Convert MP4 to WebM

How to convert MP4 to WebM

1. Drop up to 10 MP4 files on the box above, or click to choose them. Nothing is uploaded.
2. Your browser converts them one after another, with a progress readout for each file.
3. Each WebM downloads as soon as it is ready, with the same name as the original.

You do not need an account, and converting video does not use any of your monthly image allowance.

What the converter does to your video

• Video: re-encoded to VP9, the codec most websites use for WebM. If your browser cannot encode VP9, it uses AV1 or VP8 instead.
• Audio: kept, and re-encoded to Opus, the standard audio codec for WebM.
• Size and length: the same resolution and running time as the MP4.
• File size: the converter aims for the same video bitrate as your MP4, and VP9 gets more picture out of those bits than H.264, so the WebM usually comes out smaller. In our tests it was 14% to 33% smaller.

It is a re-encode, not a rewrap: MP4 usually carries H.264 video and AAC audio, which a WebM file cannot hold, so both tracks are encoded again.

Why your video never leaves your device

The conversion runs in your browser tab, using the video encoder built into the browser (the WebCodecs API). Your file is read from your disk, converted in the tab and saved back to your downloads. It is never sent to Mochify or anyone else, which is why there is nothing to sign up for and nothing to delete afterwards. Most online converters upload your file to a server first; for client footage, unreleased product videos or anything under NDA, that difference matters.

Which browsers can convert

Desktop Chrome and Edge convert reliably. Firefox (version 130 and later on desktop) and Safari (version 26 and later) also include the browser video engine this page uses. Firefox on Android does not. If your browser cannot encode WebM, the page tells you instead of failing silently.

Long or high-resolution clips use a lot of memory, because the whole file is held in the tab while it converts. A desktop or laptop handles large files best.

Using your WebM on a website

Serve the WebM first and keep the MP4 as a fallback, so every browser gets a file it can play:

<video autoplay muted loop playsinline preload="metadata" poster="/images/poster.jpg">
  <source src="/video/hero.webm" type='video/webm; codecs="vp9, opus"'>
  <source src="/video/hero.mp4" type="video/mp4">
</video>

The browser plays the first source it supports. Only have a WebM? The WebM to MP4 converter makes the MP4 fallback. Our MP4 to WebM guide covers VP9 against AV1, browser support and how video choices affect Core Web Vitals.

Converting MP4 to WebM without a converter

• FFmpeg (free, Windows, Mac and Linux): ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 33 -b:v 0 -c:a libopus output.webm. A lower -crf gives higher quality and a bigger file.
• HandBrake (free, Windows, Mac and Linux): open the MP4, set Format to WebM in the Summary tab, and pick VP9 as the video encoder.
• VLC: Media > Convert / Save with the "Video - VP80 + Vorbis (Webm)" profile. That writes the older VP8 codec, so the files are larger than VP9.