LAGUNA BEACH, Calif.—The war for tech supremacy is moving to newer technologies such as augmented reality and voice assistants, as giant internet companies grasp for an ever-fleeting portion of people’s time.

That is the tech and media outlook presented Tuesday at The Wall Street Journal’s WSJ D.Live technology conference by Michael J. Wolf, co-founder and managing director of the consulting firm Activate Inc. (Scroll down to see a slideshow of the presentation, or to the bottom of the article to view all the slides individually.)

Activate co-founder Michael Wolf breaks down the major forces that will reshape online shopping, virtual and augmented reality, and media consumption in the year ahead. He spoke at WSJ’s D.Live technology conference. Photo: Nikki Ritcher

Alphabet Inc., Facebook Inc., Amazon.com Inc., Apple Inc. and others are hunting for new areas of growth—often on each other’s turf—as they enjoy soaring revenues and stock prices. They are poised to bump into each other across the board, in online sports viewing, movies, news and even podcasting.

Up for grabs is an extra $300 billion a year in revenues that Activate projects will flow into the $1.7 trillion global consumer media and internet market by 2021, through growing internet-access fees, ads and paid content. Activate estimates the market will grow 4.1% a year.

Consumers’ time, though, is already stretched, with young people in particular tethered to devices much of the day. Mr. Wolf’s outlook estimates people spend 12 hours a day on average consuming tech and media, including moments when they are multitasking.

“Everybody’s trying to get into everybody else’s space because what they’re really fighting for is somebody’ else’s time,” said Mr. Wolf, a former Yahoo Inc. board member, in an interview before his presentation.

The most fertile ground is the digital voice assistant found in smart speakers and smartphones.

Between Amazon’s Alexa, Alphabet’s Google Assistant and Apple’s Siri, the internet giants are rushing to make more advanced products that could prove crucial to controlling consumers’ searches, their homes and habits, and even how they buy products. Sales of smart speakers, though, will likely peak in 2019, Mr. Wolf said, as the voice interface breaks free of the devices.

“The real war is about who gets to win the digital assistant and the voice interface,” Mr. Wolf said. “It’s an existential threat to each of the major technology companies.”

Along with opportunities to shape the future of voice-enabled devices, there are potential clashes as tech giants invade each other’s turf. Many questions asked of Alexa, for instance, require general web searches—Google’s expertise—while people who own a Google Home might shop for everyday goods, a task in which they otherwise might have turned to Amazon.

In shopping, Activate suggested consumers will move even further toward generic or private-label goods and foods as online retailers push their own products more.

WSJ D.LIVE CONFERENCE

Other growing markets include podcasts, an older technology enjoying a resurgence. Activate estimates the U.S. podcast audience will nearly double to 112 million active monthly listeners in 2021. Revenues, though, are still tiny in the young industry, expected to rise to $642 million from $237 million this year.

A similar nascent fight is shaping up in virtual and augmented reality, where Microsoft Corp., Google and Facebook have already dived in—and others are watching.

Despite years of high expectations, virtual reality will still be slow growing, Activate projects. Augmented reality, including glasses that display digital images over a person’s view of the real world, has big potential with sales to businesses, however. Activate estimates the AR and VR markets combined will grow to $71 billion in sales by 2021, up from $6 billion this year, with 66% made up by augmented reality sales to businesses.

In the news business, Mr. Wolf said he expects trusted brands to take on an increasingly dominant role amid concerns of fake news and dimming revenue prospects for small and local publications.

Cable television is also likely to remain the dominant form of TV-watching, as Activate estimates only 21% of U.S. households have enough internet bandwidth to support more than one device streaming shows over the internet.

Other findings from Mr. Wolf’s presentation:

• Sports-broadcast rights revenues are poised to grow by $3.5 billion a year by 2021, giving an opening to tech giants like Amazon, Facebook and Twitter, which have experimented with streaming online.

• Younger fans will drive viewership to emerging sports leagues such as Major League Soccer and esports. In esports, 62% of viewers are ages 18 to 34.

• Revenue from online videos—including subscription streaming services, individual purchases and online ads—are expected to make up about 15% of the $200 billion U.S. market for television and video in 2018.

• By 2021, Americans are projected to spend an additional 18 minutes a day with tech and media.

• Super users are more important than ever. The top 25% of video users capture 61% of the time spent. In gaming, the top 25% of players generate 70% of the play time.

Scroll to view all of the slides from Michael Wolf’s presentation at WSJ D.Live 2017.

Write to Eliot Brown at eliot.brown@wsj.com