Blurring most of each video frame except for ROI - X,Y coordinates known (Python)

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I need a way in Python to take a roughly 30 second clip and blur out most of it, except for a circular ROI which would contain the normal video quality. For each frame of the clip I know what the x,y coordinates of the ROI need to be. I also need for the ROI to be circular. What is the best way to go about doing this?