About Opus and M4A

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.

M4A is AAC audio in an MP4 container — the default format of the Apple ecosystem and most streaming services. AAC compresses more efficiently than MP3, so the same bitrate sounds a little better.

Converting Opus to M4A is lossy. 192 kbps is transparent for most listeners on most material; pick 320 kbps if you want the ceiling, or drop lower when small files matter more than fidelity.

How the conversion works

This tool runs FFmpeg — the same engine behind most media software — compiled to WebAssembly, entirely in your browser. Your 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 your first conversion, cached by the browser afterwards. Once it's loaded, everything works offline.