code: def get_used_key_frames(self):
          
  
          skl = self.key_frame_list.sorted_key_list()
          # each element in used_key_frames is a tuple (key_name, key_dict)
          used_key_frames = []
          for kf in skl:
              if kf in self.dct['keys']:
                  used_key_frames.append((kf, self.dct['keys'][kf]))
          return used_key_frames
docs: Returns a list of the keyframes used by this channel, sorted with
          time. Each element in the list is a tuple. The first element is the
          key_name and the second is the channel data at that keyframe.