait on a queue for. It also means the tool can't pull audio from YouTube or other sites for you: that would require server-side fetching, which is exactly the part with legal and security baggage. We convert the file you already have.

Video files work too

For container video — MP4, MOV, MKV, WEBM — mp3bat extracts the audio track using ffmpeg compiled to WebAssembly, which also runs entirely in your browser. The first time you convert a video it downloads that engine once (about 32 MB), then it's cached. Your video is never uploaded, exactly like audio.

The honest limits

Conversion speed depends on your own device, and very large files use your device's memory — big videos take longer and use more RAM, since the work happens locally rather than on a server farm. A higher bitrate also can't restore detail that was never in the source.