Determine the color of certain pixels in a video

I'm using Python 3.6. I am a beginner with OpenCV. I'm trying to determine the color of 4 pixels at certain coordinates in each frame of a video. When all 4 pixels are white, I have to print the time of that frame. When one or more of the pixels then change color to something other than white, I have to print the time of that frame (so that I end up with the start and end time of the pixels being white). So I need help with 2 things: 1. How do I read each frame of the video? 2. How do I determine the color of pixels at those specified coordinates? Thanks!