The US digital video advertising market is on pace to nearly double by 2019. This growth will be led by an ongoing shift toward mobile viewing, a host of digital platforms that now prioritize video and a growing assortment of content against which to advertise, as explored in a new eMarketer report, “The Essentials of Digital Video Advertising: Seven Best Practices for More Effective US Campaigns.”

Advertisers are guilty of the most obvious video errors, but publishers and platform providers sometimes share the blame. Among the more egregious offenses are serving the same video pre-roll multiple times during a content series, forcing long-form ads ahead of short-form videos, reusing video spots without regard to screen aspect ratios, and autoplaying—with audio!—without the user’s permission.

Almost any advertiser worth their salt knows that these lackluster experiences won’t deliver the desired results. And yet bad user experience is, if not the rule, certainly more than mere exception.

Given the massive shift toward smartphone and tablet video, focusing on the user experience means, by necessity, putting a premium on mobile. In 2015, for the first time ever, average daily time spent watching digital video on mobile devices in the US surpassed desktop time, according to data from comScore Inc., Nielsen and ZenithOptimedia. By 2017, mobile time will be almost double its desktop counterpart.

Since advertising follows viewership, it’s no surprise that video is one of the fastest growing areas of US mobile ad spending. Mobile video ad spending in the US jumped 80.6% in 2015 and is forecast to see double-digit growth through 2019, according to eMarketer. Those growth rates exceed search and other subsets of the display category, such as banners, rich media and sponsorships. It should be noted, however, that one of the nonvideo display categories is "other," which includes Facebook News Feed ads and Twitter Promoted Tweets, which are increasingly video oriented. However, even with this caveat, it’s clear that mobile video advertising is headed for steep growth and destined to become an increasingly important part of the mix for marketers and agencies.

As important as mobile is, putting too much emphasis on that channel can leave holes in a marketer’s digital video ad strategy. Desktop is still important, as are emerging platforms like connected TV. What works on one of these screens doesn’t necessarily work on another, so marketers that design for one screen at the expense of another are missing an opportunity.

Although this seems obvious—surely everyone knows that users are consuming content on whatever device is at hand—you wouldn’t know it from the video advertising on those devices. Many marketers and agencies have made inroads toward a true multiscreen mentality, but in the words of one expert, “we’re not quite there yet.”