I have been doing some podcasting/vodcasting experimentation on another blog to see what file types WordPress will automatically make an enclosure tag for. I also wanted to see what Feedburner picked up and recognized since I am using that to send my podcast/vodcast RSS feeds out. Please bare in mind that I am on a Mac (running Tiger OS X 10.4) and the methods I used might be slightly different than if I were on a PC creating and testing this out. The one audio type I know that WP makes an enclosure for is a .mp3 file. These can play on any mp3 player (including iTunes) and iTunes recognized the RSS feed and so did my other program Juice (cross platform RSS feed reader, formally known as iPodder). So to be safe, make your podcasts in an mp3 file format to ensure most of your listeners can download and hear it. WordPress made the enclosure tags automatically and Feedburner picked it up instantly. Thumbs up for mp3! Also, if you use Audacity (open source cross-platform audio-editing software) you can save your .mp3's as .ogg files. They are slightly smaller files and the quality is still there. Wp automatically makes enclosures for .ogg files as well, and Feedburner can read the RSS and iTunes will play .ogg files. Thumbs up for .ogg files too!
For vodcasting, I tested the 4 basic video formats that almost ever computer can play via their favorite media player. I tested an AVI (mpeg-4), MOV (an mpeg-4 file encapsulated in QT), WMV (Windows Media Video), and an RM (RealPlayer Media file). I used iMovie HD to export my AVI files as a WMV and RM and I installed the RealPlayer 10 Real Export Plug-in for Mac OSX to export the RM file out of iMovie HD (even though the website said it wouldn't work w/ Tiger, I tried it anyway and it did work and it's free to download!). I used ffmpegx to make my AVI into an MOV (mpeg-4 format). I started out with AVI's because the screencasts were made on a PC using CamStudio (open source screencasting programs for Linux and Windows). It was my job to make them into vodcasts, just in case you were wondering ;-). WordPress automatically made an enclosure tag for the AVI, MOV, and RM files. These files were also read instantly by Feedburner. The MOV file was the only one that played in iTunes, and Juice recognized the AVI, RM, and MOV files (but only played the MOV because it uses iTunes as the default player). WP didn't make an enclosure for the WMV, and Feedburner didn't recognize it with a play button (but it had the URL to click on to play).
So if you want to vodcast, I suggest using MOV (mpeg-4), AVI (mpeg-4), or a RM file. These will be read by the RSS feed reader and automatically have enclosure tags so your viewers can see your current vodcasts. Also if you want to make a WMV file on a Windows machine, use the Windows Media Encoder (free download), and if you want to make RM files, download the free Basic RealMedia Producer for Windows off of the RealNetworks site. You should be good to go. Happy pod/vodcasting!