def METHOD_NAME(self, btn):
    if btn == self.playbtn:
        self.label.setText("Play video")
        if self.progress_slider.value() == self.cap.get(7) - 1:
            self.slider_frame_num = 0
            self.progress_slider.setValue(self.slider_frame_num)
            self.time_label.setText('{}/{}'.format(self.slider_frame_num, self.cap.get(7)))
        self.timer_camera = QTimer()  # 定义定时器
        self.timer_camera.start(1000 / self.cap.get(cv2.CAP_PROP_FPS))
        self.slider_frame_num = self.progress_slider.value()
        self.timer_camera.timeout.connect(self.open_frame)
    elif btn == self.pushButton_2:
        self.label.setText("Stop video")
        self.slot_stop()
    elif btn == self.pushButton_4:
        self.label.setText("Choose video")
        self.select_video_path, _ = QFileDialog.getOpenFileName(self.frame, "Open", "", "*.mp4;;All Files(*)")
        print("-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-")
        print("Select video file path:\t" + self.select_video_path)
        # ToDo To AP-kai:下断点来看一下，如果不选择的时候返回值是什么样的，然后再做判断，目前这个if没有生效
        if self.select_video_path != "":
            self.cap = cv2.VideoCapture(self.select_video_path)
            # 存所有frame
            self.save_temp_frame()
            print("save temp frame done")
            self.progress_slider.setRange(0, self.cap.get(cv2.CAP_PROP_FRAME_COUNT))
            self.slider_frame_num = 0
            self.open_frame()
        # ToDo To AP-kai: 未来这个地方增加提示框，告诉他没有选择文件