Please help in Shot segmentation with Key Frame selection using Absolute difference

Hello everyone and have a good day.

I would like someone to be able to show me or use a Matlab code to do the following.

1. Segmenting shots of a video, then having a video segmented into several videos.

2. Extract the key-frames.

in point 2, I have a code that downloads from here and works well, but I have a few doubts this is the code (https://de.mathworks.com/matlabcentral/fileexchange/51238-key-frame-extraction-from-video-using-videoreader?focused=3880674&tab=function)

 clc; 

 clear all;

 V = 'Batman2.wmv'; % Video Name

 xyloObj = VideoReader (V); % Using video reader reading video

 % Extracting frames

   T = xyloObj.NumberOfFrames% Calculating number of frames

   for g = 1: T

           p = read (xyloObj, g); % Retrieve data from video

           if (g ~ = xyloObj.NumberOfFrames)

                 J = read (xyloObj, g + 1);

                 th = difference (p, J); % To calculate histogram difference between two frames

                 X (g) = th;

           end
   end
   % calculating mean and standard deviation and extracting frames
   mean = mean2 (X)
   std = std2 (X)
   threshold = std + mean * 4
   for g = 1: T
       p = read (xyloObj, g);
       if (g ~ = xyloObj.NumberOfFrames)
        J = read (xyloObj, g + 1);
        th = difference (p, J);
        if (th> mean)% Greater than threshold select as a key frame

 filename = fullfile ('E: \ Keyframes', sprintf ('frame_% 05d.JPG', g)); % Writing the keyframes
imwrite (J, filename);

       end
       end
   end

 function [r] = difference (f1, f2)
       k = rgb2gray (f1); % Convert into gray scale
       l = rgb2gray (f2);
       f11 = imhist (k); % histogram of data
       f12 = imhist (l);
       diffe = imabsdiff (f11, f12); % Absolute difference of two images
       r = sum (diffe);
   end

My first doubt is:

in the condition for comparison with the Treshold:

 if (th> mean)% Greater than threshold select as a key frame

should be

 if (th> threshold)% Greater than threshold select as a key frame

and my second doubt.

could explain to me, Why in the calculation of threshold = std + mean * 4, the value of Mean is multiplied by 4