How Can I draw histogram of all video's frames?

I am trying to run this code in parallel to read each video frame , take the direction gradient , and substracting histogram of current frame and next one, then show the result histogram

I have get this error message:(Dot indexing is not support for variable of this type)

What should I fix in the following code?

function [] = parfun()

tic

vid = VideoReader('002.mp4');
vid.CurrentTime = 0;


vidlen = vid.NumFrames;

    
parfor i = 1:vidlen 
   temp = read(vid,i);
   temp2 = read(vid,i+1);
   
   gradframe = imgradientxy(temp);
   gradframe2 = imgradientxy(temp2);
     
   tohisto = histogram(gradframe)- histogram(gradframe2);
   figure
   histogram(tohisto); 
 
end
toc
end

[Geoff Hayes]

@Roaa Alnafea - please copy and paste the full error message so that it is clear which line of code is throwing the error.

[Roaa Alnafea]

Error using parfun (line 13)

Dot indexing is not support for variable of this type

Answer 1

[Benjamin Thompson]

Use readFrame to read a single video frame from a VideoReader object. But note that reading frames from a VideoReader is not parallellizable on its own, since the frames come from a sequential video file source and it is usually not possible to know exactly where in the file future frames will start. Plus with lossy compression algorithms future frames usually depend on a past frame.

You could, however, load a set of frames in a sequential manner and then perform processing on the set using parfor. You will have to choose the size of the set based on the number of cores available and memory limits.