About the MP4 to WebM
WebM is the open video format designed for the web, using royalty-free codecs such as VP9 and AV1 with Opus sound. This converter turns MP4 videos into WebM directly in your browser, ready for HTML5 video on websites, web apps and some chat platforms that prefer it. Because WebM can't hold H.264 or AAC, the picture and sound are re-encoded with the best open codecs your browser offers. Preview the result before downloading.
Updated October 2026
How to use the MP4 to WebM
- 1Select an MP4 video.
- 2Press Convert to WebM.
- 3Wait while the video is re-encoded.
- 4Play the WebM preview.
- 5Download it and use it in your web page.
Using WebM on a website
Offer WebM first and MP4 as a fallback in an HTML video element, so each browser picks what it supports best. Short muted WebM loops are a popular, lightweight alternative to animated GIFs.
- video element with two source tags
- WebM first, MP4 second
- Add muted, loop and playsinline for GIF-like loops
Why it re-encodes
WebM only allows VP8, VP9 and AV1 video with Vorbis or Opus sound. MP4 files almost always contain H.264 and AAC, which WebM can't hold, so the tool decodes each frame and encodes it again.
How it works without uploading
Your browser has a built-in video engine (WebCodecs) that phones and computers use to play and record video. This tool uses it through Mediabunny, an open-source media library, to read your file, change it and write a new one, all inside the page. Speed depends on your device: a recent phone or laptop handles a few minutes of HD video comfortably, while long 4K files take longer.
Keeping quality
The encoder uses a high-quality setting by default. For smaller WebM files, compress the MP4 first with our Video Compressor, then convert.
WebM instead of GIF
A few seconds of video as a muted, looping WebM is often a tenth of the size of the same clip as a GIF, with full colour and smooth motion. Trim the clip first with Trim Video, convert it here, then embed it with the autoplay, muted, loop and playsinline attributes so it behaves like a GIF on every device.
Size and quality
VP9 usually makes files 20 to 40% smaller than H.264 at the same visual quality, and AV1 even smaller, but encoding them takes more work, so conversion is slower than playback on older devices. For long videos, keep the tab open and the device plugged in.
Phone and computer
Works in Chrome and Edge on Android and computers; Safari may not encode VP9, in which case the tool explains what happened. To turn the file back, use WebM to MP4, and make a short loop from it with Video to GIF.
Features
- MP4 to WebM in the browser
- VP9 or AV1 video, Opus sound
- Progress bar and cancel
- Preview before download
- No upload
- Free, no watermark
Frequently asked questions
Why convert MP4 to WebM?
Some websites, web apps and tools prefer WebM because its codecs are royalty-free. It can also be smaller than H.264 MP4 at the same quality.
Which codec will the WebM use?
VP9 when your browser can encode it (Chrome, Edge, Firefox), otherwise VP8 or AV1. The sound becomes Opus.
Does WebM play on iPhone?
Safari on recent iPhones and Macs plays WebM in web pages, but some Apple apps don't. Keep the MP4 for sharing with iPhone users.
How long does it take?
Every frame is re-encoded, so roughly as long as the video plays, faster on a strong computer.
Which browsers work best?
Chrome and Edge on computers and Android support the most video formats. Safari 16.4+ and recent Firefox work too, but some codecs, such as HEVC in Firefox, may not be supported there.
Is my video uploaded?
No. It is processed on your own device with your browser's built-in video engine, so private videos never leave your phone or computer.
Can I make a transparent WebM?
Only if the source has transparency, which MP4 videos don't. This tool keeps videos opaque.