Using a four channel Blackmagic Design Decklink card (such as the Duo 2), WAGS2 will output separate key and fill signals for output channel one, and a full screen combined signal for channel two. Normally, the key and fill signals are sent to your switcher or vision mixer’s downstream key inputs. The other channel would be sent to a source input on your switcher.
If your switcher does not have downstream key capability, you can configure WAGS2 for internal keying. In this case, you would send a clean program feed into WAGS2, which would return a combined program+graphics feed. These two connections would replace the key and fill connections. The other full screen output would be unchanged.
You can connect an external video source to WAGS2 using the fourth channel on the Decklink card. This can be used as a source in WAGS2, and combined with graphics or other media before being sent back out on one of the other two channels.
If your hardware supports it, embedded audio can be sent along with the video on the SDI connections in and out of the Decklink card.