The video confirms a worldwide release date of November 1 in Europe and October 29 in North America for current and next-generation consoles, including the PS4.
Confirmed last week, Assassin's Creed 4 will be set in the Caribbean in 1715, with players taking control of Edward Kenway, the grandfather of Assassin's Creed 3 protagonist Connor Kenway.
Said to be the biggest Assassin's Creed game yet, it will feature 50 unique locations including the cities of Havana, Kingston and Nassau, as well as fishing villages, smugglers coves, plantations and jungles.
In a first for the series, players are able to explore underwater to search shipwrecks.
With Desmond's story concluded, the player themselves will assume the hero in the present day setting, working for Abstergo and researching Kenway's backstory.
Gallery: First images for Assassin's Creed 4 released:
"With the new hero and new setting we are creating the boldest and most unique Assassin's Creed game yet, while still respecting the pillars of the franchise that have made it such a fan favourite," said Ubisoft CEO Yves Guillemot.
"Assassin's Creed IV Black Flag is based on a true, harsh and exciting part of a legendary era and will thrill longtime fans and newcomers alike."
Details were originally set to be released at 5pm, but several leaks - including news of next-generation console releases - has seen Ubisoft move the official reveal until earlier today.
A PlayStation Vita spinoff, similar to last year's Assassin's Creed: Liberation, will reportedly release alongside Black Flag later this year.
Assassin's Creed 4: Black Flag will release on Xbox 360, PC, Wii U, the PS4 and PS3, both of which will contain 60 minutes of exclusive content.