How to distinguish an opening sequence from a trailer

What is the difference between an opening sequence and a trailer?

An opening sequence, which is what we will be creating on Sunday, is aimed to set the scene and build tension, to make the audience feel the suspense and the opening should create a narrative enigma, making them gripped and so they will want to see the whole duration of the film, but won't necessarily contain a lot of action. This is usually where the main characters are introduced, and background information to reveal some of the main character's personality, again to help set the scene. An opening sequence also usually displays the titles, as well as the main title during the first 2 minutes of the film. It usually doesn't give too much information away, and doesn't show parts of the film from the middle or the climax, because this is a typical convention of a trailer.

Trailers usually provide the audience with information on the most exciting parts of the film, showing the actors which will be in the film, as well as indicating the genre, but a trailer will not give too much information away about the plot either. The aim is to draw people in before the release date, to encourage people to go and watch it in the cinema. Trailers are broken into small parts, and only display extracts from the film to build tension. They don't often follow a chronological order which is unlike a opening sequence, which again persuades audiences that this film will be worth watching.