Netflix is the heaviest hitter in the movie-streaming universe, with Hulu providing major competition. And now, the biggest presence on the Internet has just crashed the party.

Social networking behemoth Facebook has teamed with Warner Brothers., a division of Time Warner, to offer movies on the Facebook site. Customers can rent the films for 30 Facebook credits, about $3. The movies will be available for 48 hours. Viewers can pause or restart a movie if they leave the site and log back in.

Only one movie is available on the Warner Bros. Facebook page, the 2008 Batman flick The Dark Knight. However, expect that to change in the upcoming months, if not weeks.

Dark Knight was chosen because it has already been "liked" by almost 4 million users. Want to see this movie on Netflix's on-demand Web service? Too bad -- it doesn't have it.

The Facebook service will initially be available only in the United States, but with 600 million users all over the globe, that should change down the line as well. Overseas Facebook fans would provide a serious revenue stream for this project.Facebook's cut of income generated from the streamed films is said to be 30 percent.

"Making our films available through Facebook is a natural extension of our digital distribution efforts," said Thomas Gewecke, president of digital distribution at Warner Bros. "It gives consumers a simple, convenient way to access and enjoy our films through the world's largest social network."

Warner Bros' decision to partner with Facebook comes at a time when DVD sales are plunging. The media-tracking firm HIS Screen Digest says that U.S. sales of DVDs checked in at $7.8 billion, down 43 percent from its high in 2006. Sales went down 20 percent from 2009 to 2010.

As people move away from purchasing or renting DVDs, viewing movies streamed online is becoming increasingly popular. Netflix said earlier this year that it had 20 million subscribers, a 63 percent hike from a year ago. Some six percent of the country's population are Netflix subscribers, a lot of them signed up for its lucrative streaming operation.

"Netflix members are already watching more TV episodes and movies streamed instantly over the Internet than on DVDs," a Netflix executive said recently. "And we expect that trend to continue."

Besides Facebook, $1 DVD rental kiosk service Redbox is also planning to jump into the online video streaming service scene. It will be subscription based rather than pay as you go, as is the case with DVD rentals.

Coinstar, Inc., which owns Redbox, is planning to launch its streaming service with a partner, which has yet to be revealed. There are rumors that it could be Amazon.

Nevertheless, that Facebook is steaming into streaming certainly shook up investors. In Nasdaq trading, Netflix shares tumbled 5.8 percent after the announcement, while Coinstar shares dropped 5.3 percent.

"Facebook is a force to be reckoned with," said Youssef Squali, an analyst with Jefferies & Co, to Bloomberg.com. "We expect the test will pick up steam as more titles become available... we expect more film studios to sign on as well."

Goldman Sachs analyst Ingrid Chung believes that Netflix will stay on its perch as the video service provider -- at least for now.

"We believe that on a short-term basis, this isn't an immediate threat to Netflix," Chung told the Wall Street journal. "On a longer term basis, we think that Facebook could become a credible threat as its video business evolves."

In other words, gear up for a heavyweight fight in movie streaming.