I've been playing around with the video motion blocks! Work out what is happening on the project page, then look inside to see how it's done! Press m to go to the second activity, and space to finish at any time.
There are two activities, both require the device you are using to have video towards you. You might have to give the webpage (Scratch) permission to access your camera. It works best if your face is about half the size of the stage.