code: def shift(self, *args, **kwargs):
          
          for item in self:
              item.shift(*args, **kwargs)
docs: shift(hours, minutes, seconds, milliseconds, ratio)
  
          Shift `start` and `end` attributes of each items of file either by
          applying a ratio or by adding an offset.
  
          `ratio` should be either an int or a float.
          Example to convert subtitles from 23.9 fps to 25 fps:
          >>> subs.shift(ratio=25/23.9)
  
          All "time" arguments are optional and have a default value of 0.
          Example to delay all subs from 2 seconds and half
          >>> subs.shift(seconds=2, milliseconds=500)