v = VideoReader("only-human.mp4");
frames = double(v.read([1 2]))/255;

a = frames(:,:,1,1);
b = frames(:,:,1,2);
h = size(a,1);
N = 100;
d = nan(N,1);
for n=1:N
    b2 = b(n:h,:);
    a2 = a(1:(h-n+1),:);
    c=abs(a2-b2);
    d(n) = mean(c, [1 2]);
end

[~, n_optimal] = min(d);
b_optimal = b(n_optimal:h,:);
a_optimal = a(1:(h-n_optimal+1),:);
c_optimal = abs(a_optimal-b_optimal);
figure
imshow(c_optimal)