Why convert MP4 to WebM
WebM was built for the open web. Its VP8 and VP9 codecs ship royalty-free on every modern browser, and at equivalent visual quality WebM files are typically 25–35% smaller than H.264 MP4. That difference matters most for landing pages and background-video hero sections, where every kilobyte hits page load time.
Browser compatibility
Chrome, Firefox, Edge, and Brave have supported WebM for over a decade. Safari added support on macOS Big Sur and iOS 16. If you need to cover older Apple devices, ship both formats and let the <video> element pick: a WebM source first for modern browsers, an MP4 fallback for the rest.
VP8 vs VP9
This tool uses VP8 because it's the codec guaranteed to be present in every build of ffmpeg.wasm — VP9 support depends on how the WASM core was compiled. For the file-size and quality differences most users will see, VP8 is fine; switch to VP9 in a desktop editor if you have a specific need for it.