For several years, Google has been analyzing television set-top box data to measure audience response to specific TV ads. This paper presents how similar techniques can be applied to online video advertising on YouTube. As more and more video programming is made available online, it will become increasingly important to understand how to engage with online viewers through video advertising. Furthermore, we find that viewing behavior is even more effected by specific video ad creatives online than it is on TV. This suggests that online viewing can become a valuable source data on viewer response to video ad creatives more generally.