import cv2

car_cascade = cv2.CascadeClassifier('cars.xml')
cap =cv2.VideoCapture('car3.mp4')

frame_width = int(cap.get(3))
frame_height = int(cap.get(4))

out = cv2.VideoWriter('output.avi',cv2.VideoWriter_fourcc('M','J','P','G'), 10, (frame_width,frame_height))

while True:
    ret, frame = cap.read()
    if ret:
        gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        cars = car_cascade.detectMultiScale(gray, 1.3, 5)
        for(x, y, w, h) in cars:
            cv2.rectangle(frame, (x,y), (x+w, y+h), (255,0,0), 2)

        cv2.imshow('Car Detection', frame)
        out.write(frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break
    else:
        break

cap.release()
out.release()
cv2.destroyAllWindows()