'Add a mask VideoClip to the VideoClip.
Returns a copy of the clip with a completely opaque mask
(made of ones). This makes computations slower compared to
having a None mask but can be useful in many cases. Choose
Set ``constant_size`` to  `False` for clips with moving
image size.'

def add_mask(self):

    if self.has_constant_size:
        mask = ColorClip(self.size, 1.0, ismask=True)
        return self.set_mask(mask.set_duration(self.duration))
    else:
        make_frame = (lambda t: np.ones(self.get_frame(t).shape[:2], dtype=float))
        mask = VideoClip(ismask=True, make_frame=make_frame)
        return self.set_mask(mask.set_duration(self.duration))
