Facebook is urging marketers to rethink how they go about creating and measuring mobile video ads because consumers only watch ads that grab their attention, reward their time and are immediately relevant.

According to the social media giant, users scroll through its mobile news feed 41% faster than on desktop, which means advertisers should measure the effectiveness of ads in terms of results rather than seconds.

"It's true that this new world is complex, but it's worth the investment to map it. To do this digital reconnaissance, it's crucial to measure business results on a per-creative, per-platform, per-audience basis," said Mark Rabkin, Facebook's VP of core ads in a blog post.

"An advertiser's ability to measure the right things properly will be the biggest predictor of their mobile advertising success," he added.

In effect, he suggested that advertisers should be less concerned about the two-second standard for an ad to be considered viewable, and instead adapt their ads for each new mobile format and then measure the results.

Autoplay video ads, for example, are viewed for an average 5.7 seconds in Facebook's news feed, while videos without ads are watched an average 16.7 seconds per view.

"Even though aggregate advert time is up, individual session times are down. People aren't watching adverts for as long as they used to, on any medium," Rabkin said, adding that no mobile platform can sustain "run of the mill", 30-second spots at the scale that TV once provided.

"Mobile has shown us that we no longer have the right to disrupt. Instead, we have to earn people’s attention," he said. "If marketers with fixed budgets are going to meaningfully connect with audiences and drive growth, they have to keep pace in this new, complex landscape and optimise for mobile content."

To achieve optimisation, Rabkin recommended that advertisers build new, short-form, mobile creative. "Ensure the video rewards people’s attention and tells its story, even if only the first few seconds are watched," he said.

In addition to measuring the results an ad achieves, rather than its length in seconds, advertisers should also test and measure ads on a weekly basis, he added.

Furthermore, each new mobile format – whether news feed or TrueView or other options – comes with different consumer expectations and behaviours.

That means advertisers should "be careful of false equivalences or standards between them that can blind your organisation to their unique nature".

"Facebook isn't YouTube, YouTube isn't Search, Search isn't Snapchat," Rabkin said.