The first 24 hour video.
Time to get you happy on.
#24hoursofhappy
Updated 12/14/13 to add the celebrity cameos.
To coincide with the single release, the website 24hoursofhappy.com was launched featuring a visual presentation of "Happy" advertised as being "the world's first 24 hour music video". The video consists of the four-minute song repeated with various people dancing and miming along. Williams himself appears 24 times on the hour, and there are a number of celebrity cameos including Odd Future (1:48pm),Steve Carrell (5:08pm), Jamie Foxx (5:28pm), Ana Ortiz (5:32pm), Miranda Cosgrove (5:40pm), JoJo (6:16pm), Kelly Osbourne (1:28am),Magic Johnson (5:36am), Sérgio Mendes (10:32am) and Jimmy Kimmel (11:48am). The minions from Despicable Me 2 make several appearances throughout the film, including one scene at 3:00am, in which Pharrell and the minions dance in a movie theatre that is playing the scene from Despicable Me 2 in which "Happy" appears. The site allows users to navigate to various points in the 24-hour timeframe, including all 360 four-minute segments and each hourly segment with Pharrell. [Source]
