counting the light frequency in a video

hello can someone suggest a way to count the frequency value in a video similar to this research experiment

https://www.youtube.com/watch?v=LeEBn4ttZZY

https://advances.sciencemag.org/content/6/36/eabd3083/tab-article-info

i was able to find this code though for some reason the frequency value does not change even if i inputed a different video

vidObj = VideoReader( '1.avi' ) ;

nFrames = vidObj.NumberOfFrames ;

tFrame = (1:nFrames) / vidObj.FrameRate ;

ghostCom = zeros( nFrames, 1 ) ;

for fId = 1 : nFrames

grayImage = rgb2gray( read( vidObj, fId )) ;

ghostCom(fId) = sum( grayImage(:) ) ;

end

figure() ; clf ;

set( gcf, 'Color', 'White', 'Units', 'Normalized', ...

'OuterPosition', [0, 0.1, 1, 0.6] ) ;

plot( tFrame, ghostCom/max(ghostCom), 'b' ) ;

set( gca, 'YTick', [0, 1] ) ;

xlabel( 'Time [s]' ) ;

[r] =risetime(ghostCom);

FREQUENCY =numel(r)/60;

sorry i'm new to this thank you in advance for the reply.

[Walter Roberson]

I am not convinced that you can model this as bi-level.

[Luke Abellanosa]

https://www.nejm.org/doi/full/10.1056/nejmc2007800

[Walter Roberson]

That has nothing to convince me that this can be modeled as bi-level.