Follow this steps.
1. Play video and start recodring using "Start record" button and then click "Security" of police man shape.
2. Select "Mosaic" in the left side combo box and drag mouse in the area to add mosaic effect.
3. In the rapidly changiing scene, slow down the play speed or play frame by frame and follow the motion.
For more, refer to following Youtube link!
Here is the applied video example.