The growth of video has been well documented. People spend more time watching video than they do on social media, and Cisco projects that 80 percent of all Internet traffic will be video by 2019.

Video usage on smartphones and tablets is growing even more quickly. Mobile video consumption is expected to surpass desktop consumption by the fourth quarter of 2016.

But while it’s clear that mobile video is growing at an incredible rate, it’s less clear how consumers are viewing video on mobile devices, especially smartphones. Which way do they hold their phones? Do they watch only short videos and leave longer ones for larger screens? And where are they watching?

Here are the answers to those questions.

Horizontal or vertical?

Once the mark of an amateur videographer, vertical video is making a comeback thanks to smartphones. When widescreen desktop monitors reigned, vertical videos were an unnatural fit, leaving wide black stripes on either side of the screen.

Now people spend 29 percent of their time looking at smartphones with vertical screens, up from five percent five years ago. Suddenly it’s horizontal videos that are an inconvenience, forcing viewers to turn their phones sideways to see content comfortably.

Leading digital publishers like National Geographic, Mashable and Vox have responded by creating vertical videos (with smartphones or cameras rotated 90 degrees) or by framing horizontal videos in such a way that they can be easily cropped to fit vertical screens. When they’re viewed on horizontal screens, these videos are moved into a sidebar or placed alongside a large quote to optimize landscape real estate.

Advertisers using vertical video have found success. On Snapchat, a social network designed for vertical usage, vertical video ads show completion rates up to nine times higher than horizontal ads.

Short or long?

It may come as a surprise, but people don’t only watch short videos on their smartphones. According to a global Interactive Advertising Bureau study, 36 percent of smartphone users watch videos five minutes in length or longer on a daily basis.

While 36 percent is a smaller number than the 58 percent who say they watch shorter videos daily, that number is likely to grow as phone manufacturers continue to produce devices with bigger and better screens.

Instagram, owned by Facebook, recognized this trend when it increased video length from 15 seconds to 60 seconds for all users in March 2016.

YouTube or social media?

Less surprising is that YouTube is king when it comes to mobile video. Among respondents to the IAB survey, 62 percent said that YouTube is where they find the videos they watch on their smartphones. More than half of YouTube’s billions of daily views are on mobile devices.

Even with the explosive growth of video on Facebook, Instagram and Snapchat, social media lags well behind YouTube, with 42 percent of IAB survey respondents naming it as the source of the videos they watch. So while social media is a great way to spread your video content, odds are you’re missing viewers if you’re not posting them to YouTube as well.

What about virtual reality?

Virtual reality isn’t only a product of science fiction anymore. Since Google released Google Cardboard, its virtual reality viewer for smartphones, it’s shipped more than 5 million units, and many more users have downloaded instructions for making their own viewers. Google Cardboard users have watched more than 350,000 hours of virtual reality videos on YouTube.

The Royal London Hospital was the first hospital in the world to publicly use the technology, streaming a colon cancer procedure performed by Dr. Shafi Ahmed for anyone with a virtual reality headset. More than 54,000 people viewed the broadcast worldwide. With virtual reality, patients may soon be able to understand complicated treatments and procedures better than ever before.