Typically, the fans in your Mac are running all the time. They are just running at relatively slow speeds so they do not make any audible noise. The most common reason for fans to run at full speed is that the air vents are blocked.
Thereof, how do I open Activity Monitor on my Mac?
Start Her Up! One way to start Activity Monitor is to open up Finder, go to the Applications folder, then the Utilities folder, and the shortcut to open Activity Monitor is right there. Another much faster way is if you use Spotlight or Alfred. Then you can just type in the first few letters and up it pops.
What is the Vtdecoderxpcservice?
VTDecoderXPCService is the sandboxing for video content in Lion. All things that are QuickTime related, audio or video, are sandboxed by this service. It just clicked as to what it is. We have iCam for our iPhones. It allows us to remotely view from the webcams on our machines.