Convert MKV to MP4
Most MKV files hide perfectly good MP4-compatible video inside — we just repackage it. Instant, lossless, and entirely on your device.
Drop your video or audio here
or
MP4, MOV, WebM, MKV, AVI, MP3, WAV and more — any size, no upload
🔒 Files never leave your device — everything runs in your browser.
Here is the secret about MKV files nobody tells you: the video inside is usually already H.264 — exactly what MP4 uses. The problem is only the container, the "box" the video sits in, which many players, TVs, and editing apps refuse to open. For those files, ConvertUno does not re-encode anything: it moves the untouched video and audio into an MP4 box. That is why the conversion often finishes in seconds with literally zero quality loss — and you will see a "lossless" badge when it happens.
When an MKV does carry an exotic codec, the tool detects it and falls back to a proper hardware-accelerated re-encode at high quality. Either way, nothing is uploaded: OBS sessions and large downloaded files convert right on your machine — how large depends only on your device's memory, not on any limit of ours.
How it works
- Drop your file
Any common format, any size. Nothing is uploaded — the tool runs in your browser.
- Convert
Compatible files are repackaged instantly with zero quality loss; others are hardware-transcoded at high quality.
- Download
Your converted file is ready on your device — nothing to wait for, nothing to delete from a server.
Frequently asked questions
Why is my MKV to MP4 conversion instant?
Because your MKV already contained MP4-compatible video (H.264/AAC), so ConvertUno simply repackaged it without touching the picture — a "remux". The output is bit-identical in quality to the source. You will see a lossless badge on the result when this happens.
Will subtitles inside my MKV survive?
Embedded subtitle tracks are not carried over yet — the output focuses on the primary video and audio. Extract subtitles with a desktop tool like MKVToolNix if you need them; subtitle support is on our roadmap.
How large an MKV can this handle?
We impose no limit — the file never uploads anywhere and is read straight from your disk. The practical ceiling is your device's free memory, since the converted result is assembled in RAM before download: files up to a gigabyte or two are comfortable on typical machines, and remuxes are fast since nothing is re-encoded. Support for writing huge outputs directly to disk is on the roadmap.
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.