code: def mark_poi(self, times=None):
          
          y_pos = BARS['quality']['pos0']
          height = 5
          
          for rect in self.idx_poi:
              self.scene.removeItem(rect)
          self.idx_poi = []
          
          if not times:
              return
          
          for beg, end in times:
              rect = QGraphicsRectItem(beg, y_pos, end - beg, height)
              rect.setPen(NoPen)
              rect.setBrush(Qt.darkRed)
              self.scene.addItem(rect)
              self.idx_poi.append(rect)
docs: Mark selected signal, from list of start and end times.
          
          Parameters
          ----------
          times : list of tuple of float
              start and end times, in sec form rec start