Screen recorder + object detector (python)

import numpy as np
from PIL import ImageGrab
import cv2

def draw_detections(img, rects, thickness = 1):
    for x, y, w, h in rects:
        pad_w, pad_h = int(0.15*w), int(0.05*h)
        cv2.rectangle(img, (x+pad_w, y+pad_h), (x+w-pad_w, y+h-pad_h), (0, 255, 0), thickness)

hog = cv2.HOGDescriptor()
hog.setSVMDetector( cv2.HOGDescriptor_getDefaultPeopleDetector() )
cap=cv2.VideoCapture('vid.avi')
while(True):
    screen =  np.array(ImageGrab.grab(bbox=(0,40,800, 640)))
    #screen = cv2.Canny(screen ,threshold1 = 200,threshold2 = 200 )
    found,w=hog.detectMultiScale(screen, winStride=(8,8), padding=(32,32), scale=1.05)
    draw_detections(screen,found)
    cv2.imshow('window',screen)
    if cv2.waitKey(25) & 0xFF == ord('q'):
        cv2.destroyAllWindows()
        break