I have a WD TV Live device with an external USB HD attached. What additional products do I need to be able to stream video stored on the USB drive to a second TV in the house? Will WD TV Play do this if connected to the 2nd TV?
No, the WD TV Play will be unable to access the videos since the WD TV Live does not have a DLNA server.
Another WD TV Live should be able to access them, though, via a network share connection.
