刚刚在avs文档中找到了这个
testcard = ColorBars()
# get a blue mask clip (the same blue as in ColorBars is used: R16 G16 B180)
maskclip = BlankClip(clip=testcard, color=$0f0fb4)
# Example subtitle file with blue backgroud as above
subs = ImageSource("F:\TestClips\blue.jpg").ConvertToRGB32
maskclip = ColorKeyMask(subs, $0f0fb4, 60)
Overlay(testcard, subs, mask=ShowAlpha(maskclip), mode="blend", opacity=1)
其中subs改成加载avi（可以用flash之类的做出来），然后colorkeymask里面设定透明色，再overlay上去，就可以了
