Extract M4A Audio from MKV

About MKV and M4A

MKV is the Matroska container — a flexible box that can hold nearly any codec. OBS and most screen recorders write it by default.

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.

Extracting audio from MKV 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.