Vertical videos, long considered a vexing eyesore when uploaded to YouTube amid two gaping black bars -- and which even spawned a popular meme known as Vertical Video Syndrome -- are suddenly looking like the favored orientation du jour for video platforms, marketers and media companies alike.

The about-face began earlier this summer when Snapchat unveiled its highly-anticipated ad strategy. Rather than jamming horizontal television ads into a digital interface, as had been the norm, the mobile-born platform made vertical video a key touchstone of its pitch to marketers. Vertical ads completely fill mobile screens, the company argued, and don’t require users to constantly flip their phones.

While asking brands to shoot or recut ads vertically may have been a jarring -- and costly -- proposition, Snapchat says the payoff is irrefutable. Vertical video ads are nine times more likely to be viewed to completion than their horizontal counterparts, according to the company.

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Snapchat isn’t alone in this view. Other video platforms that are nascent to mobile, including Periscope and Meerkat, emphasize a portrait orientation (though Meerkat does offer a landscape option.)

Full-screen vertical videos are also now viewable on Facebook, which last month announced forthcoming vertical ads touting touch-navigated, 360-degree viewership.

And finally, the world’s biggest video behemoth has hopped on the vertical bandwagon as well. YouTube may have risen to prominence on desktops 10 years ago, but now half of all views take place on mobile devices. Accordingly, the company unveiled a redesigned app last month that will accommodate vertical videos -- meaning those unseemly black bars will soon be gone for good.

Related: YouTube CEO Unveils Redesigned App, Additional Creator Spaces

Given this noteworthy shift, leading media companies are reimagining their approach to content creation. The Daily Mail, which is one of Snapchat’s 11 exclusive media partners, is “aggressively” developing both vertical creative and ad content, wrote CEO Jon Steinberg in a blog post.

Furthermore, Mashable published its first story yesterday -- an interview with Cronut inventor Dominique Ansel -- featuring a video that will appear vertically on both mobile devices and PCs.

“With our new vertical video player, we're bringing video to our community in an aspect ratio that's native and natural for mobile," said Mashable’s vice president of product management, Darren Tome.

Marketers, take note: as audiences consume more and more videos on their smartphones, you must be willing to drastically alter your perspective in order to fully engage.

Related: Twitter's Head of Video Hints at Monetization Plans for 'All' Creators