Does CutFast upload my file?
No. Conversion runs locally in your browser — your file stays on your device.
MKV to MP3 Converter
Convert MKV → MP3 locally in your browser with CutFast (WebCodecs). Remux when possible, transcode when needed — no uploads, no installs.
Frequently asked questions
What’s the difference between remux and transcode?
Remux copies streams into a new container (fast, no quality loss). Transcode re-encodes (slower, quality depends on settings).
Why can’t I select some codecs?
Codec availability depends on your browser’s WebCodecs encoder support and the target container.
Which browsers are supported?
CutFast requires WebCodecs for the fast path. Latest Chrome / Edge are recommended.
Will converting reduce quality?
Remux does not. Transcoding may — you can raise the quality preset to reduce loss.
What formats do you support?
Common inputs include MP4/WebM/MOV/MKV. Outputs include MP4/WebM/MOV/MKV plus MP3/AAC/WAV.