NEW YORK: Ten-second mobile video ads have greater brand appeal and persuasion potential for Millennial audiences than 30-second ones, but the reverse is true for an older audience, new research has shown.

A study – Multiscreen Video Best Practices – from the Interactive Advertising Bureau in partnership with Millward Brown Digital and Tremor Video looked at responses to two ad executions, one of ten seconds, one of 30-second reports, for three unique digital video campaigns across smartphones, tablets, and desktops; a total of 1,800 people were surveyed.

This found that, as well as preferring shorter ads, Millennials were particularly sensitive to mobile ad clutter. Mobile video advertising for this audience "should be well targeted, relevant and enjoyable to help maximize its potential impact," the report said.

Longer ads had a particular role, as the study found that, overall, audiences agreed that 30-second mobile video advertising was better for communicating new or complex information.

When asked about how much new information was provided by an ad, 73% of those surveyed gave high marks to 30-second ads, compared to 68% for ten-second spots.

Screen sizes were another factor influencing understanding, with larger screens better at conveying a moderately complex message: 73% said ads viewed on tablets were good at delivering new information, compared to 65% for smartphones.

Tablet video was also found to be more engaging with older, 35-54 year old consumers who described ads on these devices as more "interesting," "unique," and "involving" than those on other platforms.

"The conventional wisdom is that all video ads on mobile screens must be short in order to resonate with audiences," said Joe Laszlo, Vice President, Industry Initiatives, IAB.

"Our research shows that for some demographics and some advertising goals this doesn't hold up – these findings are critical in creating the next generation of multiscreen video advertising."

Not only do video ads need to be developed with smaller mobile screens in mind they should also be created in such a way that they can be effectively shortened from long formats without losing their ability to communicate.

Data sourced from IAB; additional content by Warc staff