Convert MKV to WebM
Convert MKV files to WebM entirely in your browser. Google's royalty-free web video format — VP9 + Opus, ~20–35% smaller than MP4. Drop your MKV below — vexo runs ffmpeg-wasm locally, nothing is uploaded.
Drop your video here
or choose a file from your device
Max 200 MB per file. Conversion runs in your browser.
Every conversion runs entirely in your browser. Your video never leaves your device.
About MKV → WebM
Why convert MKV to WebM?
WebM with VP9 + Opus is 20–35% smaller than MP4 at the same perceived quality, ideal for HTML5 <video> served from your own site. MKV is excellent for archiving with subtitles and multiple audio tracks, but few mobile devices or browsers play it directly. vexo extracts the primary video and audio into a clean MP4-compatible stream.
About MKV
MKV (Matroska) is the most flexible video container in common use — it can wrap virtually any video codec, any audio codec, multiple subtitle tracks and chapter metadata in a single file. That makes it the default choice for archives, encodes from physical media, and downloads that need to ship subtitles. The catch: very few browsers, iOS devices, smart TVs or editors open MKV directly. Converting to MP4 gives you the same video stream in a container the rest of the world actually plays.
About WebM
WebM was designed for the open web. VP9 typically produces 20–35% smaller files than H.264 MP4 at the same visual quality, and Opus is the best general-purpose audio codec available. Every modern browser (Chrome, Firefox, Safari 14+, Edge) plays WebM natively. vexo encodes WebM with VP9 + Opus, and falls back to VP8 + Vorbis automatically if the wasm bundle lacks VP9.
What you're converting between
A short primer on both formats so the trade-offs are obvious before you hit Convert.
MKV
SourceMatroska · introduced 2002
MKV (Matroska) is the most flexible video container in common use — it can wrap virtually any video codec, any audio codec, multiple subtitle tracks and chapter metadata in a single file. That makes it the default choice for archives, encodes from physical media, and downloads that need to ship subtitles. The catch: very few browsers, iOS devices, smart TVs or editors open MKV directly. Converting to MP4 gives you the same video stream in a container the rest of the world actually plays.
Strengths
- Holds anything — video, audio, subtitles, chapters
- Open, royalty-free container
Trade-offs
- iOS, most browsers and TVs cannot play it directly
- vexo keeps only the primary video and audio track when converting
- Subtitles and secondary audio are not preserved
WebM
TargetWebM · introduced 2010
WebM was designed for the open web. VP9 typically produces 20–35% smaller files than H.264 MP4 at the same visual quality, and Opus is the best general-purpose audio codec available. Every modern browser (Chrome, Firefox, Safari 14+, Edge) plays WebM natively. vexo encodes WebM with VP9 + Opus, and falls back to VP8 + Vorbis automatically if the wasm bundle lacks VP9.
Strengths
- Smaller files than MP4 at the same perceived quality
- Royalty-free, open codec
- Native playback in every modern browser
Trade-offs
- Older video editors (iMovie, older Premiere) may reject it
- Some social uploaders and legacy players prefer MP4
- Slower to encode than MP4 in ffmpeg-wasm
Popular conversions
Each link below opens the converter pre-tuned for that conversion.
Supported formats
MP4 is the safest default for web and mobile playback. WebM gives the smallest files for modern browsers. GIF is for short, soundless animations.
WMV, FLV and other legacy/streaming formats are not supported in this version. Please convert those to MP4 first using a desktop tool.
| Format | Input | Output | Notes |
|---|---|---|---|
| MP4 | Yes | Yes | H.264 + AAC, broadest compatibility |
| MOV | Yes | No | Apple/QuickTime container; convert to MP4 |
| WebM | Yes | Yes | VP9 + Opus, smaller than MP4 |
| MKV | Yes | No | Container; convert to MP4 or WebM |
| AVI | Yes | No | Legacy container; convert to MP4 |
| GIF | Yes | Yes | No audio, short clips only |
| WMV | No | No | Not supported |
| FLV | No | No | Not supported |
Frequently asked questions
Your videos never leave your device
vexo is a static page. Every conversion runs inside your browser via ffmpeg compiled to WebAssembly. There is no server-side processing, no upload, no temporary file, no cache. When you close this tab, every file is gone.
- No account required.
- No server processing. Your videos stay on your device.
- No caching, no Service Worker, no IndexedDB persistence.
- The conversion engine (ffmpeg-wasm) is fetched from a public CDN and cached by the browser; no personal data is sent.