If the user chooses a sports clip, then your video message should have some contextual narrative or visual approach that links your brand to sports.

The same goes for news, movies, music-- whatever.

The cost of developing and producing a contextually relevant short form pre-roll is about the same as what you're paying to have your agency cut down a :30 to a :15.

So produce a pool of them that you can use on multiple sites. Otherwise, you're just filling up inventory with lean back creative designed for passive viewing.