Difference Between Trailers and Film Openings

Film openings and trailers vastly differ to one another, they are composed, produced and presented very differently, their intent and purposes contrast each others...

The purpose of film trailers is to hook the audience, they make the film appear as enticing, dramatic and thrilling as they can, this is done through heavy amounts of editing, and the shots are usually cut so that they fit a sequence of music, which will usually build tension and lead to a cliff hanger climax.
Usually a montage editing technique is used, portraying a series of the film's most significant and dramatic scenes, which will effectively excite the audience and hold their attention. This technique will also allow for the basic plot of the film to be outlined so the audience can decide whether they believe they will enjoy the story line.

Conversely, film opening's purposes are predominately to give the audience an introduction to the film and story line, this will be done by conveying the location, the protagonists and antagonists. The genre/mood of the film is usually conveyed through establishing shots, location, lighting and music. Film openings often create tension and mystery, hoping that this will cause the audience to want to continue watching.