freeze_ratio.py reports error "float division by zero" when analyzing an mp4 file

[13905182381]

see log as below

root@Intel-9-95:/QoSTestFramework/analysis/python# python freeze_ratio.py ../dataset/output/yuanshen.mp4
ffmpeg -i ../dataset/output/yuanshen.mp4 -vf mpdecimate=0:768:320:0.33000 -loglevel debug -an -f null - 2>&1
Traceback (most recent call last):
File "freeze_ratio.py", line 188, in
main(sys.argv)
File "freeze_ratio.py", line 177, in main
g_input, max_drop_count, hi, lo, frac, freeze_threshold)
File "freeze_ratio.py", line 125, in extrace_freeze
float(_output_frame_num))/float(_input_frame_num)
ZeroDivisionError: float division by zero
root@Intel-9-95:/QoSTestFramework/analysis/python#