Roku’s first-quarter revenue beat Wall Street estimates as COVID-19 quarantines have resulted in a massive streaming surge for the company. However, it warned that advertising revenue will see slower growth in 2020 than expected because of a pullback in U.S. spending.

The company said it ended Q1 with 39.8 million active accounts, a net increase of about 2.9 million from the prior quarter (when it added a record 4.6 million accounts) and up 37% year over year. Streaming hours in Q1 totaled 13.2 billion, a 49% year-over-year increase — a smaller year-to-year increase than the 68% jump Roku reported in Q4 and a sequential decline from 16.3 billion hours for the last three months of 2019.

Roku posted revenue $320.8 million — up 55% year over year, and higher than analyst consensus estimates of $306.7 million — and a net loss of $54.6 million (45 cents per share), in line with expectations. Shares of Roku were down over 9% in after-hours trading, as investors reacted to the company’s expectation that the pace of ad revenue growth would be impacted through the rest of the year. The stock closed up 7.8% in the regular session.

According to the company, the acceleration of growth in new Roku accounts and viewership continued in April. Active accounts grew roughly 38% last month versus April 2019, driven by a year-over-year increase in new accounts of more than 70%.

And in April, streaming hours rose by roughly 80% year-over-year, driven by an increase in streaming hours per account of about 30%. “The pandemic associated stay-at-home orders and increased unemployment appear to have accelerated the shift from linear TV viewing to streaming during the past few weeks,” founder/CEO Anthony Wood and CFO Steve Louden wrote in a letter to shareholders.

Since the crisis hit the U.S. in mid-March, Roku’s platform monetization has been a mixed bag. Subscription video-on-demand trials and subscriptions and transactional VOD purchases are up. But its advertising business has seen higher-than-normal cancellations as overall ad budgets have declined; that has been partially offset by spend that has moved from traditional TV budgets to Roku’s over-the-top video. The Roku execs said they expect the ad business will deliver “substantial revenue growth” on a year-over-year basis, “albeit at a slower pace and lower gross profit than we originally expected for the year.”

The COVID-19 pandemic is “obviously a massive health and economic crisis,” Louden said in an interview with Variety. “Some of the trends are positive for us, some of them are short-term negative. But most of these trends accelerate the long-term trend toward streaming.”

He added, “The positive for us in OTT is that for the money that’s left in marketers’ budgets, they’ll be looking for measurable and targeted spend.”

While Roku says it benefited from the boom in quarantine streaming, it rolled out a “Are you still watching?” feature in Q1 — which exits video playback after long periods of user inactivity, so was expected to reduce overall streaming time across its user base.

For the first quarter, sales in Roku’s Platform segment (advertising and subscription/transactional revenue) popped 73%, to $232.6 million. The Player segment (hardware) revenue rose 22%, to $88.2 million.

The company had already pre-announced that Q1 revenue would be slightly higher than previously expected, with other metrics generally in-line with prior outlook, while it pulled guidance for 2020 given economic uncertainty with the COVID-19 pandemic.

Earlier this week, Roku announced the OneView Ad Platform, integrating Roku’s advertising inventory with identity and attribution tools of demand-side platform Dataxu, which the company acquired in November 2019.