code: def blink(clip, duration_on, duration_off):
      """
      Makes the clip blink. At each blink it will be displayed ``duration_on``
      seconds and disappear ``duration_off`` seconds. Will only work in
      composite clips.
      """
      new_clip = clip.copy()
      if new_clip.mask is None:
          new_clip = new_clip.with_mask()
      duration = duration_on + duration_off
      new_clip.mask = new_clip.mask.transform(
          lambda get_frame, t: get_frame(t)
          * ((t % duration) < duration_on)
      )
      return new_clip
  
label_desc: Use image node_id 1 for calling a global function with example usage: blink(clip, duration_on, duration_off) and returns: new_clip