The growth of Snapchat’s mobile video traffic is staggering.

Snapchat users view, in aggregate, more than 7 billion videos through the ephemeral photo and video sharing app per day, a source close to the matter confirmed with Fortune. Between June and Nov. last year, Snapchat’s video traffic more than tripled to 6 billion per day, according to an earlier Financial Times report.

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Most of these gains can be attributed to Snapchat’s “stories” feature, notes Bloomberg, which first reported the latest figure. Stories allows Snapchat users to broadcast concatenated video clips and photos to their contacts for 24-hour periods.

The 5-year-old company is valued at $16 billion, placing it at no. 5 on Fortune’s “unicorn” list of startups valued at $1 billion dollars or more. Investors base much of this perceived value on potential revenue to be generated from digital advertising. As the service attracts more eyeballs, it becomes a more attractive destination for ad dollars.

Read: “How Facebook’s video-traffic explosion is shaking up the advertising world”

In comparison, Facebook fb last reported that its users watched 8 billion videos per day on both desktop and mobile at the end of the company’s third quarter. The social network boasted 1.55 billion monthly active users at last count, however. That’s 15 times as many as Snapchat, which Evan Spiegel, the company’s co-founder and CEO, last said had 100 million daily users.

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Google-owned goog YouTube, the previously uncontested industry leader, does not break out how many daily video views it receives. “Every day people watch hundreds of millions of hours on YouTube and generate billions of views,” the company reports on its website.

Controversially, Facebook tallies any auto-play video that runs for at least three seconds in a person’s news feed as a “view.” Some critics have considered this seemingly arbitrary cut-off too short a timespan to gauge whether a viewer is actually paying attention to a video.

A person familiar with Snapchat’s metrics told Fortune that the company counts a view only after a user has engaged or opened a story or message—meaning once the video renders, rather than when it is loaded.