What is the difference between a film trailer and a film opening?

We had a class discusion about the differences between film openings and trailers and these are the differneces we found;

Opening
• Enigma codes.
• Establishing shot for the settings.
• Action shot – character in role doing things.
• Variety of shots.
• Titles- imaginative and creative.
• Music- does it fit its genre
• Music- does it fit the mood.

Trailer
• Provides a summary of plot – plot outline.
• Character roles.
• Short, varied clips- from the entire film.
• Clear idea of equilibrium/disequilibrium/new equilibrium.
• Music sells the film- Gives excitement.