Book trailers–short promotional videos for new or upcoming books–are all that.
Depending on how you feel or whom you ask, book trailers are (1) a fad, (2) de rigeur, especially for newer writers seeking to build an audience, (3) a new literary/art genre, (4) a marketing tool that can be genuinely valuable to both readers and writers, (5) yet another burden of cost and effort shifted over to the Content Provider, er, author as publishers disengage from promotion and marketing for all but the heaviest hitters, (6) fun, or (7) all of the above.
But if you want to see a short, snappy book trailer that does its job very, very well, see this one for The Native Star, a historical fantasy by Oregon City author M.K. Hobson that will be released in a few months.
Huzzah, say I.