You CANNOT play purchased HD movies from iTunes to external monitors, via DVI, HDMI, DP. -- CANNOT. It's protected. Apple designed it that way.
You can play them though on your iphone, ipad, iMac, Macbook built-in monitors... i.e. devices with built-in monitors.
What you can do is right click on the title and select view it as SD video.
heck, even on a real iMac, if you have a 2nd external monitor connected that is non HDCP, it will not play HD movies... until you unplug the 2nd monitor. Even if you have a Macbook, and you connect an external projector, it will not play the HD movie, until you unplug the projector.
这是老外说的，外接显示器必须支持hdcp，即使是真iMac，如果外接显示器不能支持hdcp，也不能播hd。你检查一下你的显示器是否支持hdcp。
另外，请问楼主你的配置是什么，能正常播标清？现在我的黑苹果，连没有任何保护的预告片都不能播，进度条完全不动。
我的CPU是i7 4790，显卡hd7950，主板z97x-ud3h
