After playing with jitter for several hours, I realize that I suck a lot ;)
Basically, what I want is to be able to play 3 videos using 3 jit.qt.videoplane and to be able to fade any of the videoplanes so that I can see other videos behind it. (similar to having 3 layers in photoshop and setting the opacity for each layer) I tried with blend_enable 1 but it doesn’t seem to work. If the videos are on top of each other and I fade, the background will be black. It seems that even though color is at 0. 0. 0. 0., the plane is still opaque in the world.