Rhythm NewMedia saw huge growth in mobile video advertising in the first quarter: 36 percent more than the fourth quarter of last year.

Part of that growth may have been driven by the addition of more publishers and advertisers using its network, but Director of Marketing Lisa Abramson says the whole addressable mobile video market has grown.

The first-quarter data includes ad campaigns from more than 70 Fortune 500 brands; Rhythm served more than 728 million average monthly content views in the quarter in the United States. Its brands include P&G, GM, HBO, Kraft and Disney, and publishers include CBS, ABC, NBC Universal, Fox, Warner Bros. and more.

Rhythm finds that in-stream video ads, which automatically play as a commercial break during full episodes or in-stream before video clips, outperform all other video units, with a high average completion rate of 87 percent. Interactive pre-roll ads, which are seen before an app launches or between a screen change, averaged 27 percent completion rate, and tap to interactive video (which involves taps from a display ad) had a completion rate of 21 percent.

As for who’s viewing mobile video advertising, Rhythm says 40 percent are watching videos, 50 percent are playing games and 80 percent are viewing articles or photos.

Rhythm recommends combining ad units for maximum effectiveness and says it’s the only mobile advertising solution to provide all three types of video experiences: in-stream video, interactive pre-roll and tap to interactive video.  

Data points in Rhythm’s quarterly report are based on ads served across iPhone, iPod Touch, iPad, Android and other devices in the U.S. market, including tablets. Brands in the categories of entertainment, telecom and consumer packaged goods ran the most campaigns during the quarter.

So, will traffic spike later this week when the big event takes place in London? Abramson says she’s not aware of any Rhythm advertisers planning a specific mobile campaign around the royal wedding, but Rhythm works with plenty of entertainment news sites, so it’s likely there will be more traffic as people tune in for video highlights.