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相机示例

演示如何拍摄静态图像或录制视频。

带图像和视频拍摄控制功能的相机应用程序界面

“相机示例”演示了如何使用 Qt Multimedia 来实现一些基本的相机功能，用于拍摄静态图像和录制带音频的视频片段。

运行示例

您可以从以下位置运行该示例：

该示例实现了一个Camera 类，用作我们的相机接口。它包含用户界面、控制功能、设置选项，以及定义图像或视频片段保存位置的功能。它还会保存图像和视频的设置。

Camera 类使用：

  • QCamera 的实例，即与硬件交互的 API 类接口。
  • QImageCapture 的实例，用于拍摄静态图像。
  • QMediaRecorder 的实例，用于录制视频。它还包含用户界面对象。

Camera 构造函数

Camera 构造函数会对用户界面进行一些基本初始化，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);

它会请求访问输入设备的权限：

#if QT_CONFIG(permissions)
    // 摄像头
    QCameraPermission cameraPermission;
    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;
    }
    // 麦克风
    QMicrophonePermission 麦克风权限;
    switch(qApp->checkPermission(麦克风权限)) {
    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

已分配输入：

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

    // Camera devices:

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

UI 信号已连接到会响应触发事件的槽：

    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);

    setCamera(QMediaDevices::defaultVideoInput());

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

setCamera()

setCamera() 通过信号和槽，在用户界面与 Camera 类的功能之间建立各种连接。它还会实例化并初始化QCamera 、QImageCapture 和QMediaRecorder 对象。

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

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

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

静态照片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，调用了QCamera 对象的start()函数。

    m_camera->start();

触发捕获

现在，相机已准备好响应用户命令，正在等待合适的事件。此类事件可以是应用程序窗口上Qt::Key_CameraFocus 或Qt::Key_Camera 按钮的按键操作。

Key_CameraFocus 仅会显示预览并锁定相机设置。

}

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

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

Key_Camera 若进行图像捕获，则调用takeImage()；若正在录制视频，则调用QMediaRecorder 实例上的record() 或stop() （如果已经开始录制）。

    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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