Why won some video podcasts play on my iPod, iPhone, iPad or Apple TV?
Some video podcasts, while playable in iTunes, are encoded in formats that are not compatible with iPods, iPhone, iPads or Apple TV. To convert those videos so that they are compatible across different Apple platforms, highlight the downloaded video in your iTunes client, click on Advanced and select “Create iPod/iPhone/iPad/Apple TV Version”. iTunes will automatically re-encode the video for playback on your selected device. Go to the Movies section of your Library to find and play the converted episodes.