Enhanced code is attached. I upgraded it to use VideoReader and VideoWriter as the routines you used are no longer available in MATLAB.
This turns on Motion JPEG AVI compression. If you want uncompressed changed to 'Uncompressed AVI' in the line marked.
Uncompressed AVI is expected to be larger than the original AVI as the original is likely compressed. Motion JPEG might be smaller than the original AVI: with one or more channels zeroed out, there is less change in the data and that means it can be compressed more efficiently.
Check out the code... I made some improvements.