The Publicis Groupe-owned media agency's Online Video Forecasts report found that the market will expand by a further 19.8% in 2016.
ZenithOptimedia also claims the number of linear TV viewers will begin to decline in 2016 for the first time, after a peak this year. It said the number will rise to 3.1% in 2015, then drop by 1.9%, and then 0.9% in 2017.
The number of people watching videos on mobile devices is expected to grow by 43.9% in 2015 and 34.8% in 2016.
On non-mobile devices the research said that video consumption will rise by 9.5% this year and by 6.5% in 2016.
In terms of time spent on mobile, ZenithOptimedia said that it is becoming the main platform for viewing online video.
In 2012 the devices accounted for 22.9% of time spent watching online video, globally. In 2014, this increased to 40.1%. ZenithOptimedia expects viewing time to reach 52.7 next year, and 58.1% in 2016.
It means that global online video adspend is also rising "rapidly." The market had an 8.8% share of the total internet adspend in 2012. Last year this rose to 10.2% and it is predicted to increase by 12.8%.
Online video is also the fastest growing sector in internet advertising. The report forecast it to grow by 28.9 per cent to $16.1 billion globally in 2015, 22.5% in 2016 and 19.7% in 2017 to $23.7 billion.
According to Mark Waugh, the global managing director at Newcast, the branded content arm at ZenithOptimedia, "Consumers all around the world are rapidly embracing online video, because it offers them a near limitless array of engrossing content.
"Some of the keenest users are the young, affluent viewers who are hardest to reach on television.
"Brands are finding online video a particularly effective way to reach these valuable audiences, not just with advertising, but also with branded content; content that can inform or entertain consumers in a deeper and richer way than is possible with short, interruptive ads."
This article first appeared on campaignlive.co.uk.