I feel like vMix can already do this, but I am having a terrible time getting it to work. I have a video source that has a separate alpha channel (coming in as a second source). How can I get vMix to see the alpha input and use as a key for the source input?

I select the settings of the "source" and under the colour key tab I tell the key/fill input to be "alpha". Do I need to adjust any other settings to make this work properly? Am I supposed to do it the opposite way, selecting the "source" as the key/fill source for "alpha"?

I feel like I've tried all the different combinations but still can't get it to composite properly. Any input is appreciated!!

Windows 7 Pro
Source Input is from a 4K computer feeding a Blackmagic capture card being cropped by vMix to see only one 1920x1080 quadrant
Alpha Input is a VIRTUAL input from the same 4K computer feed also cropped by vMix
A third input (not mentioned in this post) is a from a video camera via another Blackmagic capture card

-Matt

Yes vmix should be able to do this already. All you have to do is have your second source containing the alpha matte (i.e. black and white mask) selected as the fill/key input on the input you intend to key out. Make sure your input is also correct, try inverting the black and white portions. Last thing should be to enable the input (the one with color and graphics, not alpha) on an overlay channel, as icestream said.

I have been successful in using a motion video input as a luma mask for another video input. I just need to create a black & white motion video to do it like I want.

I can try to put together a short video demonstration/tutorial if this is what your after. Not sure how soon I could do it is the only thing. I've got a lot going on at the time being. Getting my PC reloaded after my windows 10 dual boot failure and prepping for an upcoming event.

Alright, Hope this is enough...
http://forums.vmix.com/d...p;m=23040&#post23040

The way it is currently setup, the luma mats as pictures are fading between to provide some simulated movement. The import thing is white passes image data thru, Black Blocks, and shades of grey will pass various shades in between. Brighter grays more, darker less.

A grey-scale video should do the same as what I provided here. I used an animated video background loop as a lum mask, but it wasn't black & white. It was full color. I could see the effect on the main video output. It was like a mid-tone grey-scales.

I don't actually have a true Black, White, Grey-scale video to verify, but I wouldn't think the way Martin has this configured, that it would treat the luma input differently because its a video or straight image. A video is nothing more than a stream of image sequences. The photos method I used would be considered an image sequence. If you have a video you want to use for luma, perhaps you should try to export it as a series a frames for an image sequence, and see if it does indeed work better.

BTW, what are the undesired results? That might help in figuring this out. I'm not sure I understand what your trying to do.

My situation was to create a live animation border around multiple webcam inputs originally, but the mask was not animated as it is with my demonstration, So this was inspired from that experimentation as the natural progression. I will be doing something like this myself in April if I can get the mask video created. I'd like to do something like a water bubble floating through the air with smoothed edges. Might try using a morphing software to fill in between main images.