def apply(self, clip: Clip) -> Clip:
        """Apply the effect to the clip."""

        def stereo_volume(get_frame, t):
            frame = get_frame(t)
            if len(frame) == 1:  # mono
                frame *= self.left if self.left is not None else self.right
            else:  # stereo, stereo surround...
                for i in range(len(frame[0])):  # odd channels are left
                    frame[:, i] *= self.left if i % 2 == 0 else self.right
            return frame

        return clip.transform(stereo_volume)
Apply the effect to the clip.
moviepy/audio/fx/MultiplyStereoVolume.py