Here’s an example:
Example Not sure of the technical details but as I understand it has to do with the lack of information available to reconstruct the original image due to lack of information in the original source, lossy compression and/or insufficient bandwidth to carry the information. The macroblock is a 16x16 pixel block used in video compression to carry the image information. When there is insufficient information to construct the detailed image it can show up as one block of color rather than individual pixels.
In the case of “Master and Commander” I mentioned on my system it caused the fog bank to appear as large blocks of distinct shades of grey moving across the screen rather than a gradual gradation of color.
