NEW YORK: More than half of video ads served are not viewable, largely because many autoplay videos are running below the fold where people cannot see them, new research has suggested.

Vindico, an ad management platform which claims to track 40% of all video ads served on the Web, found that 57% of 2.7bn ads tracked over a two-month period were not viewable.

"The number of ad impressions have exploded, but it's totally manufactured viewing," Vindico president Matt Timothy told Ad Week.

Vindico's research showed that UK business had delivered the most video ads during the research period, claiming 217m views but less than one quarter of these (23%) were viewable.

CBS was in second spot with 195m views and 88% viewability, followed by MSN which achieved 57% viewability. Other sites in the top twenty recorded viewability rates as low as 18% while still claiming millions of impressions.

Timothy said the main reason was the growth in autoplay video running below the fold. "This is a huge priority, and nobody knows what to do about it," he said, adding that Vindico wanted to "shine a light on it" and had developed its own video viewability grading system.

The issue of viewability is not restricted to video ads. Google has recently moved to address the problem in its display ads, announcing it would charge clients only if their advertisements had been seen.

While the company declined to be specific on how many ads on its networks were not currently seen, it did indicate that its prices were likely to rise as inventory supply became more limited as a result.

Google has developed its own technology to assess ad visibility, based on an IAB/3MS standard which regards an ad as being viewable as long as 50% or more of it is visible on screen for at least one second.

"If you are an advertiser and a human being didn't see your ad, then frankly nothing else matters," Neal Mohan, Google's vice-president of display advertising products, told the Financial Times.

"If you are a marketer, why pay if a human being did not see the ad?"

Data sourced from Ad Week; Financial Times; additional content by Warc staff