Within the next five years, Google’s YouTube could generate $15 billion or more in annual revenue — which would make it about the same size as CBS or Viacom, a Wall Street analyst predicts.

“We think the odds are extremely high that YouTube will be a large, profitable and highly consequential business” in the next few years, Sanford Bernstein senior analyst Carlos Kirjner wrote in a research note Friday. “It is becoming an attractive and important medium for brand advertisers, and we think it will increasingly compete (with traditional media companies) for the incremental video-delivered brand advertising dollars.”

The vidsite now streams 6 billion hours of video to more than 1 billion unique users per month across the globe. In the U.S., YouTube now reaches a bigger audience of adults 18-34 than any single TV network, global head of content Robert Kyncl said at Google’s YouTube Brandcast event this week, citing Nielsen analysis.

Google does not break out results for YouTube in its financial statements. In 2012, the website was expected to haul in net revenue of $2.4 billion, according to an estimate last year by analyst Mark Mahaney, who previously was with Citigroup and joined RBC Capital Markets earlier this year.

YouTube is strategically crucial for Google to maintain growth, as core search revenue decelerates over the next few years, according to Kirjner.

This spring, YouTube is expected to launch a handful of subscription-based channels from premium content providers. That could represent another important revenue stream, in addition to YouTube’s ad sales. Site already offers pay-per-view streaming movies and TV shows from major studios and nets, though it’s not clear how significant that business is.

As far as ad-supported professionally produced content, YouTube appears to have shifted gears after fronting a $200 million investment in original channels starting in 2011. At Wednesday’s NewFronts event, Kyncl said YouTube has moved away from “these waves of announcements” on original channel partners. “Now it’s simply about finding the right talent and content,” he said.

Beyond YouTube, Google has embarked on initiatives including Google Fiber, self-driving cars and wearable Google Glass devices in an attempt to build new businesses that will fuel growth.

Google Fiber, which provides ultra-fast Internet and TV, is currently live in Kansas City metro area and the company has announced plans to bring fiber service to Austin, Texas, and Provo, Utah. On Thursday, the city council of Shawnee, Kan., a suburb of Kansas City, voted to approve a franchise for Google Fiber.

“We believe it is perfectly possible that Google achieve an attractive IRR (internal rate of return) for its Fiber deployment,” Kirjner wrote. “If that is the case, it could be passing several million U.S. homes in a few years and may be even expanding overseas.”

Kirjner previously expressed doubts that Google will be able to achieve favorable economic returns on a widespread fiber-to-the-home expansion. If Internet giant hits pay dirt with fiber, self-driving cars, Google Glass or other nascent projects, “those who call such initiatives ridiculous or a waste will feel very much like those who said the same of the YouTube acquisition not that long ago,” he wrote in the note Friday.

Sanford Bernstein analyst has an “outperform” rating on Google, with a target price of $1,000 per share (compared with $829.61 per share May 2 closing price).