code: def make_image_key(video_id, timestamp):
      """Returns a unique identifier for a video id & timestamp."""
      return "%s,%04d" % (video_id, int(timestamp))
  
file_path: SlowFast/slowfast/utils/ava_eval_helper.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import csv
  import logging
  import pprint
  import time
  from collections import defaultdict
  import numpy
  import slowfast.utils.distributed
  from ava_evaluation import object_detection_evaluation, standard_fields
  from slowfast.utils.env import pathmgr
label_desc: Use image node_id 1 for calling a global function with example usage: make_image_key(video_id, timestamp) and returns: unknown