Understanding the difference between a Trailer and a Opening sequence

The main difference between the two is that a Trailer is designed for the purpose enticing the audience to watch the film by showing the "best" bits of the film usually very short, snap shots of usually the main actors in the best scenes of the film but they only show key scenes as not to give much away. Where as an Opening sequence is the audiences welcoming to the film. It's designed to "lead the audience by the hand" and slowly settle them into the world of the film. This is why opening sequences are scene as an art in it's own right because in my opinion it's probably the most important scene in the film because without it the audience is supposed to just get the movie straight away.

The conventions of a trailer include the use of fast short shots to almost bombard with information. Somehow enticing the audience to come to the cinema and watch it when it comes out. A linked to the previous point the details like age rating, release date, what actors star in it and weather there are any more in the trilogy.