Microsoft Edge team announced the support for WebM container format and the VP9 video and Opus audio codecs into the Edge Browser starting with EdgeHTML 14.14291. that was added starting with EdgeHTML 14.14291. These are available to websites that use Media Source Extensions (MSE) to adaptively stream video content.
You can manage the settings for VP9 and Opus by navigating to http://about:flags in the address bar in the latest Windows 10 insider Previews.
This change will be available in stable releases starting with the Windows 10 Anniversary Update. Support for these formats to simplify will help in building interoperable websites and also providing an alternative format for compressing 4K video content.
Windows Web Apps (built on the same Edge APIs) can also use WebM streams containing VP9 and Opus. VP9 is an efficient open-source video codec developed as part of the WebM Project by Google.While Opus is the primary audio codec paired with VP9 in the WebM specifications.
Read more about them here.