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MKVWebM

Convert MKV to WebM

This free MKV to WebM converter changes your Matroska Video (.mkv) file into a WebM (.webm) file, right in your browser. There is nothing to install, no account to create, and no limit on how many files you convert.

100% private. Your file is processed locally in your browser with WebAssembly — it is never uploaded to a server, stored, or seen by anyone.

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The conversion runs on your own device using ffmpeg compiled to WebAssembly (ffmpeg.wasm), so your file is never uploaded to a server. WebM is best for fast-loading web and HTML5 video, which is the usual reason to convert from MKV.

Why convert MKV to WebM?

  • WebM plays on more devices and apps than MKV, so it is the safer choice for sharing.
  • Re-encoded with VP9, the WebM file is often smaller than MKV at similar quality - handy for the web.
  • Pick WebM when you need a file made for fast-loading web and HTML5 video.

MKV vs WebM

PropertyMKVWebM
Full nameMatroska VideoWebM
ContainerMatroskaWebM
Typical codecH.264 / H.265VP9 / VP8 + Opus
CompatibilityLimitedWide
Relative sizeMediumSmallest
Best forArchiving with multiple tracks and subtitlesFast-loading web and HTML5 video

How to convert MKV to WebM

  1. Add your MKV file

    Drag and drop your .mkv file onto the upload area, or click to browse and pick it from your device.

  2. Start the conversion

    Click "Convert to WebM". Everything runs locally with ffmpeg compiled to WebAssembly (ffmpeg.wasm) - your file stays on your device.

  3. Wait a few seconds

    A progress bar shows the conversion. The first run is slightly slower while the engine loads, then it is cached.

  4. Download your WebM file

    When it finishes, download the .webm file straight to your device.

Frequently asked questions

Is this MKV to WebM converter free?
Yes. It is completely free with no signup, no watermark, and no limit on how many files you convert. It is supported by ads, which keeps the conversion itself free.
Are my files uploaded to a server?
No. The conversion runs locally in your browser using ffmpeg compiled to WebAssembly (ffmpeg.wasm), so your file is processed in memory on your own device and is never uploaded, stored, or seen by anyone.
Will I lose quality converting MKV to WebM?
The video is re-encoded to WebM with a high-quality setting, so the result looks very close to the original MKV. Re-encoding is never bit-for-bit identical, but the loss is minimal.
Will the file get smaller or larger?
Usually smaller. WebM is re-encoded with VP9, an efficient web codec that often beats MKV on size at the same quality.
What is the difference between MKV and WebM?
MKV is Matroska Video (a Matroska container, typically H.264 / H.265); WebM is WebM (a WebM container, typically VP9 / VP8 + Opus). WebM is best for fast-loading web and HTML5 video, while MKV is best for archiving with multiple tracks and subtitles.
How long does the conversion take?
Most files finish in a few seconds to under a minute, depending on length and your device. The first conversion is a little slower while the engine downloads and caches, then later runs start instantly.

Related conversions

MP4 → WebMMOV → WebMAVI → WebMMKV → MP4MKV → MOVMKV → AVI

Need more formats or options? Use the full Change Video Format.