Via GamesRadar, this is the leaked first trailer for Assassin's Creed IV: Black Flag.
In the trailer, a grizzled pirate describes Captain (and assassin) Edward Kenway.
"There was a time I thought myself the deadliest scourge of these seas," the pirate says. "But this man..."
We then see Kenway hacking, slashing, and doing his assassin thing. The trailer ends on a silhouette of Kenway.
At the end of the trailer, we see a slide saying Assassin's Creed IV will be out October 29 and that it's "also coming on next-gen consoles." Logos on the bottom: PS3, PS4, Xbox 360, Wii U, PC.
UPDATE: The trailer has been taken down. Here's the pertinent screencap:
We'll have more on Assassin's Creed IV this Monday.