MP4 to MKV converter
Convert MP4 videos to MKV right in your browser — free, private and fully offline. Drop a MP4 file, pick MKV, and choose a re-encode for maximum compatibility or a fast lossless remux. Nothing is uploaded and there is no file-size limit; the conversion runs entirely on your own device.
Open MP4 to MKV converter →Convert MP4 to MKV online — free and private
This MP4-to-MKV converter runs entirely in your browser on the WebCodecs engine. Your video never leaves your computer — no upload, no account, no watermark and no file-size paywall — and it keeps working offline once loaded. MP4 and MKV use different codec families, so the picture has to be re-encoded. The tool picks the most widely-playable codec the MKV container supports and that your browser can encode.
How to use MP4 to MKV converter
- Add your MP4 video — Drag the MP4 file onto the drop zone, or click to browse and pick it. The tool reads its container, resolution and codecs and shows them straight away.
- Choose MKV — Pick MKV as the output, then choose Best compatibility for a re-encode that plays everywhere, or Fastest to copy the existing tracks where the MKV container allows it.
- Convert and download — Watch the progress, preview the result in the player, and save the .mkv file.
Frequently asked questions
Is my MP4 video uploaded to a server?
No. The conversion runs inside your browser using your own device's hardware, so the video never leaves your computer. There is no size limit and it works offline.
Will converting MP4 to MKV lose quality?
A small amount, yes. MP4 and MKV store video in different codecs, so the picture must be decoded and re-encoded. The tool encodes at a high quality setting to keep the loss hard to see.
How long does it take?
A lossless remux takes seconds whatever the length. A re-encode runs about as fast as your computer's video hardware allows — a few minutes for a long clip is normal.
Which other formats can it convert?
The same tool reads MP4, M4V, MOV, MKV, WebM and MPEG-TS, and writes MP4, WebM, MKV and MOV. AVI, WMV and FLV cannot be opened — no browser can decode those containers.