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相机示例

演示如何捕捉静态图像或录制视频。

相机示例演示如何使用 Qt Multimedia实现一些基本的相机功能，以拍摄静态图像和录制带音频的视频片段。

运行示例

运行示例 Qt Creator，打开Welcome 模式，然后从Examples 中选择示例。更多信息，请参阅Qt Creator: 教程：构建并运行。

该示例实现了一个Camera 类，作为我们的摄像机接口。该类具有用户界面、控制功能、设置值以及定义图像或视频片段保存位置的方法。它还将存储图像和视频设置。

相机类使用

  • QCamera 的实例，这是硬件的 API 类接口。
  • QImageCapture 的一个实例，用于拍摄静态图像。
  • QMediaRecorder 的一个实例，用于录制视频。它还包含用户界面对象。

相机构造函数

摄像机构造函数对用户界面进行一些基本的初始化，包括默认禁用所有按钮。

Camera::Camera() : ui(new Ui::Camera)
{
    ui->setupUi(this);
    // disable all buttons by default
    updateCameraActive(false);
    readyForCapture(false);
    ui->recordButton->setEnabled(false);
    ui->pauseButton->setEnabled(false);
    ui->stopButton->setEnabled(false);
    ui->metaDataButton->setEnabled(false);

它还会寻求输入设备访问权限：

#if QT_CONFIG(permissions) // 摄像头   QCameraPermissioncameraPermission;switch(qApp->checkPermission(cameraPermission)) {caseQt::PermissionStatus::Undetermined：        qApp->requestPermission(cameraPermission, this, &Camera::init);
       return;caseQt::PermissionStatus::Denied：        qWarning("Camera permission is not granted!");
       return;caseQt::PermissionStatus::Granted: break; }// microphone   QMicrophonePermissionmicrophonePermission;switch(qApp->checkPermission(microphonePermission)) {caseQt::PermissionStatus::Undetermined：        qApp->requestPermission(microphonePermission, this, &Camera::init);
       return;caseQt::PermissionStatus::Denied：        qWarning("Microphone permission is not granted!");
       return;caseQt::PermissionStatus::Granted:break; }#endif

输入已分配：

    m_audioInput.reset(new QAudioInput);
    m_captureSession.setAudioInput(m_audioInput.get());

    // Camera devices:

    videoDevicesGroup = new QActionGroup(this);
    videoDevicesGroup->setExclusive(true);
    updateCameras();

UI 信号连接到对触发事件做出反应的插槽：

    connect(&m_devices, &QMediaDevices::videoInputsChanged, this, &Camera::updateCameras);

    connect(videoDevicesGroup, &QActionGroup::triggered, this, &Camera::updateCameraDevice);
    connect(ui->captureWidget, &QTabWidget::currentChanged, this, &Camera::updateCaptureMode);

    connect(ui->metaDataButton, &QPushButton::clicked, this, &Camera::showMetaDataDialog);
    connect(ui->exposureCompensation, &QAbstractSlider::valueChanged, this,
            &Camera::setExposureCompensation);

    setCamera(QMediaDevices::defaultVideoInput());

不过，大部分工作都是在调用setCamera()函数时完成的，该函数会传入一个QCameraDevice 。

setCamera()

setCamera() 使用信号和槽在用户界面和相机类功能之间建立各种连接。它还会实例化和初始化 、 和 对象。QCamera QImageCapture QMediaRecorder 

void Camera::setCamera(const QCameraDevice &cameraDevice)
{
    m_camera.reset(new QCamera(cameraDevice));
    m_captureSession.setCamera(m_camera.data());

    connect(m_camera.data(), &QCamera::activeChanged, this, &Camera::updateCameraActive);
    connect(m_camera.data(), &QCamera::errorOccurred, this, &Camera::displayCameraError);

    if (!m_mediaRecorder) {
        m_mediaRecorder.reset(new QMediaRecorder);
        m_captureSession.setRecorder(m_mediaRecorder.data());
        connect(m_mediaRecorder.data(), &QMediaRecorder::recorderStateChanged, this,
                &Camera::updateRecorderState);
        connect(m_mediaRecorder.data(), &QMediaRecorder::durationChanged, this,
                &Camera::updateRecordTime);
        connect(m_mediaRecorder.data(), &QMediaRecorder::errorChanged, this,
                &Camera::displayRecorderError);
    }

    if (!m_imageCapture) {
        m_imageCapture.reset(new QImageCapture);
        m_captureSession.setImageCapture(m_imageCapture.get());
        connect(m_imageCapture.get(), &QImageCapture::readyForCaptureChanged, this,
                &Camera::readyForCapture);
        connect(m_imageCapture.get(), &QImageCapture::imageCaptured, this,
                &Camera::processCapturedImage);
        connect(m_imageCapture.get(), &QImageCapture::imageSaved, this, &Camera::imageSaved);
        connect(m_imageCapture.get(), &QImageCapture::errorOccurred, this,
                &Camera::displayCaptureError);
    }

静态和视频录制可视化选项卡已启用：

    m_captureSession.setVideoOutput(ui->viewfinder);

    updateCameraActive(m_camera->isActive());
    updateRecorderState(m_mediaRecorder->recorderState());
    readyForCapture(m_imageCapture->isReadyForCapture());

    updateCaptureMode();

最后调用QCamera 对象的start() 函数。

    m_camera->start();

触发捕获

现在，摄像机已准备好接受用户指令，它正在等待一个合适的事件。这种事件可以是按下应用程序窗口上的Qt::Key_CameraFocus 或Qt::Key_Camera 按钮。

按键_CameraFocus 只需显示预览并锁定摄像机设置。

}

void Camera::keyPressEvent(QKeyEvent *event)
{
    if (event->isAutoRepeat())
        return;

    switch (event->key()) {
    case Qt::Key_CameraFocus:
        displayViewfinder();
        event->accept();
        break;

Key_Camera 在录制视频时，如果进行图像捕捉，将调用takeImage()；如果已在录制，则调用 实例上的 或 （如果已在录制）。QMediaRecorder record() stop() 

    case Qt::Key_Camera:
        if (m_doImageCapture) {
            takeImage();
        } else {
            if (m_mediaRecorder->recorderState() == QMediaRecorder::RecordingState)
                stop();
            else
                record();
        }
        event->accept();
        break;

示例项目 @ code.qt.io

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