The average amount of time a day people spend watching online video will increase by 23% in 2015 and a further 19% in 2016, driven by the rapid rise in the adoption of smartphones and tablets. Mobile devices are expected to become the main way of viewing online video in 2016. Meanwhile the number of people regularly watching traditional television will peak this year and will then start to decline for the first time. That is the forecast of ZenithOptimedia, part of the Publicis Groupe.

The Online Video Forecasts report predicts that video usage on mobile devices will grow by over 43% in 2015 and over 34% in 2016. ZenithOptimedia expects mobile to become the main platform for viewing online video, accounting for over 52% of online viewing in 2016 and 58% in 2017.

Furthermore, the firm predicts that the number of people regularly watching traditional linear television will rise by 3.1% to peak in 2015 and start to decline for the first time, shrinking by 1.9% in 2016 and 0.9% in 2017. In other words about the same number of people will be watching television in two years.

ZenithOptimedia says the number of regular linear TV viewers has been in decline in France and Russia since 2013, in the United Kingdom and the United States since 2014, and is expected to start to decline in China this year. It says the decline of linear television viewing is in direct correlation with the increasing quantity and quality of content available online, both from short-form platforms like YouTube and long-form platforms like Netflix.

It expects the number of regular online video viewers will increase by over 5% in each of the next three years, with double digit grown in some markets.

Online video is the fastest-growing category of online advertising. It is forecast to account for an eighth of global internet advertising spending in 2017, when it will be worth $23.7 billion, with the United States still accounting for around half of that.

Nevertheless, the vast majority of viewing is still on the traditional television set. Television advertising is still a £100 billion market worldwide.

Online Video Forecasts is published by ZenithOptimedia and is based on an analysis and forecast of online video usage and advertising expenditure in 40 countries around the world.