Convert MP4 to WebM Online

Convert MP4 videos to WebM (VP9 or AV1) for smaller file sizes and better web performance — free, private, entirely in your browser.

Convert MP4 to WebM Free →Free · No signup · No upload

WebM is the modern, open-source video format built for the web. Converting MP4 to WebM using the VP9 or AV1 codec can reduce your file size by 30–50% compared to H.264 MP4 at the same visual quality — making your website load faster and your video stream more efficiently. Resizor lets you convert MP4 to WebM online, right inside your browser, without uploading your file to any server.

The conversion uses the WebCodecs API, which taps into hardware video encoding on your device for fast processing. You can choose between VP9 (wide compatibility) and AV1 (best compression) depending on your needs. The output WebM file is ready for direct embedding in HTML, streaming platforms, or any application that supports the format.

How It Works

Upload Your MP4

Select your MP4 (or any other video format) from your device. No size limit applies.

Choose WebM Output

Select WebM as the output container and pick VP9 or AV1 as the codec for best compression.

Download WebM File

Click Export and download your converted WebM file — ready for the web or any app that supports it.

Why Choose Resizor?

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Fully Private

Conversion runs locally in your browser via WebCodecs. Your video is never sent to any server.

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Web-Optimised Output

VP9 and AV1 WebM files are smaller than H.264 MP4 at the same quality — ideal for web embedding.

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Hardware Accelerated

WebCodecs leverages your device's GPU encoder for fast, efficient conversion.

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Free, No Watermark

Convert as many videos as you want — completely free with no watermarks or registration.

Frequently Asked Questions

Why convert MP4 to WebM?

WebM (VP9 or AV1) offers better compression than H.264 MP4 at the same visual quality, resulting in smaller file sizes. It's the preferred format for web video because it's open-source and supported natively in all modern browsers.

Which WebM codec should I choose — VP9 or AV1?

VP9 has broader hardware support and is faster to encode. AV1 offers even better compression but requires more processing time. For most use cases VP9 is the best choice; use AV1 if you need the smallest possible file and can afford longer encoding time.

Will all browsers play my WebM file?

Yes. WebM with VP9 is supported in Chrome, Firefox, Edge, and Opera. Safari added VP9 support in version 14.1. AV1 support is also growing rapidly.

Can I convert MOV or AVI to WebM too?

Yes. Resizor accepts any video format your browser can decode, including MOV, AVI, MKV, and more, and converts them to WebM.

Is there a file size or length limit?

Resizor has no built-in file size or length limit. Very large files may be constrained by available browser memory on your device, but most videos under 4 GB convert without any issue.

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