A voice over in a trailer can come from either the main character or someone else narrating details about the film such as its release date or providing context for documentaries. Sound is also important for setting the atmosphere and mood in a trailer using techniques like deep tones for scary scenes and upbeat music for happy moments. Different types of sounds include ambient natural noises, non-diegetic sounds where the source is unknown, and diegetic sounds that come from visible objects in the story.

1. Purpose of a Voice Over and
Sound in a Trailer
By
Munpreet Marbay

2. A voice over is used to help portray the narrative for a film.
This can come in two from, the main character telling the narrative or
someone else.
A voice over:
Gives information about the film, such as the release date.
Commonly used for documentaries or news reports.
Used in radio, television, film making, theatre and production.
Example of a voice over used in a trailer:
http://www.youtube.com/watch?v=34x6m-ahGIo

3. Sound is used to help tell the narrative of a trailer.
Can be used to set the atmosphere, eg deep sound is used depict a
scared and sad mood, where as a upbeat sound is used to depict
happiness.
Different types of sound:
Ambient sounds: sounds in the natural in the surrounding
Non Diegetic Sound: Sounds which are used but you cannot see the
source of the sound, this could be the narrators voice.
Diegetic Sound: Where the source of the sound can be seen, this
could be sounds made by objects in the story.