WebM to MKV converter
Turn WebM files into MKV for free. The conversion runs entirely in your browser, so your videos are never uploaded anywhere.
How to convert WebM to MKV
- Add your WebM files. Drop one or more .webm files on the box above, or tap it to pick them from your device.
- Let it convert. The first video you convert loads the converter once (about 31 MB, then cached). After that it runs on your device; a progress bar shows how far along it is.
- Download the MKV. Press Download next to each file. Nothing was sent to a server, so close the tab and it's gone.
What is a WebM file?
WebM is an open video format made for the web, usually VP8 or VP9 video with Vorbis or Opus sound. Screen recorders and browsers often save WebM.
What is MKV?
MKV (Matroska) is a flexible container that can hold any codec, several audio tracks and subtitles. It is popular for downloads and recordings.
Why convert WebM to MKV?
WebM is great for web pages and open-source players, but iPhones, many editors, WhatsApp and some social networks don't accept WebM. MKV is the better choice for holding many tracks and subtitles in one file; keep in mind phones, TVs, browsers and social networks often won't play MKV.
Will I lose quality?
MKV uses lossy compression tuned so the difference is invisible at normal use. We use high-quality settings by default.
Private by design
Most online converters upload your file to their servers. This one doesn't: the converter itself is loaded into your browser and works offline from there, so your videos never leave your phone or computer.
Questions
Is this WebM to MKV converter free?
Yes, completely free, with no sign-up, no watermark and no daily limit.
Are my WebM files uploaded?
No. The conversion happens inside your browser on your own device. Nothing is sent to us or anyone else.
Can I convert WebM to MKV on iPhone or Android?
Yes, in a modern browser. Phones are slower than computers for video, and very long videos can run out of memory on older phones.
Can I convert several files at once?
Yes. Drop as many as you like; they are converted one after another and each gets its own download button.
Is there a file size limit?
No fixed limit, but your browser has to hold the whole file in memory, so files over about 2 GB may fail.