Shares of Roku (NASDAQ:ROKU) hit a fresh, new all-time high Tuesday, topping off already impressive gains in 2019. The streaming pioneer has crushed the market so far this year, up an incredible 271% thus far.

So what is it that is sending shares of Roku stock through the roof? Two completely unrelated catalysts fueled the stock's run today, but it's the underlying strength of its business that has driven the train thus far this year.

Here are the two recent items that drove Roku to fresh heights.

A TV displaying The Roku Channel with the caption Premium Subscriptions on The Roku Channel.

Image source: Roku.

An analyst upgrade

Roku got a little love from boutique equity research firm CrispIdea, which upgraded Roku stock to buy from hold. The company cited a number of reasons for its bullish stance, including Roku's impressive revenue growth. 

There's no doubt that Roku's revenue has been soaring in recent months. The company capped off 2018 with heady 45% year-over-year revenue growth for the full year. Even more impressive, however, is Roku's platform segment, including its advertising revenue, which grew by 85% compared with 2017. 

Roku continued its high-flying performance coming into 2019, with revenue that accelerated to 51% year over year in the first quarter, while platform revenue turned in impressive 79% growth.

One of the key drivers to its revenue growth is the continuing expansion of its user base. Roku's active accounts grew to 27 million in the fourth quarter, up 40% year over year. That continued into 2019, jumping to more than 29 million, also up 40% compared with the prior-year quarter. Engagement among those users has been soaring, with streaming hours in the first quarter topping 8.9 billion, up 74% year over year.

A Prime shopping day's Prime Day shopping event is currently winding down, and there are indications that Roku devices were strong sellers during the event.

Roku designed an operating system (OS) tailor-made for smart TVs and has been licensing it to a host of device manufacturers. The business is booming for Roku, with one in three smart TVs sold in the U.S during the first quarter equipped with Roku technology -- making the Roku OS the No. 1 selling smart TV OS in the country. While the company makes very little on the licensing deals themselves, it puts Roku's streaming platform in front of a growing audience of viewers and helps supercharge the company's advertising business.

Amazon reported that Roku-equipped TVs and streaming devices were among the best-selling electronics during Amazon's two-day sale. The third-best-selling television during the event was the 32-inch Roku-enabled TCL TV, which sold for $99, according to Amazon. 

"The market thinks [Roku's] a beneficiary of Prime Day," said Wedbush Securities analyst Michael Pachter. "The more televisions sold with Roku operating systems, the greater their opportunity to sell ads, or subscriptions to content providers like Netflix," he said. 

Roku gets a cut every time a subscription to a streaming service like Netflix or HBO is generated on its platform.

There's more growth to come

While it is Roku's unbelievably strong execution that has fueled the majority of its gains, little wins -- like an analyst upgrade, or being among the best-selling products during Prime Day -- provide evidence that the growth story remains intact. And it could be just the beginning. If Roku's underlying business continues to grow like wildfire, the sky's the limit.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.