Motion vector calculation

I am doing a project in Image processing "Grouping similar images in a video using Motion vectors and segmentation". In that, a video is seperated into frames(334 frames), and all the frames are divided into 8 * 8 blocks. With Image analyst and Kye taylor`s help, i managed to divide all the frames into 8 * 8 blocks. Now, I need to calculate the motion vectors for each block using Block matching concept. I used the following code

R=10;N=8;
for x = 1:N:height-N
for y = 1:N:width-N
MAD_min = 256;
mvx = 0;
mvy = 0;
for k = -R:1:R
for l = -R:1:R
MAD = 0;
for u = x:x+N-1
for v = y:y+N-1
if ((u+k > 0)&&(u+k < height + 1)&&(v+l > 0)&&(v+l < width + 1))
MAD = MAD + abs(f1(u,v)-f2(u+k,v+l));
end
end
end
MAD = MAD/(N*N);
if (MAD<MAD_min)
MAD_min = MAD;
dy = k;
dx = l;
end
end
end
xblk = floor((x-1)/(N+1))+1;
yblk = floor((y-1)/(N+1))+1;
mvx(xblk,yblk) = dx;
mvy(xblk,yblk) = dy;
end
end

I referred it somewhere here.

f1- anchor frame, f2-target frame. I think the code is working and the motion vectors are found. But, I want to know how the motion vectors are calculated here. Can anybody give the description for this code?

[shriya patil]

isn't it taking too long time for execution process??