Windows 10 Insider Preview Build 10576 is out and it comes with support for media casting.
Now with Edge, you can send videos, pictures, and audio to any Miracast and DLNA enabled device in your home. Which has support for YouTube videos, Facebook photos, and Pandora songs. But protected content is not supported, so no Netflix, Hulu, etc.
Other changes in this build include Xbox beta app voiceover recording and search and purchase functionality, a fix for the Xbox beta RAM usage issue which popped up under specific circumstances, and Hyper-V performance improvements.