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MP4WebM

Convert MP4 to WebM

This free MP4 to WebM converter changes your MPEG-4 Part 14 (.mp4) 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 MP4.

Why convert MP4 to WebM?

  • Note: WebM has narrower support than MP4 - convert only when a specific app or workflow needs it.
  • Re-encoded with VP9, the WebM file is often smaller than MP4 at similar quality - handy for the web.
  • Pick WebM when you need a file made for fast-loading web and HTML5 video.

MP4 vs WebM

PropertyMP4WebM
Full nameMPEG-4 Part 14WebM
ContainerMPEG-4WebM
Typical codecH.264 + AACVP9 / VP8 + Opus
CompatibilityUniversalWide
Relative sizeSmallSmallest
Best forSharing and playing almost anywhereFast-loading web and HTML5 video

How to convert MP4 to WebM

  1. Add your MP4 file

    Drag and drop your .mp4 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 MP4 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 MP4 to WebM?
The video is re-encoded to WebM with a high-quality setting, so the result looks very close to the original MP4. 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 MP4 on size at the same quality.
What is the difference between MP4 and WebM?
MP4 is MPEG-4 Part 14 (an MPEG-4 container, typically H.264 + AAC); WebM is WebM (a WebM container, typically VP9 / VP8 + Opus). WebM is best for fast-loading web and HTML5 video, while MP4 is best for sharing and playing almost anywhere.
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

MOV → WebMAVI → WebMMKV → WebMMP4 → MOVMP4 → AVIMP4 → MKV

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