Film Trailer Information

A trailer or preview is an advertisement or a commercial for a feature film that will be exhibited in the future at a cinema. The term "trailer" comes from their having originally been shown at the end of a feature film screening. The purpose is to appeal and drawn in an audience by presenting extracts of the film to them in places such as the internet, television, the radio and the cinema etc. The length is generally short and approximately 2-4 minutes long, depending on whether it is a teaser trailer (which are shorter). 
The content are extract clips from the film, and are usually what are considered the 'best bits' without revealing the whole storyline, which is a mistake many film distributors make, meaning the audience do not feel like they need to see the film as they have already seen the best bits. This has influenced my own film trailer as I suggested that the ending sequence will leave a looming cliffhanger, which appeals to an audience as they will want to know the ending. 
The production form may vary depending on the maker, some may be; animated, 3D, digital or hand-drawn. 

Examples of effective trailers from a range of genres: