Convert MP4 to MKV
The same video in the container collectors trust — repacked instantly on your own device, zero quality loss.
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.
MKV is the container serious media collections standardize on: it holds nearly any codec, carries chapters and multiple tracks, and plays in the players enthusiasts actually use — VLC, Plex, Kodi, mpv. Moving an MP4 into MKV brings it in line with a library built on that standard.
Because MKV happily carries MP4's H.264 and AAC as-is, this conversion is a pure repack: the streams are copied bit-for-bit into the new container in seconds, with zero re-encoding and zero quality loss — even for large files. Everything happens in your browser; nothing uploads.
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
Is MP4 to MKV really lossless?
For the common codecs, yes — H.264, HEVC, VP9 video and AAC or MP3 audio all copy into MKV unchanged, and the result panel confirms when the copy happened. Unusual audio codecs are re-encoded at high quality instead.
Why do media libraries prefer MKV over MP4?
Flexibility — MKV carries any codec, multiple audio and subtitle tracks, and chapters, without MP4's format restrictions. For a curated library played through VLC, Plex, or Kodi, that headroom matters.
Will the MKV play on my TV or phone?
Many modern TVs and Android players handle MKV; iPhones and some smart TVs do not without a player app. MP4 remains the compatibility king — MKV is the choice when your playback stack is built for it.
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.