How and why trailers are trailers are structured this way
The purpose of a trailer is to attract the audience to want to watch it when the film comes out, therefore they need to make the shots they used appealing.
The conjuring trailer is split into three sections. Section one has a slow pace and is where the trailer shows the setting and tone of the film. Then section two is shorter then section one and contains the story element of what the film is about and also shows the disequilibrium. Section three is a faster pace and in the Conjuring shows a montage with cuts and stock scenes, it is also where the story builds to a climax. Conventions of a trailer are the billing block at the end with the production company's involved and a date for when the film will be released.
Trailers are structured in this way because they need to get the story line and the correct information about release dates and who's involved into a specific time limit.
