Originally, WebM, VP9 and Opus support were announced last year in September, but they haven’t shown up until now. Thankfully the latest versions of Edge, found in Redstone builds, does support WebM technologies and the two codecs, though this is still hidden behind an experimental flag.At present, support is only available in desktop beta builds of Windows 10 as there are concerns about battery usage on mobile devices.
To see if this feature is enabled for you, you must first check that you’re running Edge 14.14291 or newer, with that last number being in line with Windows 10 Insider builds versions. Then you need to type about:flags in the address bar and check under Media Source Extensions.
Source Neowin