Convert WebM to MKV
Last updated: June 1, 2026To convert WebM to MKV, drop your WebM file into the converter above, then download the MKV result. It's free, needs no sign-up, and there's no watermark. Conversion runs in your browser with on-device FFmpeg, so your files never leave your device.
Why convert WebM to MKV?
Convert WebM to MKV free, right here in your browser. Because WebM is actually a restricted slice of the Matroska format, the underlying VP9 or VP8 video and Opus audio already fit inside an MKV container — so this is effectively a lossless rewrap, not a re-encode. That keeps quality pixel-identical and finishes fast. Everything runs locally through FFmpeg compiled to WebAssembly, so your file never uploads anywhere. No sign-up, no watermark, no size cap from a server.
- A media server like Plex, Jellyfin, or Kodi skips or mis-handles your WebM downloads — rewrapping them as MKV makes them index cleanly with proper titles, chapters, and subtitle tracks.
- You want to merge external subtitle files or extra audio tracks into one video. MKV happily carries multiple subtitle, audio, and metadata streams, whereas WebM is far more limited.
- A smart TV, set-top box, or hardware player (Nvidia Shield, many LG and Samsung sets) recognizes .mkv natively but ignores .webm, so changing the container makes the file just play.
WebM vs MKV
WebM · WebM (VP9)
WebM is an open, royalty-free format designed for the web. VP9 video gives smaller files than H.264 at similar quality and is ideal for embedding directly on a site.
MKV · Matroska Video
MKV (Matroska) is a flexible open container that can hold many video, audio and subtitle tracks in one file. It's popular for archiving, but doesn't play natively in many browsers or on some TVs.
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Convert video to MP4, WebM, MOV, MKV, GIF or MP3.
Open Video ConverterWebM to MKV — frequently asked questions
Will converting WebM to MKV reduce the video quality?
No. WebM's VP8/VP9 video and Vorbis/Opus audio are valid Matroska streams, so the tool copies them straight into the MKV container without re-encoding. The result is bit-for-bit identical in quality — there's no generational loss because nothing is recompressed.
Is my video actually uploaded anywhere during conversion?
Never. The entire conversion happens inside your browser tab using FFmpeg compiled to WebAssembly. Your file is read from disk, rewrapped locally, and offered back as a download — it does not touch our servers or any third party, which is why even large or private clips stay completely on your device.
Why is WebM to MKV so much faster than other video conversions?
Because it isn't a real conversion in the heavy sense — it's a remux. The codecs already match what MKV allows, so FFmpeg just changes the wrapper instead of decoding and re-encoding every frame. That's why even multi-gigabyte files finish in seconds rather than minutes.
How do I convert WebM to MKV?
Drop your WebM file (or several) into the converter, confirm MKV is selected as the output, click convert, then download the MKV file. The whole thing takes a few seconds.
Is this WebM to MKV converter free?
Yes — it's completely free with no watermark and no sign-up required.
Is it safe to convert WebM to MKV here?
Yes. Conversion runs on-device with FFmpeg compiled to WebAssembly, so your WebM file is never uploaded to a server.
Can I convert multiple WebM files at once?
Convert one WebM file at a time — finish one, then drop in the next.
Does it work on mobile?
Yes — the converter runs in any modern browser on phones, tablets and desktops.