Animations can stand alone or be superimposed over the live video shots. Each shot has a beginning and an end. It simply butts the end of one shot with the beginning of the next. The order in which the shots are cut together and their length is one of the essential arts of filmmaking - editing. The straight cut is used in a wide range of films from the simplest informational film to the most complex feature film.
Straight cuts can turn a boring home movie into a compelling work of art.
In scriptwriting all transitions from one shot to the next are assumed to be straight cuts unless otherwise noted. Fade to and from Black Most commercials actually begin with a black screen. The first shot fades up from this black screen. The duration of this fade varies from a fraction of a second to as long as two seconds. If you watched this process in slow motion, you'd see that the shot becomes progressively brighter until it is as bright as the shots that follow it.