Window shopping on YouTube or TV?

During the playoffs, I saddled up at a bar in Palo Alto and somehow struck up a very bizarre conversation with a very bizarre entrepreneur. Strangeness aside, he had an interesting idea: He was looking for technology where a viewer of a video on YouTube or cable TV could point, click, or touch to buy items that are in videos. So, say I’m watching the Yankees and Mariano Rivera is pitching, and I wanted his jersey, it would be pretty cool to just buy it with a touch or click. Does this tech already exist?