PyQt5 抓取当前帧显示空白

PyQt5 grabbing current frame displays blank

我是 PyQt 的新手,我正在尝试创建一个视频播放器来截取它检索到的当前帧。我实现了 method for grabbing the videoframes in order to take screenshots and added it to a videoplayer GUI。以下是 GUI 的基本外观:

我使用以下代码在 VideoWindow class 中为屏幕截图操作创建了一个触发器:

screenshotAction = QAction(QIcon('screenshot.png'), '&Screenshot', self)
screenshotAction.setShortcut('Ctrl+S')
screenshotAction.setStatusTip('Screenshot scenes')
screenshotAction.triggered.connect(self.screenshotCall)

然后我实现了并在截图函数中调用它:

def screenshotCall(self):
        #Call video frame grabber
        self.grabber = VideoFrameGrabber(self.videoWidget, self)
        self.mediaPlayer.setVideoOutput(self.grabber)
        self.grabber.frameAvailable.connect(self.process_frame)
        self.mediaPlayer.setVideoOutput(self.videoWidget)

完整代码:

# PyQt5 Video player
#!/usr/bin/env python

from PyQt5.QtCore import QDir, Qt, QUrl, pyqtSignal, QPoint, QRect, QObject
from PyQt5.QtMultimedia import QMediaContent, QMediaPlayer, QVideoFrame, QAbstractVideoSurface, QAbstractVideoBuffer, QVideoSurfaceFormat
from PyQt5.QtMultimediaWidgets import QVideoWidget
from PyQt5.QtWidgets import (QApplication, QFileDialog, QHBoxLayout, QLabel,
        QPushButton, QSizePolicy, QSlider, QStyle, QVBoxLayout, QWidget)
from PyQt5.QtWidgets import QMainWindow,QWidget, QPushButton, QAction
from PyQt5.QtGui import QIcon, QPainter, QImage
import sys
import os
import os.path as osp

class VideoFrameGrabber(QAbstractVideoSurface):
    frameAvailable = pyqtSignal(QImage)

    def __init__(self, widget: QWidget, parent: QObject):
        super().__init__(parent)

        self.widget = widget
    def supportedPixelFormats(self, handleType):
        return [QVideoFrame.Format_ARGB32, QVideoFrame.Format_ARGB32_Premultiplied,
                QVideoFrame.Format_RGB32, QVideoFrame.Format_RGB24, QVideoFrame.Format_RGB565,
                QVideoFrame.Format_RGB555, QVideoFrame.Format_ARGB8565_Premultiplied,
                QVideoFrame.Format_BGRA32, QVideoFrame.Format_BGRA32_Premultiplied, QVideoFrame.Format_BGR32,
                QVideoFrame.Format_BGR24, QVideoFrame.Format_BGR565, QVideoFrame.Format_BGR555,
                QVideoFrame.Format_BGRA5658_Premultiplied, QVideoFrame.Format_AYUV444,
                QVideoFrame.Format_AYUV444_Premultiplied, QVideoFrame.Format_YUV444,
                QVideoFrame.Format_YUV420P, QVideoFrame.Format_YV12, QVideoFrame.Format_UYVY,
                QVideoFrame.Format_YUYV, QVideoFrame.Format_NV12, QVideoFrame.Format_NV21,
                QVideoFrame.Format_IMC1, QVideoFrame.Format_IMC2, QVideoFrame.Format_IMC3,
                QVideoFrame.Format_IMC4, QVideoFrame.Format_Y8, QVideoFrame.Format_Y16,
                QVideoFrame.Format_Jpeg, QVideoFrame.Format_CameraRaw, QVideoFrame.Format_AdobeDng]

    def isFormatSupported(self, format):
        imageFormat = QVideoFrame.imageFormatFromPixelFormat(format.pixelFormat())
        size = format.frameSize()

        return imageFormat != QImage.Format_Invalid and not size.isEmpty() and \
               format.handleType() == QAbstractVideoBuffer.NoHandle

    def start(self, format: QVideoSurfaceFormat):
        imageFormat = QVideoFrame.imageFormatFromPixelFormat(format.pixelFormat())
        size = format.frameSize()

        if imageFormat != QImage.Format_Invalid and not size.isEmpty():
            self.imageFormat = imageFormat
            self.imageSize = size
            self.sourceRect = format.viewport()

            super().start(format)

            self.widget.updateGeometry()
            self.updateVideoRect()

            return True
        else:
            return False

    def stop(self):
        self.currentFrame = QVideoFrame()
        self.targetRect = QRect()

        super().stop()

        self.widget.update()

    def present(self, frame):
        if frame.isValid():
            cloneFrame = QVideoFrame(frame)
            cloneFrame.map(QAbstractVideoBuffer.ReadOnly)
            image = QImage(cloneFrame.bits(), cloneFrame.width(), cloneFrame.height(),
                           QVideoFrame.imageFormatFromPixelFormat(cloneFrame.pixelFormat()))
            self.frameAvailable.emit(image)  # this is very important
            cloneFrame.unmap()

        if self.surfaceFormat().pixelFormat() != frame.pixelFormat() or \
                self.surfaceFormat().frameSize() != frame.size():
            self.setError(QAbstractVideoSurface.IncorrectFormatError)
            self.stop()

            return False
        else:
            self.currentFrame = frame
            self.widget.repaint(self.targetRect)

            return True

    def updateVideoRect(self):
        size = self.surfaceFormat().sizeHint()
        size.scale(self.widget.size().boundedTo(size), Qt.KeepAspectRatio)

        self.targetRect = QRect(QPoint(0, 0), size)
        self.targetRect.moveCenter(self.widget.rect().center())

    def paint(self, painter):
        if self.currentFrame.map(QAbstractVideoBuffer.ReadOnly):
            oldTransform = self.painter.transform()

        if self.surfaceFormat().scanLineDirection() == QVideoSurfaceFormat.BottomToTop:
            self.painter.scale(1, -1)
            self.painter.translate(0, -self.widget.height())

        image = QImage(self.currentFrame.bits(), self.currentFrame.width(), self.currentFrame.height(),
                       self.currentFrame.bytesPerLine(), self.imageFormat)

        self.painter.drawImage(self.targetRect, image, self.sourceRect)

        self.painter.setTransform(oldTransform)

        self.currentFrame.unmap()

class VideoWindow(QMainWindow):

    def __init__(self, parent=None):
        super(VideoWindow, self).__init__(parent)
        self.setWindowTitle("PyQt Video Player Widget") 

        self.counter = 0
        self.mediaPlayer = QMediaPlayer(None, QMediaPlayer.VideoSurface)
        self.videoWidget = QVideoWidget()
        self.videoFrame = QVideoFrame()
        self.playButton = QPushButton()
        self.playButton.setEnabled(False)
        self.playButton.setIcon(self.style().standardIcon(QStyle.SP_MediaPlay))
        self.playButton.clicked.connect(self.play)

        self.positionSlider = QSlider(Qt.Horizontal)
        self.positionSlider.setRange(0, 0)
        self.positionSlider.sliderMoved.connect(self.setPosition)

        self.errorLabel = QLabel()
        self.errorLabel.setSizePolicy(QSizePolicy.Preferred,
                QSizePolicy.Maximum)
        # Create new action
        openAction = QAction(QIcon('open.png'), '&Open', self)        
        openAction.setShortcut('Ctrl+O')
        openAction.setStatusTip('Open video')
        openAction.triggered.connect(self.openFile)

        # Create exit action
        exitAction = QAction(QIcon('quit.png'), '&Exit', self)        
        exitAction.setShortcut('Ctrl+Q')
        exitAction.setStatusTip('Exit application')
        exitAction.triggered.connect(self.exitCall)

        screenshotAction = QAction(QIcon('screenshot.png'), '&Screenshot', self)
        screenshotAction.setShortcut('Ctrl+S')
        screenshotAction.setStatusTip('Screenshot scenes')
        screenshotAction.triggered.connect(self.screenshotCall)

        # Create menu bar and add action
        menuBar = self.menuBar()
        fileMenu = menuBar.addMenu('&File')
        #fileMenu.addAction(newAction)
        fileMenu.addAction(openAction)
        fileMenu.addAction(screenshotAction)
        fileMenu.addAction(exitAction)


        # Create a widget for window contents
        wid = QWidget(self)
        self.setCentralWidget(wid)

        # Create layouts to place inside widget
        controlLayout = QHBoxLayout()
        controlLayout.setContentsMargins(0, 0, 0, 0)
        controlLayout.addWidget(self.playButton)
        controlLayout.addWidget(self.positionSlider)

        layout = QVBoxLayout()
        layout.addWidget(self.videoWidget)
        layout.addLayout(controlLayout)
        layout.addWidget(self.errorLabel)

        # Set widget to contain window contents
        wid.setLayout(layout)


        self.mediaPlayer.setVideoOutput(self.videoWidget)
        self.mediaPlayer.stateChanged.connect(self.mediaStateChanged)
        self.mediaPlayer.positionChanged.connect(self.positionChanged)
        self.mediaPlayer.durationChanged.connect(self.durationChanged)
        self.mediaPlayer.error.connect(self.handleError)

    def openFile(self):
        fileName, _ = QFileDialog.getOpenFileName(self, "Open Movie",
                QDir.homePath())
        self.path = osp.dirname(str(fileName))
        if fileName != '':
            self.mediaPlayer.setMedia(
                    QMediaContent(QUrl.fromLocalFile(fileName)))
            self.playButton.setEnabled(True)

    def exitCall(self):
        sys.exit(app.exec_())

    def screenshotCall(self):
        #Call video frame grabber
        self.grabber = VideoFrameGrabber(self.videoWidget, self)
        self.mediaPlayer.setVideoOutput(self.grabber)
        self.mediaPlayer.pause()
        self.grabber.frameAvailable.connect(self.process_frame)
        self.errorLabel.setText("Taking a screenshot of image "+str(self.counter)+" ....")
        self.mediaPlayer.play()
        self.mediaPlayer.setVideoOutput(self.videoWidget)

    def play(self):
        if self.mediaPlayer.state() == QMediaPlayer.PlayingState:
            self.mediaPlayer.pause()
        else:
            self.mediaPlayer.play()

    def mediaStateChanged(self, state):
        if self.mediaPlayer.state() == QMediaPlayer.PlayingState:
            self.playButton.setIcon(
                    self.style().standardIcon(QStyle.SP_MediaPause))
        else:
            self.playButton.setIcon(
                    self.style().standardIcon(QStyle.SP_MediaPlay))

    def positionChanged(self, position):
        self.positionSlider.setValue(position)

    def durationChanged(self, duration):
        self.positionSlider.setRange(0, duration)

    def setPosition(self, position):
        self.mediaPlayer.setPosition(position)

    def handleError(self):
        self.playButton.setEnabled(False)
        self.errorLabel.setText("Error: " + self.mediaPlayer.errorString())

    def process_frame(self, image):
        # Save image here
        filename = "screenshot" + str(self.counter).zfill(6)
        self.path = 'C:/Desktop/temp'
        image.save(self.path+'/{}.png'.format(str(filename)))
        self.counter = self.counter+1

if __name__ == '__main__':
    app = QApplication(sys.argv)
    player = VideoWindow()
    player.resize(720, 480)
    player.show()
    sys.exit(app.exec_())

但是,每当我尝试截取屏幕截图时,视频显示都会变黑。根据音频,视频仍在播放,但从截取屏幕截图的那一刻起,当前显示在整个视频持续时间内一直保持黑色。当播放器暂停和仍在播放时都会发生这种情况。我认为这是因为行 self.mediaPlayer.setVideoOutput(self.grabber),因为它用抓取器覆盖了屏幕上的当前显示。

我试过调用 videoWidget 并将其设置为抓取帧后的视频输出,但它似乎覆盖了抓取器并且根本不产生任何屏幕截图。

有没有办法让我在截屏的同时还在 GUI 上显示视频?

通过在每次播放视频时调用暂停函数解决此问题,然后在按下播放按钮时播放视频暂停的部分。

代码如下:

def screenshotCall(self):
        #Call video frame grabber
        self.grabber = VideoFrameGrabber(self.videoWidget, self)
        self.mediaPlayer.setVideoOutput(self.grabber)
        self.grabber.frameAvailable.connect(self.process_frame)
        self.errorLabel.setText("Taking a screenshot of image "+str(self.counter)+" ....")
        self.mediaPlayer.pause()

def play(self):
    if self.mediaPlayer.state() == QMediaPlayer.PlayingState:
        self.mediaPlayer.pause()
    else:
        self.mediaPlayer.play()
        self.mediaPlayer.setVideoOutput(self.videoWidget)