Basically, the software it takes small movements in a video that are invisible to the human eye — the subtle color change caused by blood pumping through someone's face, or the slight pulsing of an artery under his skin — and amplifies them until they're plainly visible. This is basically like having a superpower:
It's easy to imagine what you could do with tech like this: an optimist might point to medical applications; a realist could imagine scarily advanced security cameras.
Either way this is unsettling, and exciting, stuff. I mean, imagine a pair of Google's glasses that let you see other peoples' heartbeats? The researchers say they'll be releasing code soon, so it's not outside of the realm of possibility. You can watch the full video below: