In one video, two men in jeans and hoodies take a rocket tube to a rooftop and fire it. From another angle, we see three Syrian tanks in a row. The middle one takes a huge hit, emits a sheet of orange flame and burns away; a smoldering figure jumps from the tank and runs off as bullets smack the ground around him.

Another video opens with a long take of a busy traffic area, full of buses and pedestrians, some of whom seem to be soldiers. One bus suddenly erupts from within, and dozens of people collapse. The videotaker repeatedly...