@requires_duration
@add_mask_if_none
def crossfadeout(clip, duration):
 newclip = clip.copy()
 newclip.mask = clip.mask.fx(fadeout, duration)
 return newclip

@ requires_duration @ add_mask_if_none def crossfadeout ( clip , duration ) : newclip = clip . copy ( ) newclip . mask = clip . mask . fx ( fadeout , duration ) return newclip
makes the clip disappear progressively .