Extract Opus Audio from MP4

About MP4 and Opus

MP4 is the standard video container on the web. Extracting its audio track is a quick way to turn a music video, lecture or recording into a listenable file.

Opus is the newest codec here and the most efficient — it outperforms MP3, Vorbis and AAC at low bitrates, which is why WhatsApp, Discord and WebRTC all use it. Support is universal in browsers, patchier in older hardware.

Extracting audio from MP4 re-encodes only the audio track — the video is discarded, so even long files finish quickly.

How the conversion works

This tool runs FFmpeg — the same engine behind most media software — compiled to WebAssembly, entirely in the browser. The file is read locally, converted locally and saved straight from memory; nothing is ever uploaded, which also means no queues and no server-side file size limits.

The converter itself is a one-time ~31 MB download on the first conversion, cached by the browser afterwards. Once it is loaded, everything works offline.