Remember podcasting?

While marketers have been busy uploading commercials to YouTube, the once-buzzed-about medium has spent the past two years building its audience and enhancing advertising capability.

Now, podcasts are finally poised to grab a larger slice of the multibillion-dollar online advertising pie.

Research firm eMarketer expects that advertisers will spend more than $400 million on podcasting by 2011, up from $80 million last year.

Fueling the anticipated growth is the expected entrance of Google into the podcasting arena, as well as new podcasting services focused on answering advertisers’ most pressing questions: How many people are tuning in to the hundreds of thousands of online podcasts, and who are they?

The medium isn’t waiting for Google, however. Podcast company Podtrac unveiled a free online service that enables advertisers to research audience information for audio and video podcasts based on demographics, size, and other characteristics.

The company, which helps connect roughly 5,000 of the top podcasters to advertisers, includes data for all podcasts in its new service, including those from major media companies with whom Podtrac is not affiliated. It indexes its data to information in Mediamark Research’s Survey of the American Consumer.

Photo by Troy McClure SF.