class_docstr: Video output implemented by writing individual PNGs to disk.
class_docstr_tok: ["Video","output","implemented","by","writing","individual","PNGs","to","disk","."]
code: def emit_frame(self, np_array):
      filename = self.directory + "/{:05}.png".format(self.frame_num)
      self._write_image(np_array.astype(np.uint8), filename)
      self.frame_num += 1
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import abc
  import os
  import subprocess
  import time
  import numpy
label_desc: Use image node_id 3 for calling the PNGVideoOutput obj's underlying member method code with example usage: obj.emit_frame(np_array) without return types