macOS: enable to set FPS for QCamera

qDebug() << "Except"
<< "max rate = " << kExceptSetting.maximumFrameRate()
<< "min rate = " << kExceptSetting.minimumFrameRate()
<< "resolution = " << kExceptSetting.resolution()
<< "Format =" << kExceptSetting.pixelFormat()
<< "" << kExceptSetting.pixelAspectRatio();

qDebug() << "Before"
<< "max rate = " << m_pCamera->viewfinderSettings().maximumFrameRate()
<< "min rate = " << m_pCamera->viewfinderSettings().minimumFrameRate()
<< "resolution = " << m_pCamera->viewfinderSettings().resolution()
<< "Format =" << m_pCamera->viewfinderSettings().pixelFormat()
<< "" << m_pCamera->viewfinderSettings().pixelAspectRatio();

m_pCamera->setViewfinderSettings( kExceptSetting );
qDebug() << "After"
<< "max rate = " << m_pCamera->viewfinderSettings().maximumFrameRate()
<< "min rate = " << m_pCamera->viewfinderSettings().minimumFrameRate()
<< "resolution = " << m_pCamera->viewfinderSettings().resolution()
<< "Format =" << m_pCamera->viewfinderSettings().pixelFormat()
<< "" << m_pCamera->viewfinderSettings().pixelAspectRatio();
m_pCamera->start();
}
}

void Camera::onStateChanged( QCamera::State eState )
{
if ( eState == QCamera::ActiveState )
{
qDebug() << "Final"
<< "max rate = " << m_pCamera->viewfinderSettings().maximumFrameRate()
<< "min rate = " << m_pCamera->viewfinderSettings().minimumFrameRate()
<< "resolution = " << m_pCamera->viewfinderSettings().resolution()
<< "Format =" << m_pCamera->viewfinderSettings().pixelFormat()
<< "" << m_pCamera->viewfinderSettings().pixelAspectRatio();
}
}

The content of "Except" is : max rate = 5 min rate = 5 resolution = QSize (640, 480) Format = Format_ARGB32 QSize (1, 1)
The content of "Before" is : max rate = 20 min rate = 20 resolution = QSize (1280, 1024) Format = Format_UYVY QSize (1, 1)
The content of "After" is : max rate = 5 min rate = 5 resolution = QSize (640, 480) Format = Format_ARGB32 QSize (1, 1)
The content of "Final" is : max rate = 27.5 min rate = 27.5 resolution = QSize (1280, 1024) Format = Format_ARGB32 QSize (1, 1)