Compress MKV files
Big container, big files: shrink an MKV on your own device and walk away with a small MP4 every app can open.
Drop your video here
or
MP4, MOV, WebM, MKV, AVI and more — any size, no upload
🔒 Files never leave your device — everything runs in your browser.
MKV is the container of choice for OBS recordings, long captures, and high-quality rips because it survives crashes and holds anything — but that flexibility comes with bulk, and with the eternal problem that plenty of players, TVs, and platforms refuse to touch it. When an MKV needs to be shared or uploaded, it usually needs to become smaller and it always needs to become an MP4.
ConvertUno does both in one pass, on your own hardware: the video is re-encoded to your exact target size and remuxed into standard MP4 (H.264 + AAC). Multi-gigabyte inputs are fine — nothing is uploaded, so the only cost of a big file is the encoding time, which hardware acceleration keeps close to the video's own duration.
How it works
- Drop your file
Any common format, any size. Nothing is uploaded — the tool runs in your browser.
- Pick your target
Use the presets above — this page's defaults are tuned for compress mkv — or type any size.
- Download
Your converted file is ready on your device — nothing to wait for, nothing to delete from a server.
Frequently asked questions
Why is MKV so common for recordings if nothing plays it?
Because it is crash-safe — an interrupted MKV recording stays recoverable where an MP4 could be corrupted, which is why OBS defaults to it. It is a great capture format and a poor sharing format; this tool is the bridge between the two.
My MKV has multiple audio tracks — what happens to them?
The compressor keeps the primary audio track and encodes it into the output. Multi-track selection is planned for the full converter suite; today, the main track is what travels with the video.
Can it handle a 5 GB recording session?
Yes — there is no input limit, since the file is read directly from your disk without any upload. Long sessions take roughly their own duration to encode with hardware acceleration.
Is my file uploaded to a server?
No. ConvertUno runs entirely in your browser on your own device. Your file never leaves your computer or phone — there is no upload at all.
Is it really free, with no watermark?
Yes. Processing happens on your device, so serving you costs us almost nothing — no watermark, no account, no file-size limit, no daily quota.