Airplay on AppleTV: no picture only sound

I can get AirPlay on my iPad to play only one type of video on AppleTV, YouTube. But nothing else works. Any other video, for example from New York Times app, the WSJ app, Netfix or from the iPad PBS app, even though they give me the option to select AppleTV, I get only sound and no video on AppleTV. The Airplay icon does appear on the ATV screen but says Unknown/Untitled and only provide sound but no picture. I've updated everything, ATV (just last night), my iMac (last week) and my iPad and iPhone (both yesterday afternoon). Each component has the latest software updates. Still the only video I can view using AirPlay from my iPad is YouTube, which is already an option of the ATV menu. So what's the point of Airplay? Am I missing something?