code: def n_frames_total(self, stride=1, skip=0):
          r
          if not IteratorState.is_uniform_stride(stride):
              return len(stride)
  
          return sum(self.trajectory_lengths(stride=stride, skip=skip))
docs: r"""Returns total number of frames.
  
          Parameters
          ----------
          stride : int
              return value is the number of frames in trajectories when
              running through them with a step size of `stride`.
          skip : int, default=0
              skip the first initial n frames per trajectory.
          Returns
          -------
          n_frames_total : int
              total number of frames.