Roku already gave users the ability to stream content from their Android devices to their set top boxes, but now the company is taking things a bit further. Instead of select files, the company will give people to capability to stream whatever is on their screen. We've seen this from Miracast devices, we've seen it from Chromecast, and now we're seeing it from Roku. Update: In fact, Roku is using Miracast to deliver this functionality.
This feature, which is still in beta, will be available to people who own a Roku 3 or a Roku Streaming Stick. It is rolling out to folks starting today, and it should become available to everyone within a matter of weeks.
Screen mirroring will be possible using Android, Windows 8, or Windows Phone 8. On the Android side of things, version 4.4.2 is required, and Roku explicitly points out that custom ROMs are not supported.
Detailed instructions on how to get everything up and running are available on Roku's site.
Source: Roku blog