
# create a swap transition
black = BlankClip(width=clip1.Width,height=clip1.Height,color=color_black,length=clip1.FrameCount, fps=clip1.FrameRate)
white = BlankClip(width=clip1.Width,height=clip1.Height,color=color_white,length=clip1.FrameCount, fps=clip1.FrameRate)

# TopBottom->Center -Only EXPAND mode valid
tmask = LineAnim(black, white, h_start=clip1.Height, h_end=0)

# add clip1.FrameCount frames of the 2 clips
trans = Overlay(clip2, clip1, mask=tmask)
