docs: def row_value(self, row):
          """Get the tracks value at row"""
          irow = int(row)
          i = self._get_key_index(irow)
          if i == -1:
              return 0.0
  
          # Are we dealing with the last key?
          if i == len(self.keys) - 1:
              return self.keys[-1].value
  
          return TrackKey.interpolate(self.keys[i], self.keys[i + 1], row)