def fraction_of_second(self):
            if hasattr(self, '_m_fraction_of_second'):
                return self._m_fraction_of_second if hasattr(self, '_m_fraction_of_second') else None

            if self._time_base:
                self._m_fraction_of_second = self.raw_fraction_of_second / self._time_base

            return self._m_fraction_of_second if hasattr(self, '_m_fraction_of_second') else None