Originally Posted by Burd Man
I have a brand new 55" Panasonic plasma. Not sure of the model. Then there is a Toshiba VGA projector that is old...and I don't know the model.
Then one of my concerns with trying to feed both from a single output may be valid.
One concern is what resolution do you send to two displays with not only different native formats and resolutions but likely different compatible resolutions? The Panasonic plasma is likely 1920x1080 native resolution and will probably accept a 1024x768 image and pillarbox it but the Toshiba projector is likely 1024x768 or similar and may or may not accept a 1920x1080 signal and letterbox it. Unless there is a device involved that can provide intermediate scaling, you'll probably have to set the computer to provide an output that both the plasma and projector can directly accept and display.
Related to the above is EDID. EDID allows a computer and attached display to communicate and automatically configure the computer video output for the attached display. That's great for a single display but introduces additional challenges when addressing multiple attached display devices. For example, the computer may 'see' the plasma display and configure its output based on the optimal settings for that specific device, which may result in the computer outputting a signal that is not compatible with the projector. So unless you can set the display devices or some intermediate devices to provide EDID information compatible for both the flat panel and the projector then you may have to override any automatic settings and manually set the computer video settings to something all attached displays can support.
Finally, some Apple devices are very touchy about HDCP content protection and if they see an HDCP compliant device connected, which the plasma likely is, then the computer may enable HDCP regardless of whether the content calls for it. When the HDCP 'handshake' then occurs and the computer sees two attached display devices it may react in different ways. If one of the attached devices is HDCP compliant while the other is not one possible result is the computer simply refusing to provide an output.
So it may be as simple as manually configuring the computer to output a signal compatible for both displays or it may be a virtual impossibility without some intermediate processing and conversion.
The USB-to-video device is essentially providing a dedicated additional output for one of the displays so you are not having two different display devices on the same output.