The 20 minute long video starts with Phil Collinson describing how it was when David took over from Chrisopher Eccleston for the second series in 2005. He said "By the time The Christmas Invasion transmitted, we were terribly confident we had the best man for the job".
The importance of the companions, especially the return of Donna, and their families are discussed.
At the end, Jaqueline King admits that she couldn't continue watching Doctor Who after David had left, because it was too emotional to watch another Doctor and Phil Collinson added David "took the show to a level it had never been to before and never since."
The video can be watched here