Differences between openings and trailers

Film openings are what grab audiences attention and they set the scene for the rest of the film.
Trailers provide audiences with clips from the movie that create suspense. It is a marketisation strategy for audiences to watch their movie.


Thriller Trailer For Dream House (2011)

We can recognize this is a trailer, because the movie 

title is at the end of the clip.

Trailers provide high levels of anticipation and builds up tension. Suspense is when...

1. A state or feeling of excited or anxious uncertainty about what may happen.
2. A quality in a work of fiction that arouses excited expectation or uncertainty about what may happen.

Suspense is an emotion felt by audiences that is felt according to the situation in thriller movies which is why people decide to watch this genre.

Thriller Psycho Opening (1960) 

This is an opening because the title appears through the middle of the scene. 
There is no suspense as this is a narrative lead opening. Only dialogue, establishing shot of where we are and close ups of iconic props. This introduces the audience to the movie and draws them into the story line.