zooba: What are you talking about? It clearly reads "The Book Thief" and that it's by John Williams (although I guess that doesn't mean that it IS by Williams). There are lots of other "Book Thief" threads already on this site.
Like the original poster said himself in post 2, it's from the album "Tree Of Life" by Audiomachine (track 20 - Day One), which is used in the trailer for the film.
Maybe the youtube user just assumed it was from the original score. Doesn't have to be more complicated than that...