It's not an official promotional video, although the clip is an impressive one nonetheless.
Youtube user NikoBellicSerbia assembled this seven and a half minutes trailer from all of the footage which has been made available via the official promotions, including the ones that showed in the UK and Japan. Duplicate clips were removed, and what was left has been re-cut into what seems to be the order the scenes would appear in the film, though this is only a guess on the editor's part. Some additional music was added to help with some of the transitions, but the sound is still pretty choppy due to the differentiations in the multiple sources.
The Hobbit tells the story that comes before The Lord of the Rings. In some ways, The Lord of the Rings is a sequel to The Hobbit, but from another perspective, The Hobbit is a prequel to The Lord of the Rings, as the original author J.R.R. Tolkien added lots of material to the original Hobbit story in a set of documents now known as 'the appendices.' It's this modified, and greatly expanded version of the story that Jackson is adapting, using the same shooting locations, styles, and some of the same actors from his adaptation of the LOTR trilogy.
Originally intended to be two films, it has been split into a trilogy all its own. The first movie is The Hobbit: An Unexpected Journey, which will cover the events of the book from Bilbo's introduction to Gandalf in Bag End to Bilbo's encounter with Gollum and The One Ring. Some of the clips in the above uber-trailer seem like they may be from the second and third film, but mostly it's from the first.
The official synopsis for the film is thus:
The Hobbit follows the journey of title character Bilbo Baggins, who is swept into an epic quest to reclaim the lost Dwarf Kingdom of Erebor, which was long ago conquered by the dragon Smaug. Approached out of the blue by the wizard Gandalf the Grey, Bilbo finds himself joining a company of thirteen dwarves led by the legendary warrior, Thorin Oakensheild. Their journey will take them into the Wild; through treacherous lands swarming with Goblins and Orcs, deadly Wargs and Giant Spiders, Shapeshifters and Sorcerers.
Although their goal lies to the East and the wastelands of the Lonely Mountain first they must escape the goblin tunnels, where Bilbo meets the creature that will change his life forever... Gollum.
Here, alone with Gollum, on the shores of an underground lake, the unassuming Bilbo Baggins not only discovers depths of guile and courage that surprise even him, he also gains possession of Gollum's "precious" ring that holds unexpected and useful qualities... A simple, gold ring that is tied to the fate of all Middle-earth in ways Bilbo cannot begin to know.
The Hobbit: An Unexpected Journey hits theaters Dec 14 , 2012. The follow up film, The Hobbit: The Desolation of Smaug, follows on Dec 13, 2013. The third and final Hobbit film, The Hobbit: There and Back Again hits on July 18, 2014.