Global viewing of over-the-top video content more than doubled last year to 12.6 billion hours, according to a new report by Conviva.

Viewing was done on more than 2.4 billion devices, up 9%, Conviva said. The U.S. accounted for 58% of OTT viewing, followed by Europe with 21%, Asia with 19% and the rest of the world with 2%.

“Conviva has seen the viewing hour growth rate accelerate over the past several years as more consumers move their TV-watching from traditional linear pay TV services to a very wide variety of OTT services offered by both pure play OTT publishers and MVPDs, as well as pay TV providers diversifying their service offerings,” the company said in its Streaming Market Year in Review report. “Conviva expects to see continued accelerated growth over the course of 2018 across both existing and new customers.”

The data in the report is based on Conviva customers, which the company said cover close to 60% of the internet population. The company measures seven out of the top 10 SVOD providers in the U.S., as well as other OTT providers globally.

The number of views initiated in 2017 rose 74% to 38.8 billion, with 54% of those in the U.S.

By December, 64% of traffic on Conviva’s platform came through video apps, compared with 36% from watching video through browsers. That’s the opposite of the year prior. Video app activity grew 160%, while browser video rose 23%.

As many as 1.04 billion unique streaming apps reside on devices in the U.S., with 2.2 apps per device and 2.9 devices per person.

Conviva said the peak in concurrent video connections was 9.75 million, with spikes for both live sports and original content.

In-home devices, such as the Xbox and Roku platforms, showed the highest completion rate for video programming at 46%, with 71% growth in viewing time per device, Conviva said. Streaming video programming was more likely to be interrupted when viewed on a mobile device.

In terms of quality of OTT video, Conviva said that of the 47.1 billion attempts to start watching a video, 38.8 billion were successful. It took an average of 4.84 seconds for a video to start, a 23% improvement from the previous year.

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Buffering issues improved slightly. While watching a half-hour show, the average viewer spent 0.95% of the time, or less than 18 seconds, waiting for video to rebuffer.

“The OTT market continues to see explosive growth not only in the number of viewers, but the amount of time spent viewing as well,” Conviva said.