You've seen a lot of flashmob videos, but this one doesn't have much flash, and it's not really a mob, just a beautiful performance for those lucky enough to be in Sabadell, Spain, when they recorded it. A Babelfish translation from the video link says:
So ignore the fact that it's an ad and enjoy the music. -via reddit
In 130º anniversary of the creation of Sabadell Bank we have wanted to pay a tribute to our city with the campaign “Som Sabadell”. This is flashmob that we realised like final finishing touch with the participation of more than 100 people of the Orquestra Simfònica of the Vallès and the choirs Lieder and Amics of l'Òpera and the Chorale Belles Arts.
So ignore the fact that it's an ad and enjoy the music. -via reddit
Brava!