Ads on youtube is either paid per click or per view. The one that's per click is self explanatory.
The click per view will only make money when either half of the ad or 30 sec of it is watched, whichever comes first.
It's up to the advertisers which one it is, be it CPV (Cost per view) or CPC (Cost per click) and you have no way to know which is which.
The least you could do it watch half/30 sec of the ads at least so you would still contribute to the CPV one.