AT&T has a rationale behind its recent acquisition spree.

The company wants to dominate the business of selling targeted advertising on internet-connected TVs and devices, according to advertising executives who have had conversations with the company.

On the content side, AT&T acquired Time Warner for a whopping $85.4 billion, though the Department of Justice is suing to block the deal. It purchased entertainment company Otter Media for a price reported around $1 billion. It's also buying advertising tech such as the digital ad platform AppNexus, which it reportedly got for around $1.6 billion. AT&T has met with additional advertising technology companies about potential acquisitions.

The endgame for AT&T is to develop a new ad platform to sell targeted advertising on video content, regardless of where the person is watching and whether they have a cable or satellite subscription.

For instance, ads could appear on television shows and movies owned by AT&T, even if those shows run on non-AT&T distribution platforms like Apple TV or Roku. Partners could also sign up to use the platform, letting AT&T sell advertising against content owned by other companies. This ad platform could take more than a year to develop, according to sources.

It's an ambitious play for AT&T, as people are increasingly getting their entertainment from mobile devices, online sources and through streaming. By the end of last year, about 22.2 million people aged 18 and up in the U.S. no longer had a satellite or cable subscription, according to eMarketer. Almost 60 percent of Americans have at least one streaming service, according to a CNBC survey.

"This audience is called the 'unreachables' because they are tougher to reach for brand awareness and brand campaigns," said Ashwin Navin, CEO of television data analytics company Samba TV. "The assets that AT&T is putting together through acquisitions could recover that audience, which is watching TV in a different way today."

It also gives AT&T a chance to grab more of the massive budget advertisers are still allocating toward TV, which amounts to about $70 billion a year in the U.S., according to eMarketer. AT&T's platform could become the main way for brands to buy ads on streaming premium television shows and movies, a marketplace Facebook hasn't entered and Google is just starting to explore.

"YouTube wouldn't reach the cord cutters specifically, and Google and Facebook's audiences are much too narrow for what linear [scheduled] TV used to reach," Navin explained.

When contacted about its plan, AT&T pointed to its AppNexus acquisition announcement in June where it said it hoped to "strengthen its leadership in advanced TV advertising," but declined to comment further. "Advanced TV" is an industry term for streaming TV content, including programming watched on internet-connected TVs, digital media devices and mobile phones. It also includes cable/satellite and video-on-demand programming that can handle highly-targeted ads.