The eagle eyed will notice from the video that the doors have buttons. These were disabled on other Tube trains a number of years ago. The driver will have control of the doors, but will close them if the train has to stay on the platform for any length of time, keeping the cool or warm air in. So if that happens new passengers will need to press the button to re-open the door.
More about the air conditioned trains can be found on TfL's website and if you want to see the current one in action it will be running from Wembley Park to Watford from 2nd August. The roll-out on the Metropolitan Line will be complete by 2011. We'll start seeing them on the Circle and Hammersmith & City lines from 2011. Then the District line will get the next lot in 2013 and all trains will be on the network from 2015.
Update - the point about door buttons had a number of us wondering why the door buttons were disabled. So I asked TfL who said "LU removed passenger door activation across all lines in 1998 to speed up station dwelling times, as the Underground was getting busier. The new S-Stock doors are opened by the driver but after 45 seconds they close to keep cooled air in during summer, or warm air in during winter. The door can be reopened by pressing the in-carriage button, but ultimately the driver has complete control of the doors and can override them."