Convert MP4 to MKV
Convert MP4 to MKV for free, right here in your browser. The video never leaves your device, however large it is.
- Free
- Runs on your device
- No account
- No limits
One file at a time. The video is converted on your own device, so nothing is uploaded and there's no size limit beyond what your browser can hold.
How to convert MP4 to MKV
- Drop your MP4 file in the box above, or click the box to pick one.
- The first video also fetches the conversion engine, about 7MB, which your browser then keeps. After that it starts straight away.
- The conversion finishes in about a second, because the video itself is copied rather than rebuilt. Then download it.
Why convert MP4 to MKV?
Most people do this because something they are using will not accept MP4 files.
This is usually instant. A MP4 and a MKV normally hold exactly the same video and audio, so the picture is not re-encoded at all, it is moved into a different container. Nothing is lost, because nothing is touched.
The size barely changes, because the video itself is untouched. Only the container around it is different.
About the two formats
MP4: The format everything plays. H.264 video inside an MP4 container is the safest thing to hand anyone.
MKV: The container that holds anything. Popular for films and archives, less welcome on phones and websites.
A video file is a box with codecs inside it, and the box and its contents are separate things. Moving a video into a different box is bookkeeping, and takes a second. Changing the codec means rebuilding every frame, and takes about as long as the video runs. That's the whole difference between the quick conversions here and the slow ones.
Common questions
Is the MP4 to MKV converter free?
Yes, properly free. No paid tier, no trial, no watermark on the result and nothing to sign up for. Put as many files through it as you like, as often as you like.
Are my files uploaded to a server?
No. The MP4 to MKV converter runs inside your browser, on your own machine, so your files never go anywhere. Big ones are fine too, up to whatever your browser can hold.
Does converting MP4 to MKV lose quality?
No. A MP4 and a MKV usually hold the same video and audio, so the streams are copied across and the container is swapped. Not a single frame is decoded or re-encoded, which is why it finishes in about a second and why the result is identical to what you started with.
Why is it so much faster than other converters?
Because there's nothing to upload and, in this case, nothing to re-encode. Sites that upload your file spend most of their time moving it to a server and back. Here the work happens on your own machine, and for this conversion the work is little more than rewriting the file's wrapper.
Is there a limit on the size of the video?
Not one we set, but there's a practical one. The whole file is held in your browser's memory while it works, so very large files can run a tab out of room, and a phone gives up sooner than a computer. Files up to a few hundred megabytes are comfortable on an ordinary machine.