code: def zero_crossing_rate(frame):
      """Computes zero crossing rate of frame"""
      count = len(frame)
      count_zero = np.sum(np.abs(np.diff(np.sign(frame)))) / 2
      return np.float64(count_zero) / np.float64(count - 1.0)
  
imports: from __future__ import print_function
  import math
  import numpy
  import sys
  from scipy.fftpack import fft
  import matplotlib.pyplot
  from scipy.signal import lfilter
  from scipy.fftpack.realtransforms import dct
  from tqdm import tqdm
label_desc: Use image node_id 2 for calling a global function with example usage: zero_crossing_rate(frame) and returns: unknown