MP4 to WebM Converter

Free, no sign-up. Your video never leaves your device.

Video quality
Frame size

MOV and MKV with H.264 and AAC are repackaged into MP4 without re-encoding — fast and lossless. Everything else is re-encoded in your browser, which is slow: a minute of video takes from tens of seconds to a few minutes. 720p means the short side of the frame is 720 pixels.

Usage statistics

We count page views and operations. A random cookie identifies a browser profile; after sign-in its activity is linked to your account. Your last IP and its observation date are visible only to the site owner and kept for up to 90 days. Daily counts are kept for 90 days, and inactive profiles are removed after 90 days. Formats, outcomes, error codes, and size and time ranges are counted separately. File names, contents and metadata stay on your device. Turning this off deletes the current browser profile.

How to convert MP4 to WebM

  1. Click the box above or drag your MP4 files onto it — you can add many at once.
  2. Wait while your browser processes the video — nothing gets uploaded. Progress is shown as a percentage.
  3. Download each WebM separately or grab them all in one ZIP file.

Why use this converter

  • Your video stays with you

    Conversion runs on your device. Your video is never uploaded, so nobody but you can see it.

  • VP9 and Opus

    Video is encoded to VP9 and audio to Opus — royalty-free codecs every modern browser supports.

  • Pick quality and size

    Choose the quality and frame size — from original down to 480p — so the video loads faster on your site.

  • Many files at once

    Add several videos at a time and download them one by one or as a single ZIP.

Frequently asked questions

Why convert MP4 to WebM?

WebM is an open video format for the web. Websites use it as an alternative to MP4: at the same quality, VP9 usually gives a smaller file than H.264.

Which codecs are used?

VP9 for video (VP8 or AV1 if your browser can't encode VP9) and Opus for audio.

Will WebM play on an iPhone?

Recent Safari and iOS versions play WebM, but older devices and some apps don't. If you need maximum compatibility, stick with MP4.

Why does it take a while?

Re-encoding video is heavy work, and it happens right on your device. A minute of video takes from tens of seconds to a few minutes, depending on resolution and your computer. Progress is shown as a percentage.

How do I make the file smaller?

Choose “Medium” or “Low” quality and a smaller frame size — 720p or 480p. 720p means the short side of the frame is 720 pixels: for a vertical video that's the width.

Which browsers does it work in?

Up-to-date Chrome, Edge, Firefox and Safari: video is encoded with the browser's built-in codecs (WebCodecs). If your browser lacks a codec, the file's row will tell you.

Is it safe?

Yes. Only the converter itself is loaded from the site; your video is processed in your browser and never sent to a server.

More converters

  • WebM → MP4

    Web videos and screen recordings, as MP4 for any device.

  • MP4 → MP3

    The soundtrack of a video, as an MP3 for any player.

  • MP4 → GIF

    A short video, as a GIF for chats and websites.

  • MOV → MP4

    iPhone and camera videos, as MP4 for any device.