The footage is a buildup to the awakening of the evil and dreaded dragon Smaug, which we see at the very end. Directed by Lord of the Rings maker Peter Jackson, the film stars Martin Sheen as Bilbo Baggins and sees Ian McKellen and Cate Blanchett reprise their roles as Gandalf and Galadriel respectively. It also stars the LOTR originals like Elijah Wood, Christopher Lee and Hugo Weaving.
Interestingly, Star Trek Into Darkness villain and Sherlock Holmes (TV series) hero Benedict Cumberbatch has lent his voice and motione-captured for the dragon Smaug and The Necromancer.
Plot: The Dwarves, Bilbo and Gandalf have successfully escaped the Misty Mountains, and Bilbo has gained the One Ring. They all continue their journey to get their gold back from the Dragon, Smaug.
The Desolation of Smaug is a sequel to Hobbit: An Unexpected Journey and a prequel to The Hobbit: There And Back Again.
Check out the video below.