• by Erik Sass , Staff Writer @eriksass1, June 5, 2015

Americans are watching more and more mobile video, but ad dollars aren’t migrating to the new medium as quickly as might be expected, according to a new report from eMarketer. Mobile video advertising is currently hobbled by a number of problems, including technical issues and challenges in the marketplace, which need to be resolved before advertisers feel confident allocating more video ad dollars.

Total spending on mobile video ads in 2014 came to $1.54 billion, according to eMarketer, compared to $4.27 billion for desktop video ads. This year eMarketer expects those figures to increase to $2.62 billion for mobile and $5.15 billion for desktop. In proportional terms, that means mobile’s share will edge up from 26.5% of all digital video ad dollars in 2014 to 33.7% in 2015.

Looking ahead, eMarketer sees mobile video ad spending increasing to $6.86 billion by 2019, compared to $7.52 billion for desktop, giving mobile almost half (47.7%) of all digital video ad spending.

While these figures are impressive, eMarketer points out that they are actually low when compared to mobile’s share of digital advertising overall. Looking at all types of digital advertising, mobile’s share is projected to reach 72.2% of total spending by 2019, leaving desktop with a little over a quarter.

Mobile’s ad spend also lags behind viewing times: in 2015, mobile will account for an average 39 minutes of viewing time spent with digital video, out of a total 76 minutes. That works out to 51% of viewing minutes, compared to just a third of ad dollars.

So why can’t mobile video ad spend keep pace with viewing time and other types of mobile ads? The report attributes its relatively slow growth rate to the confusing variety of ad formats, uneven quality in ad inventory, and lack of consensus on metrics and pricing. Advertisers are also unsure whether, or when, to use mobile Web or in-app ads.