Microsoft Edge team today detailed the support for WebM container format and the VP9 video and Opus audio codecs that was added starting with EdgeHTML 14.14291. Microsoft decided to add support for these formats to simplify building interoperable websites, and to provide an alternative format for compressing 4K video content. VP9 codec is actually developed as part of the WebM Project by Google. Web developers can make use of these new formats in Edge using Media Source Extensions (MSE) to adaptively stream video content. Even the Windows Web Apps will be able to use WebM streams containing VP9 and Opus.
Software decoding consumes significantly more power when compared to hardware encoding. But, there is no way for apps to confirm whether the hardware acceleration is supported on the current device. So, Microsoft has decided to put VP9 behind an experimental flag in Microsoft Edge, and have provided a default setting for it that automatically enables VP9 when hardware acceleration is detected. VP9 is not supported on Windows mobile SKUs at this time.
Read more about these new formats here.