Convert MKV to MP4
Turn MKV videos, such as OBS recordings, into MP4 files that phones and editors open: your files stay on your device, nothing is uploaded, and it is free with no account.
Drop an MKV video here
One video up to 2 GB. MKV and WebM work too.
Starting UFO Web…
The work happens in this tab. Nothing is uploaded.
How it works
Choose an MKV video or drop it on this page. MOV and WebM videos work too.
Keep the video as it is, which is fast and loses nothing, or choose H.264 so it plays everywhere. H.264 takes longer, because every frame is encoded again.
Download the MP4. Your original file is not changed.
Questions
Are my videos uploaded anywhere?
No. The work happens inside this browser tab, so your videos never leave your device and no server sees them. Closing the tab clears them from memory.
What carries over into the MP4?
The first video and sound track. H.264, HEVC, VP9 and AV1 video and AAC or Opus sound are copied without re-encoding. Other sound, such as MP3, FLAC or Vorbis, is converted to AAC or Opus. Subtitles and extra sound tracks are left out. Dolby Digital and DTS sound can be converted only where the browser can decode it; otherwise the MP4 has no sound and the page says so.
What are the limits, and which browsers work?
One video up to 2 GB and 4 hours when it is copied, or 30 minutes when it is encoded again as H.264. Only the first video and sound track are kept. It works in Chrome and Edge, in Firefox 130 or newer on a computer, and in Safari 16.4 or newer, using the browser's own video codecs (WebCodecs). Firefox on Android cannot do it yet. If your browser cannot handle a video, the page says so as soon as you add it.
The same file engine is in the UFO apps for Android and Windows.