althor1138 said:
The base clip is the "bottom"clip in overlay. The overlay clip is the clip put on top of the base clip. the base clip is always the first clip entered into the overlay filter. So the base clip in the filter below should be your darkest clip, regardless of whether it's cap1 or cap2. If they are backwards, just flip them around.
Overlay(BASE clip,overlay clip,mode="luma",opacity=0.5)

Ok, that's clear. What about the first of the two scripts? this one...

reel1cap2 = avisource("PATH TO FILE")
reel1cap1 = avisource("PATH TO FILE")
blank=reel1cap1.blankclip()
inter=interleave(reel1cap2,reel1cap1,blank)
return(inter)

Does it matter which one is the darker ("base") clip?