In video ads, view rate is the rate at which an ad is correctly served and rendered. Unlike display ads, video ad view rates are measured with a delayed impression. A video ad entails a higher rate of failure, due to rendering problems, bandwidth constraints, and a greater likelihood of the user abandoning the page before the ad loads. In some cases a video ad is requested proactively to reduce latency.
View Rate = Number of times the first frame is rendered / Number of times the ad won an auction