We designed the Key/Fill SDI play out feature to work with Blackmagic Design hardware. We also tested it with the ATEM Television Studio which supports keying. It uses a method called premultiplied Key. mimoLive is therefore optimized for this mode of operation.
While working with a client who uses a different switcher brand, we noticed that the transparency didn't look quite right. Further investigation showed that that switcher is using a different keying which relies on a method inherited from analog switching systems. In this system, you set Clip and Gain values in your switcher that calculate how the key signal is interpreted.
In order to get this method to work the way you want, you have to find out the values for clip and gain in your switcher that produce the desired result. To help you do this, we have added an Alpha Channel Test pattern to the Video Output Test source you can use to play out and calibrate the settings in your switcher.