python - PyQt showing video stream from opencv

Question

Try to link PyQt and Opencv video feed, can't understand how to apply while loop for continuously streaming video. It just take a still picture.Please can anyone help to solve the problem.

• PtQt=5

• Python=3.6.1

---

class App(QWidget):
    def __init__(self):
        super().__init__()
        self.title = 'PyQt5 Video'
        self.left = 100
        self.top = 100
        self.width = 640
        self.height = 480
        self.initUI()


    def initUI(self):
        self.setWindowTitle(self.title)
        self.setGeometry(self.left, self.top, self.width, self.height)
        self.resize(1800, 1200)
        #create a label
        label = QLabel(self)
        cap = cv2.VideoCapture(0)
        ret, frame = cap.read()
        rgbImage = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
        convertToQtFormat = QtGui.QImage(rgbImage.data, rgbImage.shape[1], rgbImage.shape[0],
                                         QtGui.QImage.Format_RGB888)
        convertToQtFormat = QtGui.QPixmap.fromImage(convertToQtFormat)
        pixmap = QPixmap(convertToQtFormat)
        resizeImage = pixmap.scaled(640, 480, QtCore.Qt.KeepAspectRatio)
        QApplication.processEvents()
        label.setPixmap(resizeImage)
        self.show()

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

Answer 1

The problem is that the function that obtains the image is executed only once and not updating the label.
The correct way is to place it inside a loop, but it will result in blocking the main window. This blocking of main window can be solved by using the QThread class and send through a signal QImage to update the label. For example:

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(0)
        while True:
            ret, frame = cap.read()
            if ret:
                # https://stackoverflow.com/a/55468544/6622587
                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.initUI()

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

    def initUI(self):
        self.setWindowTitle(self.title)
        self.setGeometry(self.left, self.top, self.width, self.height)
        self.resize(1800, 1200)
        # create a label
        self.label = QLabel(self)
        self.label.move(280, 120)
        self.label.resize(640, 480)
        th = Thread(self)
        th.changePixmap.connect(self.setImage)
        th.start()
        self.show()