Sound is produced by vibrations. Sound also causes vibrations. By videotaping objects and feeding them through a computer, they can look at the vibrations of the object caused by the sound, and then reverse-engineer the sound that made those vibrations.
It's pretty similar to a laser microphone. There's more research on that online because it's been around for a longer time, so just look up "laser microphone", and you'll get a pretty good idea of what's going on here.
It's pretty similar to a laser microphone. There's more research on that online because it's been around for a longer time, so just look up "laser microphone", and you'll get a pretty good idea of what's going on here.