How can I plot variation of light intensity of a pixel or a small ROI over time in a video?

Hi, I am trying to detect light variation of small zone or a pixel of a video and plot it over time. This is one step of a bigger project which is extraction of heart beat signals from recorded videos of beating heart. Could you please help me address my issue. Thanks in advance.

[Yash Ubale]

Is your main motive is to find the heart beats per second? If it is so, then follow the answer to a similar question below.

How to find heart beating pattern? - https://www.mathworks.com/matlabcentral/answers/301563-how-to-find-heart-beating-pattern?s_tid=answers_rc1-2_p2_MLT