Conventions of a Teaser Trailer

I have reasearched a few teaser trailers and there are some key similarities. A teaser trailer is a small grouping of clips from a new film, TV show or game which is used to alert the audience that the product is coming soon and giving them a little insite into what they are going to watch or play.
The conventions are:

• A teaser trailer is from 30-90 seconds long
• A teaser trailer has small amounts from the actual film, TV show or Game as footage as the trailer is to tease the audience
• A teaser trailer is also released much earlier than the actual trailer

This is the teaser trailer for 'The Dark Knight Rises'. It is 1min 36 seconds long and so is just outside the usual teaser trailer length. It has little footage from the film and was uploaded on the 18th July 2011. This is much earlier than the actual trailer which was released on the 20th December 2011.