The first video above is the opening cinematic of the game, showing Ellie and a clearly younger Riley at the military camp where they met. Riley is back after being missing for 46 days and...well, I won't spoil it for you.
The second video below is a quick behind-the-scenes video with the voice actors of Ellie and Riley, as well as a quick look at the new mechanics of the single-player content. It's not quite clear whether or not the DLC mirrors the events of the American Dreams comic by Dark Horse, or takes place after it -- though it doesn't start like the first issue, which is sadly the only issue I've read -- but the new feature of being able to turn enemies against each other is a tactic I am eagerly looking forward to exploiting.
The Last of Us: Left Behind DLC hits the PlayStation Network on February 14, for $14.99.