Roku setup

[Joe30]

I have a Roku plugged into both an LGTV and a (formerly) computer monitor (hp if that matters). The idea is to be able to play Roku from both screens at once, or (more usefully) just whichever one I have on with the input set to that hdmi. The Roku output is in an hdmi splitter cable which has one cable going to the computer monitor and one going to the LGTV screen. That way, in theory, I should be able to set the LGTV input to something else while Roku keeps playing from the computer monitor next to it. 

The problem is, it doesn’t work. Having both devices plugged into the splitter cable at the same time causes both screens to display incorrectly: the LGTV screen jumps every second or so between the actual Roku Home Screen , to static, to green, to black. Sometimes it cycles, and sometimes the green only appears once before being removed from the rotation (which remains Roku, static, black, repeat). The hp computer monitor simply doesn’t recognize any input at all. But when either screen is UNPLUGGED from the Roku device, neither problem occurs and the image displays correctly on the screen which remains plugged in. Am I misunderstanding something? Is there a right way to do this? Or is it just an intentional built in limitation that a Roku will only work if plugged into only one screen at once?

[makaiguy]

I have zero experience with HDMI splitter cables.

When you connect an HDMI output device to an HDMI input device, the two systems exchange information as to the capabilities of both devices and they negotiate mutually supported connection parameters that will allow the two to function together.  This exchange is called a "handshake".

I am guessing that a splitter cable connected to two display devices simultaneously will not permit two concurrent HDMI handshakes to take place, especially if the two display devices have different sets of capabilities (resolitions, supported features like Dolby, etc.)

You could connect the two displays to a single Roku through an HDMI switch that would allow you to switch back and forth between the two displays.

There are also HDMI splitter devices (as opposed to cables) where the splitter handles the handshake with the Roku and then is supposed to perform its own handhakes with the two displays.  I used to try to feed the output from a Directv receiver to two different rooms via such a splitter device but never had much success.