WebM to MKV Converter
Convert WebM to MKV free — no upload, no signup
To convert WebM to MKV, drop your WebM video into the box below and click Convert. Fylo converts with ffmpeg running inside your browser, so nothing is uploaded and there's no signup or watermark. Repackage WebM into MKV instantly, with no quality loss.
Drop videos here
or tap to browse · paste with Ctrl+V · add many at once
Your files never leave your device
If the video already uses codecs that fit the new format, Fylo repackages it instantly with no quality loss.
Advanced
How to convert WebM to MKV
Add your WebM videos
Drag and drop WebM files into the box or tap to choose them. The converter engine (about 31 MB) downloads once, the first time you convert.
Choose quality (optional)
Balanced quality suits most videos. If the codecs already fit MKV, Fylo repackages the file instead of re-encoding it, with no quality loss.
Convert and download
Click Convert, then download each MKV file or all of them as one ZIP.
Why convert WebM to MKV?
MKV accepts the same VP8/VP9 and Opus streams as WebM, plus extra subtitles and audio tracks — handy for media servers and archives.
What happens when you convert WebM to MKV?
Because WebM is a subset of Matroska, Fylo copies the streams directly. Conversion is near-instant and the file size doesn't change.
How does Fylo convert WebM to MKV?
Fylo reads the WebM with ffmpeg compiled to WebAssembly and writes a straight copy of every stream — Matroska accepts any codec, so nothing is re-encoded. Every conversion to MKV is a lossless repackage, so it finishes in seconds even for large files. Only the first video and audio track are kept, and the original resolution is preserved unless you pick 1080p, 720p or 480p under Advanced.
What's the difference between WebM and MKV?
WebM was announced by Google in 2010 as an open, royalty-free alternative to H.264 for HTML5 video. It's a subset of Matroska restricted to VP8, VP9 or AV1 video and Vorbis or Opus audio. Browser screen recorders and many web tools save WebM by default.
MKV is the Matroska container, an open standard first released in 2002. It can hold virtually any video, audio or subtitle codec, and any number of tracks — so one file can carry several languages, director's commentary and subtitles. WebM is a restricted subset of Matroska.
Learn more: WebM format guide · MKV format guide
| Property | WebM | MKV |
|---|---|---|
| Developed by | Matroska project (open standard) | |
| Introduced | 2010 | 2002 |
| Typical video codecs | VP8, VP9, AV1 | Any: H.264, HEVC, VP9, AV1… |
| Typical audio codecs | Vorbis, Opus | Any: AAC, Opus, FLAC, DTS, AC-3… |
| Plays in web browsers | Yes — Chrome, Edge, Firefox, Safari 14.1+ | Partly (Chrome/Edge for some codecs) |
| Compatibility | Browsers, Android; limited in editors and on iPhone apps | VLC, Plex, Kodi, most smart TVs; not iPhone or many editors |
| Best for | Royalty-free web video, screen recordings | Movies with multiple audio and subtitle tracks |
Frequently asked questions
Is there any difference in quality?
None — the streams are copied byte-for-byte.
Why would I want MKV instead of WebM?
MKV players and media servers sometimes handle .mkv more reliably than .webm, and MKV can hold additional tracks.
Is my WebM file uploaded to a server?
No. Fylo runs ffmpeg, the same engine used by professional video tools, compiled to WebAssembly inside your browser. Your WebM file is read directly from your device and never sent anywhere.
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