pyqt5中qabstractvideosurface的present()视频帧错误

Question

我正在研究一个带有 pyqt5 的应用程序。我使用 QMediaPlayer 和 QVideoWidget 播放视频，我首先需要做的是在暂停视频时获取当前视频帧。我已经阅读了答案，我已经实现了 QAbstractVideoSurface 并覆盖了那些方法。最后我能够获取视频帧，QAbstractVideoSurface 代码如下所示：

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

    def __init__(self, widget: QWidget, parent=None):
        super().__init__(parent)
        self.widget = widget
        self.current_frame = None
        self.image_format = QImage.Format_Invalid
        self.target_rect = None
        self.source_rect = None
        self.image_size = None

    def supportedPixelFormats(self, type):
        print("supportedPixelFormats() called")
        print("supportedPixelFormats() finished")
        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):
        print("isFormatSupported() called")

        image_format = QVideoFrame.imageFormatFromPixelFormat(format.pixelFormat())
        size = format.frameSize()

        print("isFormatSupported() finished")
        return image_format != QVideoFrame.Format_Invalid and not size.isEmpty() and \
            format.handleType() == QAbstractVideoBuffer.NoHandle

    def start(self, format):
        print("start() called")

        image_format = QVideoFrame.imageFormatFromPixelFormat(format.pixelFormat())
        size = format.frameSize()

        if image_format != QImage.Format_Invalid and not size.isEmpty():
            self.image_format = image_format
            self.image_size = size
            self.source_rect = format.viewport()

            super().start(format)                      
            # self.widget.updateGeometry()
            # self.update_video_rect()

            print("start() finished")
            return True
        else:
            print("start() finished")
            return False

    def stop(self):
        print("stop() called")

        self.current_frame = QVideoFrame()
        self.target_rect = QRect()

        super().stop()                                

        print("stop() finished")

    def present(self, frame: QVideoFrame):
        print("present called")

        if frame.isValid():

            clone_frame = QVideoFrame(frame)

            clone_frame.map(QAbstractVideoBuffer.ReadOnly)
            image = QImage(clone_frame.bits(), frame.width(), frame.height(), frame.bytesPerLine(), \
                QVideoFrame.imageFormatFromPixelFormat(frame.pixelFormat()))
            clone_frame.unmap()

            # image.save("frame.jpg")
            self.frame_available.emit(image)         

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

            print("present finished: Return False")
            return False
        else:
            self.current_frame = frame
            # self.widget.repaint(self.target_rect)

            print("present finished: Return True")
            return True

    def update_video_rect(self):
        print("update_video_rect() called")

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

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

        print("update_video_rect() finished")

    def paint(self, painter):
        print("paint() called")
        if self.current_frame.map(QAbstractVideoBuffer.ReadOnly):
            old_transform = painter.transform()

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

            image = QImage(self.current_frame.bits(), self.current_frame.width(), self.current_frame.height(),
                        self.current_frame.bytesPerLine(), self.image_format)
            self.painter.drawImage(self.target_rect, image, self.source_rect)
            self.painter.setTransform(old_transform)
            self.current_frame.unmap()

        print("paint() finished")

并且因为我使用 QVideoWidget 来播放视频，所以我需要将 QMediaPlayer 的输出更改为我的 QAbstractVideoSurface 以获得这样的视频帧。

# definition here
class PlayerMainWindow(Ui_MainWindow, QMainWindow):
    def __init__(self, parent=None):
        self.player = QMediaPlayer(self)
        self.player.setVideoOutput(self.video_widget)
        self.auto_video_grabber = VideoFrameGrabber(self)
        # what I need to do next is to detect faces in the frame
        self.auto_video_grabber.frame_available.connect(self.auto_detect)

    def auto_detect_clicked(self):
        # the detector_widget is a widget contains serveral labels to show process information 
        # use signal and slot to update those lables 
        if self.detector_widget.is_detecting():
            return

        self.detector_widget.connect_face_available(self.on_face_available)
        self.stackedWidget.setCurrentIndex(1)    # the detector widget

        self.player.setVideoOutput(self.auto_video_grabber)
        self.player.pause()

    # Receive frame(QImage) in auto_detect()
    def auto_detect(self, frame: QImage):
        
        self.player.setVideoOutput(self.video_widget)
        self.player.pause()

        if frame is None:
            return

        frame.save("auto_capture.jpg")
        
        self.detector_widget.start_detector(frame)

但现在的问题是，有时我在auto_detect()中获得的帧不是我暂停视频时的当前帧（该帧已播放）但有时它是正确的。我也尝试用 present() 方法保存帧，但它与我在 auto_detect() 方法中收到的相同。

Answer 1

天呐，终于解决问题了。上面显示的代码没问题，我所做的是将视频解码器从 LAV 更改为 K-Lite.

pyqt5中qabstractvideosurface的present()视频帧错误

wrong video frame of present() of qabstractvideosurface in pyqt5

python

pyqt

qmediaplayer

pyqt5

qvideowidget