My own definition of what a teaser trailer is.

After watching 4 or 5 different types of teaser trailers, I have come to the conclusion that it should be 1 minute - 1.30 minutes, however the minimum amount of time given should be 40 seconds. The teaser trailer should reveal parts of the film which could be a shared frame of reference if there is a previous film or t.v episode. The audience should find or see something which they will want to know more about as the film release date comes ever nearer.

By the end, we should have an idea on something which could happen, as writing with subtitles should ask questions, however, they should not be answered.