1. A system to distinguish foreground motion from background motion in video data, the system comprising: a memory configured to store compressed video data; and a processor block configured to: select, from the compressed video data, a block coding unit (BCU) that potentially includes the foreground motion; determine, without decompression of the BCU, a statistic based on one or more of: a transform-coefficient-magnitude sum of the BCU, a motion-vector-magnitude sum of the BCU, a background mean associated with the compressed video data, and a background co-variance associated with the compressed video data; and determine, based on a comparison of the statistic to a threshold, whether the BCU includes the foreground motion.