Difference Between a Title Sequence and a Trailer

Trailer: an overview of the story or the plot that grabs the audience's attention. A  trailer shows the main/good bits  of the action going on and often there is a voice-over to match with the action or plot.. A movie trailer has montage and fast paced editing as well as being able to persuade the viewer to go and watch the movie by making the film seem exciting. It also normally shows the main stars of the film as well, but without revealing their character in the film.

Opening/Title Sequence: An opening sequence is slow paced and leads you into the story line. It does not use montage editing like a trailer. The slow pace  creates an atmosphere, a mood and a tone. An opening sequence must make the viewer feel curious and engaged as if they have questions that they want answered. The soundtrack to an opening sequence helps to create and tone and an atmosphere.