Greystripe is best known for converting ads from Flash to HTML 5 for display in native apps across its advertising network. The service was wildly popular because it allowed ads to engage consumers with animation, touch interactivity and click-through actions on Apple's Flash-free devices, which were dominating the mobile market.

The mobile market is fragmenting, however, sending more users to the Android, BlackBerry and possibly Windows 7 platforms. Advertisers are increasingly interested in mobile websites as opposed to native apps, Greystripe says.

That's why as of today, Greystripe is expanding its ad network and its Flash-to-HTML 5 conversions to include display ads meant for mobile websites.

A mobile Web display ad built in Flash and converted to HTML 5 by Greystripe.

Advertisers are drawn to the mobile Web because there are fewer native apps to advertise in on the growing non-Apple platforms. Publishers are turning to the mobile Web because they're sick of remaking the same app for different devices. HTML5 is a solution for both (see our post, "HTML5 is Great for Mobile, Developers Say").

Rich media ads get a 56% higher click-through rate than static ads, according to Greystripe. HTML5 promises a consistent and rich user experience across platforms, and it's often faster to present an ad with HTML5 even when it's being accessed by a Flash-capable device, said Greystripe founder and CEO Michael Chang.

Chang also said the bigger the ad, the more effective. Ads on the iPad get much higher engagement from users because they're bigger, he said.

Greystripe's move to mobile Web also protects the company if Apple ever decides to crack down on in-app advertising. Earlier this summer, Apple moved to block players like Google's AdMob from operating on its devices. Apple has since backed off, but there is no guarantee that it wouldn't change the rules again to favor its own in-app advertising network, iAd. By contrast, Apple has no control over ads displayed on mobile websites.

In-app ads aren't going away, but the mobile Web and HTML5 present a compelling alternative.