code: def get_video_start_time(video_file):
      
      if not os.path.isfile(video_file):
          print("Error, video file {} does not exist".format(video_file))
          return None
      video_end_time = get_video_end_time(video_file)
      duration = get_video_duration(video_file)
      if video_end_time == None or duration == None:
          return None
      else:
          video_start_time = (
              video_end_time - datetime.timedelta(seconds=duration))
          return video_start_time
docs: Get start time in seconds