How to take real-time screen captures and get the average RGB values from every capture?

Question

I have an assigment for school where to copy the Philips Ambilight principle used on LCD TV's to a computer. The assignment is to capture a movie (playing on a computer in windows media player for example).Then divide each screen capture up in 4 zones and calculate each R G and B value.
Next I have to output these values on a serial port into the hardware. The refresh rate should be at least 15 Hz. The output will be a string containing
5 bytes for every channel so 20 bytes(4channels) for each capture. Since it will require a lot of data processing on the PC side I would like to get some input on whether this is doable or not. I was thinking using the directshow lib for this...

Many thanks in advance,