Video Playback speed is faster than expected pyQt5 and Opencv

Question

i am working on an Opencv project and when trying to add the gui for it, i wanted to use PyQt because i am familiar with it.

in this code

import cv2
import sys
from PyQt5.QtWidgets import  QWidget, QLabel, QApplication
from PyQt5.QtCore import QThread, Qt, pyqtSignal, pyqtSlot
from PyQt5.QtGui import QImage, QPixmap

class Thread(QThread):
    changePixmap = pyqtSignal(QImage)

def run(self):
    cap = cv2.VideoCapture("../Testing-Video.mp4")
    while True:
        ret, frame = cap.read()
        if ret:
            rgbImage = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
            h, w, ch = rgbImage.shape
            bytesPerLine = ch * w
            convertToQtFormat = QImage(rgbImage.data, w, h, bytesPerLine, 
            QImage.Format_RGB888)
            p = convertToQtFormat.scaled(640, 480, Qt.KeepAspectRatio)
            self.changePixmap.emit(p)


class App(QWidget):
    def __init__(self):
        super().__init__()
        self.left=0
        self.top=0
        self.width=600
        self.height=800
        self.initUI()

    @pyqtSlot(QImage)
    def setImage(self, image):
        self.label.setPixmap(QPixmap.fromImage(image))

    def initUI(self):
        self.setWindowTitle("Testing PyQt")
        self.setGeometry(self.left, self.top, self.width, self.height)
        self.resize(800, 600)
        # create a label
        self.label = QLabel(self)
        self.label.resize(640, 480)
        th = Thread(self)
        th.changePixmap.connect(self.setImage)
        th.start()
        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = App()
    ex.show()
    sys.exit(app.exec_())

which is something i didn't write myself, it's slightly adjusted from here , anyways using the Camera video capture, it works perfectly but when using any other video media, the playback is extremely fast, should i use a timer to call the frames constantly? better than using signal and slots?