如何检测特定对象何时在OPENCV程序中移出框架？

Question

我目前正在练习OPENCV并尝试了面部识别代码，并且工作正常。如果我离开屏幕超过2分钟，我想通知。当我不在时，我正在尝试播放音频文件，并在回来时停止它。

import cv2 as cv
import sys

cascPath = sys.argv[1]
faceCascade = cv2.CascadeClassifier(cascPath)

video_capture = cv.VideoCapture(0)

while True:
    # Capture frame-by-frame
    ret, frame = video_capture.read()

    gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)

    faces = faceCascade.detectMultiScale(
        gray,
        scaleFactor=1.1,
        minNeighbors=5,
        minSize=(30, 30),
        flags=cv.CASCADE_SCALE_IMAGE  
    )

    # Draw a rectangle around the faces
    for (x, y, w, h) in faces:
        cv.rectangle(frame, (x, y), (x+w, y+h), (0, 255, 0), 2)

    # Display the resulting frame
    cv.imshow('Video', frame)
    
    # check if the tuple faces is empty
    if len(faces) == 0:
      start_time = time.time()
      while len(faces) == 0:
        print('person is away for ',time.time()-start_time)
        d_time = time.time()
        if d_time-start_time > 120:
            pygame.mixer.init()
            sound = pygame.mixer.Sound("Recording.mp3")
            sound.play(5)

    if cv.waitKey(1) & 0xFF == ord('q'):
        break

video_capture.release()
cv.destroyAllWindows()