According to April 2015 research by Google, marketers remain concerned about paying for video ads that aren't seen. Paying more for larger ad sizes could help boost viewability, says the report.

Out-of-home (OOH) advertising produces the best combination of reach and consumer activity of all media. Consumers reported action responses, purchases, online searches, brand-related social media activity, etc., within a half-hour of exposure to OOH advertising 22% of the time.