The podcast hosting company Blubrry said today that it has released a new tool for professional podcasters using its service that will allow them to dynamically insert a commercial into a show. That ability, already in use by some other podcast and streaming media companies, allows a podcaster to change ads in past and current episodes. Not only does it open up a show to an advertiser that may want to run commercials with updated messages, but dynamic insertion also allows podcasters to better target advertising to listeners.

“Podcast advertising revenue is expected to reach $1 billion by 2021,” said Todd Cochrane, CEO of RawVoice/Blubrry in the announcement. “By releasing dynamic insertion, we’re ensuring that our podcasting community is able to better monetize their podcast.”

For now Blubrry is limiting dynamic ad insertion to professional podcasters. The first update provides free pre-roll advertisements for the latest 50 episodes published. The company says later this month it will release an updated version that will allow for unlimited pre, mid, and post-roll ads for a monthly fee. And then later this year another update in the works will allow for geographic targeting.