This is research and quotes from the book Lisa Kernan, Coming Attractions: Reading American Movie Trailers (University of Texas Press, 2004):
‘trailers are film paratexts. As Gérard Genette has characterised them”
‘Trailers offer audiences ‘concise, direct-address cinematic texts that serve as both attractions and as a form or persuasion’
‘most trailers have in common a few generic features: some sort of introductory or concluding address to the audience about the film either through titles or narration, selected scenes from the film, montages of quick-cut action scenes, and identifications of significant cast members or characters.’
‘trailers commonly utilize codes of voice-over narration, sound and sound overlapping, music, graphics, and most importantly, editing, or montage.’