Microsoft announced in a blog post that it's going to finally adopt the open source VP9 codec in Windows 10's Edge browser, as well as other open source audio and video codecs in the future.
Microsoft was initially reluctant to adopt the previous-generation VP8 codec, preferring the proprietary h.264 video codec instead. At the time, there was a battle between who's going to support what, and Google and Mozilla sided with VP8 while Apple and Microsoft chose h.264. Apple usually tends to go its own way, regardless of what everyone else does, but if Microsoft had adopted VP8 back then as well, VP8 and VP9 may have already had wide hardware support.
For now, Microsoft will support software decoding for VP9, but where the hardware exists (typically on some mobile chips), hardware decoding will also be supported for more efficient video playback. For software decoding, Microsoft recommends more powerful PCs. This is also why, for now, the VP9 support will be enabled only as an experimental flag in the Edge browser.
Microsoft Edge will support VP9's adaptive streaming using Media Source Extensions in the initial implementation, which will be detectable using the MediaSource.isTypeSupported() API. Microsoft said it is also working on future support for VP9 for media tags and local playback.
The company is also considering support for other codecs such as OGG, Vorbis and Opus. Opus, especially, tends to be paired with VP9 in the WebM container format, which YouTube currently uses by default.
Microsoft recently became part of the Alliance for Open Media, where companies such as Mozilla, Google, Cisco, Intel, Amazon and others will work on improving upon VP9, Daala and Thor to create a single open source and royalty-free video codec that everyone can use without limits.
The VP9 video codec will be supported in the Edge browser in the Windows 10 Insider Preview builds soon and will later come to a more stable build, as well.