I wanted to see how little code it would take to control a video from a different device. Open the video page on one computer, open the remote page on another, and use the Play and Pause buttons there.
The video is an HTML5 <video> element. The remote sends a command to a PHP script, which writes it to a small text file. On the video page, jQuery asks the server for a command once a second. If it gets play or pause, it calls the corresponding video method. The query script clears the command after reading it.
There is no direct connection between the two devices, and no streaming video going through my PHP code. The server is just passing a tiny message between two browser pages. It is a deliberately small demo, but seeing a button on one screen change something on another still feels pretty neat.