Runs on your machine, not our servers
Load a WebM or MKV file, hit convert, then choose whether to keep your original file untouched or overwrite it. Everything happens locally in your browser tab — nothing is uploaded.
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Drop a file here, or use the button below
Your file is read only inside this tab. Nothing is uploaded anywhere — the "server" for this step is your own CPU.
FFmpeg (compiled to WebAssembly) demuxes the Opus track and re-encodes it as MP3.
The original video stream is copied — not re-encoded — into a fresh MKV alongside the new MP3 track. Download either file when it's done.