code: def fadein(clip, duration, initial_color=None):
      """Makes the clip progressively appear from some color (black by default),
      over ``duration`` seconds at the beginning of the clip. Can be used for
      masks too, where the initial color must be a number between 0 and 1.
  
      For cross-fading (progressive appearance or disappearance of a clip
      over another clip, see ``transfx.crossfadein``
      """
      if initial_color is None:
          initial_color = 0 if clip.is_mask else [0, 0, 0]
  
      initial_color = np.array(initial_color)
  
      def filter(get_frame, t):
          if t >= duration:
              return get_frame(t)
          else:
              fading = 1.0 * t / duration
              return (
                  fading * get_frame(t) + (1 - fading) * initial_color
              )
  
      return clip.transform(filter)
  
label_desc: Use image node_id 1 for calling a global function with example usage: fadein(clip, duration, initial_color) and returns: clip, get_frame, unknown