As noted above there are only two options: directly read the website of the movie (jippo solution) or ask the api of TheMovieDB (Ivek23 solution).
The last may be the most consistent, at the end of the file seem returns the url of the trailer:
"videos":{"results":[{"id":"533ec657c3a368544800078b","iso_639_1":"en","iso_3166_1":"US","key":"R1hZNHPVVAQ","name":"Trailer 1","site":"YouTube","size":360,"type":"Trailer"}]}}
But I don't see this easy and ... ¿how many times see you the trailer of a film that you have seen? (and to decide which movie see never trust in a commercial trailer) ;-)