The app's new video sharing capability only works with video that was captured using the iPhone and saved to the photo library; it does not work with other video content stored on the phone. Shareable videos can be accessed by tapping on the "Play on Roku" button and selecting content from the newly included video menu.
Streaming video works with multiple versions of the Roku, including Roku 3, Roku 2, Roku HD, Roku LT, and the Roku Streaming Stick.
Roku is a free app for the iPhone that can be downloaded from the App Store. [Direct Link]