PyQtでwebカメラを使って動画を録画し，保存するアプリでエラーが発生してしまいます

下のpyqt5で書かれたwebカメラから映像を取得し保存するアプリで，最初にendボタンを押すと
'NoneType' object has no attribute 'deleteLater'
とエラーが出てしまいます．これを解決する方法を教えてくださるとありがたいです．

python3
1import sys
2from PyQt5 import QtCore, QtGui, QtWidgets
3import cv2
4import os, zipfile, datetime
5now = datetime.datetime.now()
6dirname = 'test_{0:%Y%m%d}'.format(now)
7
8class QtCapture(QtWidgets.QWidget):
9    def __init__(self, *args):
10        super(QtWidgets.QWidget, self).__init__()
11
12        self.fps = 24
13        self.cap = cv2.VideoCapture(*args)
14
15        self.video_frame = QtWidgets.QLabel()
16        lay = QtWidgets.QVBoxLayout()
17        lay.setContentsMargins(0,0,0,0)
18        lay.addWidget(self.video_frame)
19        self.setLayout(lay)
20
21        # ------ Modification ------ #
22        self.isCapturing = False
23        self.ith_frame = 1
24        # ------ Modification ------ #
25
26    def setFPS(self, fps):
27        self.fps = fps
28
29    def nextFrameSlot(self):
30        ret, frame = self.cap.read()
31
32        # ------ Modification ------ #
33        # Save images if isCapturing
34        if self.isCapturing:
35            if not(os.path.isdir(dirname)):
36                os.mkdir(dirname)
37            cv2.imwrite('./'+dirname+'/img_%05d.jpg'%self.ith_frame, frame)
38            self.ith_frame += 1
39        # ------ Modification ------ #
40
41        # My webcam yields frames in BGR format
42        frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
43        img = QtGui.QImage(frame, frame.shape[1], frame.shape[0], QtGui.QImage.Format_RGB888)
44        pix = QtGui.QPixmap.fromImage(img)
45        self.video_frame.setPixmap(pix)
46
47    def start(self):
48        self.timer = QtCore.QTimer()
49        self.timer.timeout.connect(self.nextFrameSlot)
50        self.timer.start(1000./self.fps)
51
52    def stop(self):
53        self.timer.stop()
54
55    # ------ Modification ------ #
56    def capture(self):
57        if not self.isCapturing:
58            self.isCapturing = True
59        else:
60            self.isCapturing = False
61    # ------ Modification ------ #
62
63    def deleteLater(self):
64        self.cap.release()
65        super(QtWidgets.QWidget, self).deleteLater()
66
67
68class ControlWindow(QtWidgets.QWidget):
69    def __init__(self):
70        QtWidgets.QWidget.__init__(self)
71        self.capture = None
72
73        self.start_button = QtWidgets.QPushButton('Start')
74        self.start_button.clicked.connect(self.startCapture)
75        self.quit_button = QtWidgets.QPushButton('End')
76        self.quit_button.clicked.connect(self.endCapture)
77        self.end_button = QtWidgets.QPushButton('Stop')
78
79        # ------ Modification ------ #
80        self.capture_button = QtWidgets.QPushButton('Capture')
81        self.capture_button.clicked.connect(self.saveCapture)
82        # ------ Modification ------ #
83
84        vbox = QtWidgets.QVBoxLayout(self)
85        vbox.addWidget(self.start_button)
86        vbox.addWidget(self.end_button)
87        vbox.addWidget(self.quit_button)
88
89        # ------ Modification ------ #
90        vbox.addWidget(self.capture_button)
91        # ------ Modification ------ #
92
93        self.setLayout(vbox)
94        self.setWindowTitle('Control Panel')
95        self.setGeometry(100,100,200,200)
96        self.show()
97
98    def startCapture(self):
99        if not self.capture:
100            self.capture = QtCapture(0)
101            self.end_button.clicked.connect(self.capture.stop)
102            # self.capture.setFPS(1)
103            self.capture.setParent(self)
104            self.capture.setWindowFlags(QtCore.Qt.Tool)
105        self.capture.start()
106        self.capture.show()
107
108    def endCapture(self):
109        self.capture.deleteLater()
110        self.capture = None
111
112    # ------ Modification ------ #
113    def saveCapture(self):
114        if self.capture:
115            self.capture.capture()
116    # ------ Modification ------ #
117
118
119
120if __name__ == '__main__':
121
122    import sys
123    app = QtWidgets.QApplication(sys.argv)
124    window = ControlWindow()
125    sys.exit(app.exec_())
126