Convections of an opening scene

The purpose of a film opening is too grab the audiences attention straight away, so they are hooked into the film and want to carry on watching it as they are intrigued. The opening of the film will also show the genre of the film and who the protagonist is and the antagonist.
The timing convections in most film openings are about 2-5 minutes long. However some films start with acting first and when that's done it then goes into the titles. 
In the film openings it usually sets the scene, so we know the location of the film.
It always introduces the key characters within the first few minutes of a film, e.g. in action films, you are always introduced to the hero and the villain straight away.
 the film opening usually introduces pre plot, so it kind of lets the audience in to what the film is going to be about.
Key credits are big thing at the  opening of a film, it tells us what company it is part of, logos and who the director of the film is.
It sometimes starts with equilibrium, so a big event will occur straight away, so this hooks people into the film.