What are trailers?

The film industry is a huge part of the media and constantly developing and growing, as technology is. A trailer or preview is an advert for a film that will be later shown at a cinema. Trailers are shown
• At the cinema before a different film
• As a television advert
• On the internet
Trailers consist of shots and footage from the film that is being advertised, so are usually produced after the film itself. Due to the much shorter length of film trailers, the footage has to be selected very carefully and is often the most funny / exciting / thrilling parts of a film. They are often called teaser trailers because they show interesting parts of a film without revealing any of the spoilers.
The scenes in a trailer do not necessarily always appear in chronological order or the order that they appear in the actual film. The purpose of a trailer is to make the film look as good as possible to the prospective audience so that they will go to a cinema to watch it, therefore making profit for the production company everyone involved in the process of making the movie.
Most trailers have a three-act structure similar to a film – the beginning, where equilibrium is balanced, the middle, where equilibrium is disrupted and the last stage is usually a montage of memorable shots from the movie. Voice overs, songs, orchestral scores and speedy transitions are common in trailers. If a film features a popular actor then there will most likely be many shots of them in the trailer.
Other things that appear in trailers are:
• A cast run of the list of main actors in the movie, and sometimes the director & producer
• A concluding Billing Block, which lists the cast and crew
• Studio production logos, and logos for the production company and distributor
• A green band or red band, showing the MPAA rating of the film