Comcast (NASDAQ:CMCSA) revealed a lot of details about its forthcoming streaming service, Peacock, earlier this month. It'll be mainly ad-supported. It'll have lots of live and on-demand content. And Comcast cable and internet subscribers will get early access to everything Peacock has to offer.

But there's still one big question: Will Peacock be able to partner with other companies for distribution?

At the event unveiling Peacock, management talked about partnering with other pay-TV providers for distribution. It also showed off the streaming service on its X1 platform, which is licensed by Comcast's first distribution partner, Cox Communications. Comcast internet subscribers will be able to stream the service on Comcast's own Xfinity Flex platform.

But most consumers use one of two platforms to stream video on their televisions: Roku (NASDAQ:ROKU) or Amazon's (NASDAQ:AMZN) Fire TV. Comcast could have trouble negotiating deals with the connected TV leaders, which could seriously harm its growth prospects.

Peacock homescreen on a TV powered by Xfinity Flex, surrounded by a laptop, tablet, and smartphone displaying the Peacock logo.

These are the devices that support Peacock. Notice what's missing. Image source: Peacock.

The connected-TV duopoly Comcast is dealing with

Roku and Amazon combine to account for nearly 70% of all streaming devices in the United States, according to data from Parks Associates. Not only that, but both companies are seeing their installed bases grow faster than the rest of the industry. In other words, they're growing their market share.

That has serious implications for a company like Comcast that's trying to get its streaming service into the homes of 35 million viewers over the next five years. Roku and Amazon can be hard-nosed negotiators.

Disney (NYSE:DIS) notably saw negotiations with Amazon stretch out to the final week before Disney+'s launch. The two were stuck negotiating ad-inventory shares on Disney's other apps. Considering Comcast expects most Peacock viewers to use an ad-supported version of the service, it could face a similar challenge from Amazon or Roku.

Peacock's ad load plans could make a deal even tougher to reach

One thing Comcast's management continuously harped on during its presentation was the industry-low ad load in Peacock. The service will show a maximum of five minutes of ads per hour, which is nearly half of Hulu's ad load.

Amazon and Roku make money by taking a share of ad inventory in most ad-supported apps. Some very popular apps that make the platform more attractive, like Alphabet's YouTube, often get a pass or share very little inventory, but new upstarts like Peacock generally have to share more -- typically around 30% of inventory.

Since advertising -- and the ad experience -- are an important part of Peacock, Comcast, Roku, and Amazon may have an even tougher time coming to terms they can agree upon.

Can Comcast go without a distribution partner?

Comcast is a distribution company in its own right. Practically all of its 20 million cable TV subscribers receive video through its platform. Additionally, its broadband subscribers, of which it has around 26 million, are all eligible to receive its Xfinity Flex set-top box at no additional cost. Comcast is also looking to partner with other pay-TV distributors to include Peacock in their set-top boxes.

Peacock's pricing and Comcast's efforts to partner with other pay-TV distributors is indicative of the company's strategy to make Peacock more of a complement to pay-TV than a competitive offering in the streaming space. And its modest goal of just 30 million to 35 million viewers within five years of launching also suggests it's not as aggressive about scaling its service as consumer discretionary competitors like Disney.

But there will surely be consumers without a Comcast subscription that are at least mildly interested in Peacock. Comcast will offer Peacock to everyone, albeit at a slightly higher price than if you have a relationship with Comcast or one of its partners. How will those people stream Peacock if there's no support for Roku or Amazon?

If Comcast wants to see engagement at any meaningful level, it needs to go to the places where consumers are streaming video. But supporting Roku and Amazon's platforms could detract from Comcast's main goal of supporting the cable TV ecosystem that represents the core of its business. Additionally, those partnerships will eat into the advertising inventory that'll be Peacock's main source of revenue. Comcast's unwillingness to go all-in on streaming video the way Disney has puts it in a tough position.