The study, by mobile ad platform Opera Mediaworks, analysed campaigns from ten brands in the EMEA region, including eBay, Mitsubishi, Stella Artois and TomTom, comparing engagement and dwell times. 

It emerged that while there were on average 36% higher engagement levels for shorter campaigns, a six-second ad by Stella Artois delivered 60% higher engagement compared with a 15-second version. 

Short form video also resulted in 25% longer dwell times, leading the report to conclude that short-form video is likely most effective for branding campaigns. 

However, if a product-focused campaign had a call-to-action, it was found that ads lasting between 15 and 30 seconds delivered 30% higher engagement rates than shorter form content. 

"It has long been suspected that the length of mobile video creative has a direct impact on audience engagement rates, and it’s reassuring to have a specific measure of this now," said Mark Slade, managing director for EMEA at Opera Mediaworks.

"Mobile video continues to be a huge growth area for advertising, considering the ubiquity of smartphones and the changing habits of how we consume content."