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By Ari Levy, CNBC

Cord cutting just keeps getting easier.

Apple, Google and are adding over-the-top content to their streaming devices at a stepped-up pace, further challenging the traditional cable TV bundle.

Roku, which competes with those vendors in the market for streaming sticks and boxes, is going a step further, embedding its software into ultra-high definition televisions. Starting Thursday on Amazon's website, consumers can buy 4K televisions — TVs with resolution of around 4,000 pixels — co-branded by Roku and Chinese manufacturer TCL.

Read More from CNBC: U.S. Media Titans Tangled Up in Cord Cutting

Ranging from $499 for a 43-inch screen to $1,099 for a 65-inch display, the 4K TCL Roku TVs include all the functionality of a Roku box or stick, with the full TV user experience now in the hands of Roku. That means there's a simple remote with just a few buttons and voice controls that let the user search for a show or movie across thousands of channels.

Research firm Parks Associates estimates that 86 million streaming devices will be sold globally by 2019. Among U.S. households with broadband, Roku leads with 37 percent market share, followed by Google Cast (previously Chromecast) at 19 percent, Apple TV at 17 percent and Amazon Fire at 14 percent.

Nobody is sitting still.

Earlier this week, Apple announced upgrades to its set-top box, while Google said that its rebranded Cast service is being built into a line of Vizio smart TVs.

Netflix streaming is a key ingredient with all these devices, and the companies are increasingly eating into cable TV subscriptions by offering on-demand services from HBO, CBS, NBC, Hulu and ESPN.

Read More: Comcast Sells Cord-Cutting Service That Requires Comcast's Cord

"Today's content landscape is moving very quickly for OTT, and for streaming period," said Chas Smith, a Roku senior vice president. OTT, other-the-top, content is delivered over the Internet, typically on demand. "For 4K, it's evolving even faster."

To get the 4K experience, content has to be made specifically in the higher resolution. Roku is highlighting some of the available 4K shows and movies in a Spotlight channel on the device.

Roku partnered with TCL two years ago for an earlier generation of high-definition smart TVs. The companies announced at the Consumer Electronics Show in January that they've sold more than 1 million units.

It's a new business model for Roku, which is accustomed to making money from hardware. Now, TCL is selling the devices and Roku is left to generate revenue from the platform. That can happen by selling services and channels, similar to how consumers buy mobile apps, and through advertising as more content becomes streamed.

"The more engagement we can get with consumers, the more opportunities there are to monetize that experience," Smith said. "Once all TV is streamed, all advertising is streamed. If we're at the center of it, that's a great place to be."