from PyQt5.QtWidgets import QApplication, QWidget,\
    QLabel, QMainWindow, QGridLayout, QPushButton

from PyQt5.QtMultimedia import QAbstractVideoSurface, QAbstractVideoBuffer, QVideoFrame, QCamera
from PyQt5.QtCore import QObject, pyqtSignal, pyqtSlot
from PyQt5.QtGui import QImage, QPixmap

class frameGrabber(QAbstractVideoSurface):
    draw_image = pyqtSignal(QImage)
    process_image = pyqtSignal(QImage)

    def __init__(self, parent=None):
        super().__init__(parent)

    def supportedPixelFormats(self,handleType=QAbstractVideoBuffer.NoHandle):
         formats = [QVideoFrame.PixelFormat()]
         if (handleType == QAbstractVideoBuffer.NoHandle):
             formats.append(QVideoFrame.Format_RGB24)
         return formats

    def present(self, frame:QVideoFrame)->bool:
        if (self.surfaceFormat().pixelFormat() != frame.pixelFormat() or
            self.surfaceFormat().frameSize() != frame.size()):
                self.setError(QAbstractVideoSurface.IncorrectFormatError)
                self.stop()
                return False
        self.currentFrame = frame
        img = QImage(self.currentFrame.bits(),
            self.currentFrame.width(), self.currentFrame.height(), self.currentFrame.bytesPerLine(),
            QImage.Format_RGB888)
        self.draw_image.emit(img)
        return True

class mainwin(QMainWindow):
    def __init__(self, parent=None):
        super(mainwin, self).__init__(parent)
        self.initUI()
        self._grabber = frameGrabber(self)
        self._grabber.draw_image.connect(self.drawImage)
        self._cam = QCamera(QCamera.FrontFace)
        self._cam.setViewfinder(self._grabber)
        self._cam.start()

    def initUI(self):
        self._central = QWidget(self)
        grid = QGridLayout(self)
        self._lbl_img = QLabel("img_lbl")
        self._lbl_fps = QLabel("fps:")
        self._lbl_cps = QLabel("cps:")
        self._btn_start = QPushButton("start")
        grid.addWidget(self._lbl_img, 0,0)
        grid.addWidget(self._lbl_fps, 1,0)
        grid.addWidget(self._lbl_cps, 1,1)
        grid.addWidget(self._btn_start, 1,2)
        self.setCentralWidget(self._central)
        self._central.setLayout(grid)

    @pyqtSlot(QImage)
    def drawImage(self, img:QImage):
        px = QPixmap.fromImage(img)
        self._lbl_img.setPixmap(px)

app = QApplication([])
win = mainwin()
win.show()
app.exec_(