Video streams like RTSP streams are unfortunately not natively supported by a web browser. Since Playr runs 100% in a browser, that means that Playr does not support video stream playback out-of-the-box.
But there are third party services out there that will convert a RTSP stream to a web page, which can then be used in a Playr Web Page app. One of those services is called rtsp.me. So check them out if you need to display a video stream in your Playr channel.