This was one of the assignments in After Effects. Take the static background image, insert a massive crowd in front of it using only a handful of students in front of a green screen, and use the virtual camera to create a parallax effect.
I think it works pretty well. The guy in the red shirt stands out, but other than that the effect works. It’s the same thing they do in movies like Lord of the Rings to make a huge army of orcs with only a few actors in make up rather than hundreds.