Best bet? Ask the author "How did you do that?"
Some beginners think this is done in realtime but most is done in "post production". Example at https://www.youtube.com/watch?v=8qhja5opFPo
Bob
I've been watching a few videos for Let's Race gaming (commonly found on SpeedRunsLive or SomethingAwful) and was just wandering for this video: https://www.youtube.com/watch?v=6RFPVIe0awk if anyone could tell me how the person would have edited this video together. In particular, how did they make the synchronized smiley faces that talk when they talk, and the health bar next to the faces with their names in it. Much appreciated!!!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic