The HD Connect port on the back of your Slingbox PRO is designed specifically to work in tandem with the Sling Media HD Connect cable. If you plug your HD device directly into the Slingbox PRO without using the HD Connect cable, the Slingbox will not recognize the video signal coming from that device; it will behave as if nothing were connected to the port at all.
The HD Connect cable enables you to watch your home television’s HD programming (up to 1080i) by connecting your HD component device to the Slingbox. The Slingbox and SlingStream technology adapts the compressed video stream to match the available network and Internet bandwidth to provide the best possible video quality between the Slingbox and the SlingPlayer application, whether running on a computer or mobile phone.
The HD Connect cable also:
Provides pass-through connectors, so you can easily add the cable into existing HD configurations.
Provides component video and stereo audio connections.