[FIXED] How to record the video from a webcam in a pyqt5 gui using OpenCV and QThread?

Issue

I'm trying to make pyqt5 Gui that shows a webcam live feed, records the feed at the same time, and saves it locally when closed. I managed to acheieve this using Timer(QTimer) in pyqt gui but When I try to implement it using Qthread (Which I really require) only the live feed is working.

Whenever I add Code required for recording video and run the program it says Python has Stopped Working and closes. Here is my Code:

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


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

    def run(self):
        self.cap = cv2.VideoCapture(0)

        self.width = int(self.cap.get(cv2.CAP_PROP_FRAME_WIDTH))
        self.height = int(self.cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

        self.codec = cv2.VideoWriter_fourcc('X', 'V', 'I', 'D')
        self.writer = cv2.VideoWriter('output.avi', self.codec, 30.0, (self.width, self.height))

        while self.cap.isOpened():
            ret, self.frame = self.cap.read()
            if ret:
                self.frame = cv2.flip(self.frame, 1)
                rgbimage = cv2.cvtColor(self.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 MyApp(QWidget):
    def __init__(self):
        super(MyApp, self).__init__()
        self.title = 'Camera'
        self.initUI()

    def initUI(self):
        self.label = QLabel(self)
        lay = QVBoxLayout()
        lay.addWidget(self.label)
        self.setLayout(lay)

        self.th = Thread()
        self.th.changePixmap.connect(self.setImage)
        self.th.start()
        self.show()

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


def main():
    app = QApplication(sys.argv)
    ex = MyApp()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

I tried placing the .write() inside the run() of Thread class as well which is showing the same error. Can you guys point out What I'm doing wrong and how to make it work. I'm new to python and pyqt. Thanks in Advance.

Solution

You need to separate threads. First thread is for signal, second is for the record and the main thread is for GUI. Try the following code. There is a button to start/stop the record.

import sys
import cv2

from PyQt5.QtWidgets import QApplication, QWidget, QPushButton, QLabel, QVBoxLayout
from PyQt5.QtGui import QImage, QPixmap
from PyQt5.QtCore import QTimer, QThread, pyqtSignal, pyqtSlot
from PyQt5 import QtWidgets, QtCore, QtGui

#https://ru.stackoverflow.com/a/1150993/396441

class Thread1(QThread):
    changePixmap = pyqtSignal(QImage)
    
    def __init__(self, *args, **kwargs):
        super().__init__()

    def run(self):
        self.cap1 = cv2.VideoCapture(0, cv2.CAP_DSHOW)
        self.cap1.set(3,480)
        self.cap1.set(4,640)
        self.cap1.set(5,30)
        while True:
            ret1, image1 = self.cap1.read()
            if ret1:
                im1 = cv2.cvtColor(image1, cv2.COLOR_BGR2RGB)
                height1, width1, channel1 = im1.shape
                step1 = channel1 * width1
                qImg1 = QImage(im1.data, width1, height1, step1, QImage.Format_RGB888)
                self.changePixmap.emit(qImg1)

class Thread2(QThread):
    
    def __init__(self, *args, **kwargs):
        super().__init__()
        self.active = True

    def run(self):
        if self.active:            
            self.fourcc = cv2.VideoWriter_fourcc(*'XVID') 
            self.out1 = cv2.VideoWriter('output.avi', self.fourcc, 30, (640,480))
            self.cap1 = cv2.VideoCapture(0, cv2.CAP_DSHOW)
            self.cap1.set(3, 480)
            self.cap1.set(4, 640)
            self.cap1.set(5, 30)
            while self.active:                      
                ret1, image1 = self.cap1.read()
                if ret1:
                    self.out1.write(image1)     
                self.msleep(10)                      

    def stop(self):
        self.out1.release()

       
class MainWindow(QWidget):
    
    def __init__(self):
        super().__init__()
        self.resize(660, 520)
        self.control_bt = QPushButton('START')
        self.control_bt.clicked.connect(self.controlTimer)
        self.image_label = QLabel()
        self.saveTimer = QTimer()
        self.th1 = Thread1(self)
        self.th1.changePixmap.connect(self.setImage)
        self.th1.start()
        
        vlayout = QVBoxLayout(self)
        vlayout.addWidget(self.image_label)
        vlayout.addWidget(self.control_bt)   

    @QtCore.pyqtSlot(QImage)
    def setImage(self, qImg1):
        self.image_label.setPixmap(QPixmap.fromImage(qImg1))

    def controlTimer(self):
        if not self.saveTimer.isActive():
            # write video
            self.saveTimer.start()
            self.th2 = Thread2(self)
            self.th2.active = True                                
            self.th2.start()
            # update control_bt text
            self.control_bt.setText("STOP")
        else:
            # stop writing
            self.saveTimer.stop()
            self.th2.active = False                   
            self.th2.stop()                         
            self.th2.terminate()                    
            # update control_bt text
            self.control_bt.setText("START")

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

Answered By - Alex