How hot is podcasting? Stupid V.C. money hot. Podcast advertising expanded at a 48 percent rate last year, and it’s forecast to grow about 25 percent a year through 2020. By that point, it would be approaching half a billion dollars in annual ad revenue. That growth is very reminiscent of the old IAB charts of Internet advertising we saw at the turn-of-the-century: tiny numbers growing explosively. Podcasts have joined the digital text and video as a prominent new media form of its own — a format for storytelling that is connecting with a broad audience.