What are the matlab codes needed to analyse a video (not real time) for rgb shape tracking?

Hello. I have created an .avi video on matlab consisting of moving rgb squares. I now need to analyse this video and track red coloured squares using bounding box. However, i don't know how to start and how to use the video for analysis. The problem is that I cannot process the video and apply functions like getsnapshop when i use the function VideoReader in the beginning.