YouTube are the creators of this new ad format TrueView that lets users skip over ads that they aren't interested in. The way the TrueView ad unit operates is that it begins playing then you'll notice a five second countdown timer once thats complete an arrow shall appear leaving you skip the remainder of the ad if your not interested and take you back to the content you initially wanted to view. Advertisers are initially happy about the latest results as they only pay if the user doesn't hit the "skip" button so in theory everyone watching the ad has a general interest in the ad. Since this is a new system it is unknown how affective the technique shall be since TrueView is new to a user they might be engaged to see what happens and not press the skip button at all. Also worth noting is that all ads aren't going to be in this format as the original format is still available and the choice between each format is up to the advertiser.
VIA: Tech Crunch