Most efficient way to xfade on GPU (to get alpha effects)

Hello

I've got a matrix of videos which will be triggered by osc at different times on different videoplanes, and i want to make each instance semi-transparent (different values, different times). So I need a fading effect.

Yes there are other places I've seen on the web which describe xfading (not least the fm) but I've not found a decent resource which shows me how to do it on the GPU. Is this even place for it? Also I'm guessing as I'm using uyvy for performance reasons I need to using the first value in that colorspace to 0 to remove luminance - not sure how to do that yet either.

Objects like charmap would be good, but again, I'd like to get the GPU in on this and I don't think that's the way it was designed.

I have the attached abstraction which is taking a uyvy jit.qt.movie and a argb jit.matrix (not worked out how to convert it yet) and running them through a xfade and then into a slab (@file cc.uyvy2rgba.lite.jxs) and from there a videoplane. I guess the conflicting colorspaces are the reason it wasnt working but I've then tried with a 1 frame black qt movie of the correct dims and that doesn't work either. The patch for that is second. Can anyone else comment on the best way to get what I'm after?

Patch is:

tried with short, black qt movie: