c++ - QAbstractVideoSurface 示例

Question

我正在尝试使自己成为具有更多功能的 QML 相机项目，并提供 VideoOutput 的来源元素。比如这样:

VideoOutput{
    source:mycamera
}
MyCustomCamera{
    id:mycamera
}

in the document it says

If you are extending your own C++ classes to interoperate with VideoOutput, you can either provide a QObject based class with a mediaObject property that exposes a QMediaObject derived class that has a QVideoRendererControl available, or you can provide a QObject based class with a writable videoSurface property that can accept a QAbstractVideoSurface based class and can follow the correct protocol to deliver QVideoFrames to it.

我试过给我的对象一个私有(private)属性 mediaObject ，它是 QCamera 类型，但看起来 QCamera 没有 QVideoRenderControl(或者我的错不知道如何正确执行它)。

我需要达到我一开始展示的效果，无论如何欢迎。

或者，谁能给我一个简短的例子，说明“接受 blablabla 并遵循正确协议(protocol)的可写 videoSurace 属性”是什么意思？

Answer 1

我无法帮助您解决您的主要问题，但我可以为您提供 videoSurface 的示例用法.您可以像这样使用“可写videoSurface”:

我的示例包括三个主要步骤:

您编写了一个具有 QAbstactVideoSurface 属性的类。这个类将是你的视频提供者，它可以通过调用它的 present() 函数在 VideoOutput 上显示帧。

视频适配器.h

#ifndef VIDEOADAPTER_H
#define VIDEOADAPTER_H
#include <QObject>
#include <QAbstractVideoSurface>
#include <QVideoSurfaceFormat>
#include <QTimer>

class VideoAdapter : public QObject
{
  Q_OBJECT
  Q_PROPERTY(QAbstractVideoSurface* videoSurface READ videoSurface WRITE setVideoSurface NOTIFY signalVideoSurfaceChanged)
public:
  explicit VideoAdapter(QObject *parent = nullptr);

  QAbstractVideoSurface *videoSurface() const;
  void setVideoSurface(QAbstractVideoSurface *videoSurface);

signals:
  void signalVideoSurfaceChanged();

private slots:
  void slotTick();

private:
  void startSurface();

private:
  QAbstractVideoSurface *mVideoSurface;
  QVideoSurfaceFormat *mSurfaceFormat;
  QImage *mImage;
  QTimer mTimer;
};

#endif // VIDEOADAPTER_H

视频适配器.cpp

#include "videoadapter.h"
#include <QDebug>

VideoAdapter::VideoAdapter(QObject *parent)
  : QObject(parent), mVideoSurface(nullptr), mSurfaceFormat(nullptr)
{
  mTimer.setInterval(1000);
  connect(&mTimer, &QTimer::timeout, this, &VideoAdapter::slotTick);
}

QAbstractVideoSurface *VideoAdapter::videoSurface() const
{
  return mVideoSurface;
}

void VideoAdapter::setVideoSurface(QAbstractVideoSurface *videoSurface)
{
  if(videoSurface != mVideoSurface)
  {
    mVideoSurface = videoSurface;
    emit signalVideoSurfaceChanged();
    startSurface();

    // This is the test timer that will tick for us to present the image
    // on the video surface
    mTimer.start();
  }
}

void VideoAdapter::slotTick()
{
  QVideoFrame frame(*mImage);
  mVideoSurface->present(frame);
}

void VideoAdapter::startSurface()
{
  mImage = new QImage("../resources/images/test.jpg");
  auto pixelFormat = QVideoFrame::pixelFormatFromImageFormat(mImage->format());
  mSurfaceFormat = new QVideoSurfaceFormat(mImage->size(), pixelFormat);
  if(!mVideoSurface->start(*mSurfaceFormat))
  {
    qDebug() << "Surface couldn't be started!";
  }
}

此类仅加载图像文件并使用计时器显示它，但在您的情况下，您将拥有一个帧源，因此您可以更改它以满足您的需要。如果您可以将框架转换为 QImage的 QVideoFrame你可以像这样显示它。

您必须使此类在 QML 中可用。在我的情况下，我创建了一个对象并通过将其设置为属性使其对 QML 可见。

int main(int argc, char *argv[])
{
  QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

  QGuiApplication app(argc, argv);

  QQmlApplicationEngine engine;

  QQmlDebuggingEnabler enabler;

  VideoAdapter adapter;
  // When you do this this object is made visible to QML context with the
  // given name
  engine.rootContext()->setContextProperty("videoAdapter", &adapter);

  const QUrl url(QStringLiteral("qrc:/main.qml"));
  QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                   &app, [url](QObject *obj, const QUrl &objUrl) {
      if (!obj && url == objUrl)
          QCoreApplication::exit(-1);
  }, Qt::QueuedConnection);
  engine.load(url);

  return app.exec();
}

您将此对象作为 QML 中的源提供给 VideoOutput。

Window {
  visible: true
  width: 640
  height: 480
  color: "black"
  title: qsTr("Video Player")

  VideoOutput {
    id: videoPlayer
    anchors.fill: parent
    source: videoAdapter
  }
}

正如我所说的这个例子是一个简单的例子，它只加载一个图像并且只定期显示一个图像。

这个问题是一个老问题，你可能会继续前进，但希望这至少可以帮助其他人。