TrueView is built on the promise that you'll only pay when someone chooses to watch you

TrueView is a YouTube video ad format that gives the viewer options, the most common of which is the ability to skip the advertisement after five seconds. 

There are four types of TrueView ads:

• In-stream ads allow viewers to skip the pre-roll ads after five seconds. Sponsors pay only for ads that are viewed in their entirety or until 30 seconds have elapsed. In-stream ads are suitable for short or long video content. 
• In-slate ads allow viewers to among several sponsors' ads or opt for commercial breaks interspersed through the video content. Sponsors pay for ads that are selected by the viewer. In-slate ads are suitable for videos that are at least 10 minutes long. 
• In-search ads appear in YouTube search results when the viewer's search is related to the ad's keywords. Sponsors pay for ads that the viewer begins to watch. 
• In-display ads are legacy formats that appear in the YouTube promoted videos overlay, in video suggestions and related videos, and in Google's Click-to-Play format.  Sponsors are charged when viewers opt to watch an ad. 

According to Google, the owners of YouTube, eight out of ten viewers prefer TrueView to other in-stream video ad formats. The company also maintains that because viewers can skip ads or select the ads they want to watch, the advertiser saves money and reaches a more targeted audience. 

According to VideoNuze.com, an online video analysis and news webstite, the abandonment rate for skippable pre-roll ads was 18 percent lower than the rate for ads that don't offer that option. The site also reported that almost 50 percent of viewers watch pre-roll ads to the end, even if they have the option to skip the commercial.