screenshot
              Allows  acquiring screenshots of the movie using slave mode com-
              mands that can be bound to keypresses.  See the slave mode docu-
              mentation  and  the  INTERACTIVE  CONTROL  section  for details.
              Files named 'shotNNNN.png' will be saved in the working directo-
              ry,  using  the  first available number - no files will be over-
              written.  The filter has no overhead when not used  and  accepts
              an arbitrary colorspace, so it is safe to add it to the configu-
              ration file.