mkv → mp4
MKV to MP4, repackaged not re-encoded
Get an MKV to play on a TV, a phone or in an editor that pretends the format does not exist. Usually finishes in seconds with the picture untouched.
Files are processed on your device · nothing is uploaded, stored or logged
How it works
Pick your file. The browser reads it straight from disk. There is no upload progress bar, because there is no upload.
The encoder loads once. A WebAssembly build of FFmpeg, around 30 MB, downloads the first time you use the site and stays cached afterwards.
Your processor does the work. Everything happens in this tab, at roughly half of real time on a modern laptop.
Save the result. The finished file is assembled in memory and handed to your downloads folder.
MKV is a container, not a codec
This trips people up constantly. MKV does not describe how the video is compressed — it describes how the pieces are boxed together. Inside a typical MKV sits H.264 or H.265 video, which MP4 is perfectly happy to hold.
So the conversion is usually not a conversion at all. The streams are moved from one box to another, which takes seconds and changes nothing about the picture.
MKV is popular because it carries things MP4 handles poorly: multiple audio tracks, embedded subtitles, chapter markers. Those extras are what get lost in the move, not the quality.
What does not survive
Subtitle tracks embedded in the MKV are dropped, and only the first audio track is kept. If your file has an English and a Japanese track, you will get whichever came first. That is a limit of MP4 itself, not of this tool.
MKV files often carry several audio tracks. To pull one out as a separate file, use extract audio.
Common questions
Will the picture look worse?
No, in the normal case. The video stream is copied across without being decoded, so it is identical to the original.
What happened to my subtitles?
MP4 does not carry them the same way. Extract the subtitle file separately before converting if you need it.
Why did mine re-encode?
Some MKV files hold codecs MP4 cannot store, such as VP9 or FLAC audio. The tool detects this and re-encodes automatically.
Is there a file size limit?
No enforced limit, but browsers run out of memory somewhere around 500 MB to 1 GB depending on your machine.