The blowout quarters keep coming for Roku (NASDAQ:ROKU). The company behind the fast-growing video-streaming platform came through with another monster earnings report after Wednesday's market close, sending the shares up to all-time highs on Thursday.

Roku stock has now almost quadrupled in 2019, and one of this year's hottest investments could just be getting started. Let's go over some of the secrets to Roku's success, and how they can keep paying off in the future.

A Roku TV showing free streaming options.

Image source: Roku.

1. Engagement keeps growing

There are now 30.5 million active accounts on Roku, 39% more than it was serving a year earlier. A whopping 9.4 billion hours were streamed through Roku's gateway, a 72% surge over the past year. The average account is now streaming more than three hours a day, and if you think that's the ceiling -- because who has three hours and change to watch TV? -- keep in mind that we're talking about accounts and not individual users. Entire families can feast on a single Roku-propelled device.

Bears probably thought the metric reached its ceiling a year ago when the average was 2.7 hours a day, and now it's at 3.4 hours. More time spent with Roku increases the familiarity that will make it too sticky to replace, and it also means more money for Roku as it cashes in on ads it can serve up and collects referral royalties. Average revenue per account is up 27% over the past year, to an annual run rate of $21.06. 

2. Platform revenue is everything

The biggest transformation at Roku since it went public, two years ago, is that low-margin device sales no longer make up the majority of its revenue. High-margin platform revenue topped two-thirds of the revenue mix for the first time in the second quarter. 

Device sales are starting to wake up -- 24% higher in Wednesday's report, as opposed to flattish at the time it went public -- but it's the 86% pop in platform revenue that's really driving this train now. We've now seen revenue accelerate sharply for three consecutive quarters, rising from 38.9% to 59.5% in that deliciously rewarding span of time for shareholders. Platform revenue is the primary reason for the acceleration. 

3. Roku is in the right place at the right time

If you think there are a lot of streaming services now, just wait a few months. Most of the major media giants are rolling out flagship services between now and next year, and that's going to make Roku even better.

The media networks that have been feasting on chunky revenue from cable and satellite television providers see the writing on the wall. The migration to streaming is real, and with more money riding on getting noticed, it's a safe bet that Roku -- the leading operating system for smart televisions -- will be cashing in as old-school media giants pay up for eyeballs on the media of the future. For now, all roads lead to Roku.