As a vMix noob, I'm curious as to whether when sending key/fill grfx from vMix whether vMix generates its' own greyscale image from the title designer for a linear key? And am I correct in assuming, I need a seperate capture card to output that alpha channel/functionality, no way to do that say using the 2 fullscreen outputs? Right now I have the HD version, no way to examine alternatives.

Thanks for the interest and the heads-up. Partly, the question was whether the alpha in the .png generated by the GT title designer would work as a linear key signal for the ATEM. I extracted the 'alpha' in a GT title as a greyscale image in GIMP. Used the color/fill feed from vMix and the greyscale image was brought into the ATEM via the media player and voila, a clean key with subtle transparencies.