Helpfully, they also suggest for vodcasters
"uses some ultra-sophisticated voice recognition software to create a rough transcript.
"That transcript is rough -- definitely not good enough to publish, so it's a good thing Podzinger doesn't publish it. However, it is good enough to yield fairly accurate search results. So anyone searching for keywords at Podzinger turns up audio files which match that query."
"if you publish video content, you can still leverage Podzinger. First, create a feed and make sure that every time you produce an audio file, it gets added to that feed. For video, screencasts, etc., extract the audio in MP3 format, and then add those MP3 files to your feed. Then register that feed in Podzinger. You don't have to advertise this feed to the general audience, you can use it just for Podzinger if you want."
UPDATE: Poynter have added some more resources for improving audio listings from reader Anthony Anderson:
"Blinkx: Keyword searching of audio and video. Submit your site to Blinkx.
Podscope: Audio/video search engine. Like Podzinger, but it's been around longer. Podscope powers AOL's podcast search. Submit your site to Podscope.
TVeyes: Fee-based service (real-time transcript searching of network TV, local stations, NPR, and more). Parent of Podscope. Also offers a free keyword
search service for full text (transcript search) of Web-based news video. "