Updated July 2026
About this tool
WebM is the video format of the open web: royalty-free VP8/VP9 video with Opus audio, natively supported by Chrome, Firefox and Edge for HTML5 video embeds. At comparable visual quality, VP9 typically produces files 20–40% smaller than H.264 — a real difference for hero videos, background loops and anywhere bandwidth matters.
This tool transcodes your MP4's H.264 video to VP9 (with VP8 available as a compatibility fallback) and the audio to Opus, which at 96–128 kbps is transparent for most content. For websites, ship it with a fallback: a <video> element with the WebM <source> first and the original MP4 second lets modern browsers take the smaller file while Safari and older devices still play.
Conversion runs in a Web Worker in your browser — videos are never uploaded.
Frequently asked questions
Why convert MP4 to WebM?
For the web. WebM with VP9 typically compresses 20–40% smaller than H.264 at comparable quality, uses royalty-free codecs, and is the native choice for HTML5 video in Chrome, Firefox and Edge. Smaller files mean faster page loads and less bandwidth — which is why WebM is standard for hero videos and animation loops.
What is the difference between VP9 and VP8, and which should I use?
VP9 is the newer codec — better compression at the same quality — and the right default today. VP8 exists as a fallback for old browsers and some embedded WebViews. Use VP9 unless you specifically target legacy environments.
Why is the audio converted to Opus?
WebM pairs with Opus (or the older Vorbis), not AAC. Opus is arguably the best general-purpose audio codec available: at 96–128 kbps it is transparent for most content, so the audio typically sounds identical while taking less space.
Does WebM play in Safari?
Mostly, but not universally — Safari added WebM support late and older iOS versions still refuse it. For websites, the robust pattern is a <video> element with a WebM <source> first and an MP4 fallback second: modern browsers take the smaller file, everything else still plays.