I have noticed high CPU utilization in a number of applications (except mplayer) which read from the embedded webcam on my laptop. Bizarrely CPU utilization varies proportionately to the level of illumination present. I know that that high CPU usage has nothing to do with rendering the video, as I have written a simple app using the OpenCV library to simply grab frames from the webcam, and cpu usage is still high. I think that mplayer might be using my GPU (and the other apps aren't), but since its not an issue with rendering, I dont think this explains anything.

Cheese

Low light ---> ~12% CPU

Bright Light ----> ~63% CPU

Camorama

Low light ---> ~7% CPU

Bright Light ----> ~30% CPU

Opencv C++ library, (display in a single highgui window)

Low light ---> ~13% CPU

Bright Light ----> ~40% CPU

(same test on windows 7, 4-9%)

Mplayer

No problem, 1-2% regardless of light levels

Note: If all I want't to do is capture a feed from my webcam I would use mplayer and forget about it, but I'm developing an application which uses the OpenCV to capture a video feed among other things, performance is important.