Roku announced this morning it’s rolling out screen mirroring functionality in beta for “a select number” of Windows 8.1 and Android devices. The feature will allow these users to quickly mirror content on their devices to the big screen, including videos, apps, websites and more. The functionality is only being supported in the company’s Roku 3 or Roku Streaming Stick (HDMI Version), the Roku blog post notes.

Screen mirroring via a hardware dongle or device is becoming a popular way to connect smartphones, tablets and PCs to TVs in order to easily share content you have saved on your device, or other things want to show off on the big screen – like funny videos, gameplay, Facebook content, and more. But Roku’s announcement leaves out of a big chunk of the market for now: it doesn’t mention anything about when this support will come to OS X (Mac) users or iOS devices.

For now, those users will have to be content with the other options Roku already supports, like the “Play On Roku” feature in its mobile app, which lets you send music, photos and videos saved on your smartphone to the TV via any Roku player. Roku also offers apps like Netflix and YouTube which you can launch using your smartphone or tablet app and play on your TV via the Roku 3 or Streaming Stick.

The new beta release of screen mirroring is rolling out starting today to supported Roku devices, and will reach all customers within the next few weeks, the company says.

We’ve known that Roku was working on delivering mirroring support to its devices, having last year teamed up with Broadcom to bring Miracast video mirroring to its video streaming devices. (Broadcom noted the partnership at Mobile World Congress in February.) The company doesn’t confirm in its announcement today what technology is being used, but David Zatz points out that Firefox Video Casting is also now supported in beta, which suggests more possibilities.