lot of extra ! include a inline video commentary -lrb- which put up a tiny frame in the lower left hand corner of the screen let you see the people as they actually watch the episode -rrb- on some of the episode . not all the episode have commentary . David Tennant do commentary on several episode ! deleted scene ! David Tennant 's Video Diaries -lrb- around a hour -rrb- . Billie Piper also do a short video diary in the Makeup Trailer . child in need special help people from the US understand the start of the Christmas special .