Why does Quicktime Player HEAT UP?

I have used quicktime player on my iMac with no problem. However, when I use quicktime player on my macbook, it gets HOT. Any answer why?

Heat build-up is directly related to how hard the Central Processing Units (CPUs) are working. Since multimedia viewing can be very CPU intensive—especially for high resolution, graphically complex files—heat can build up faster than when using other, less CPU intensive applications. On the other hand, heat dissipation is directly related the specific design, size, shape, and proper working of the platform in use and so some computer models will tend to retain more heat than others. Always make sure your MacBook is used in a well ventilated area, the fans are turning on and running properly, and that the air vents are not blocked. In some cases, the use of a heat dissipating base or external fan pad may keep your MacBook operating cooler.