Support VP9 video codec when not hardware-accelerated
Edge supports the WebM VP9 encoding in MSE but only when accelerated, or if the end-user modifies about:flags. This means that sites using WebM VP9 but not H.264 cannot rely on playback in Edge, as most computers do not yet have hardware VP9.
For sites like Wikipedia that avoid H.264 due to licensing policy, this leads to less efficient workarounds or lack of media usage. We would love to deploy Edge-compatible VP9 if it were usable. An opt-in API for JS would be acceptable.
Brion Vibber commented
This is now implemented in the Web Media Extension package along with Ogg, but not yet installed by default - https://blogs.windows.com/msedgedev/2017/12/05/introducing-web-media-extension-package-ogg-vorbis-theora-support/