MF_DEVSOURCE_ATTRIBUTE_FRAMESERVER_SHARE_MODES attribute

Configures a camera device source represented by an instance of IMFMEdiaSource to be in either controlling mode or sharing mode.

Data type

UINT32

Get/set

To get this attribute, call IMFAttributes::GetUINT32.

To set this attribute, call IMFAttributes::SetUINT32.

Remarks

When this attribute is either not set or set to 0 value, the camera device source is configured in controlling mode. This is the default mode for camera sources. When in controlling mode, all camera operations are available and the application may change media types and/or extended camera controls.

Only one controlling mode instance of IMFMediaSource can be in an active state at a any time. An IMFMediaSource is not considered active after it has been created an initialized. The media source only becomes active after the stream has been started, with a call to IMFMediaSource::Start, or after a camera control value is set either by issuing of a camera control by calling IKsControl::KsProperty with the property set KSPROPERTYSETID_ExtendedCameraControl or by using the IMFExtendedCameraControl interface. For information on getting instance of IMFExtendedCameraControl, see IMFExtendedCameraController

Attempting to activate an IMFMediaSource when another controlling mode instance is already active will result in a sharing violation.

At any time there can be an arbitrary number of active sharing mode instances of IMFMediaSource and newly created sharing mode instances can be activated while a controlling mode instance is active. Sharing mode instances cannot change media types and must use the current media type in use, unless no other sharing mode or controlling mode instances are active. Sharing mode instances cannot change KSPROPERTYSETID_ExtendedCameraControl controls. Legacy camera controls such as PROPSETID_VIDCAP_CAMERACONTROL and PROPSETID_VIDCAP_VIDEOPROCAMP and OEM/IHV-specific controls can be changed by sharing mode instances.

To configure a camera source to be in Sharing mode, the attribute must be set at the time of IMFMediaSource creation.

Configure sharing mode using MFCreateDeviceSource

The following code example illustrates creating an instance in sharing mode using MFCreateDeviceSource.

HRESULT
SampleCreateSharedModeCamera(
    _In_z_ LPCWSTR cameraSymbolicName,
    _COM_Outptr_ IMFMediaSource** cameraSource
    )
{
    wil::com_ptr_nothrow<IMFAttributes>     initAttributes;

    RETURN_HR_IF_NULL (E_INVALIDARG, cameraSymbolicName);
    RETURN_HR_IF_NULL (E_POINTER, cameraSource);
    *cameraSource = nullptr;

    RETURN_IF_FAILED (MFCreateAttributes(&initAttributes, 3));
    RETURN_IF_FAILED (initAttributes->SetGUID(MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE, MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID));
    RETURN_IF_FAILED (initAttributes->SetString(MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_SYMBOLIC_LINK, cameraSymbolicName));
    RETURN_IF_FAILED (initAttributes->SetUINT32(MF_DEVSOURCE_ATTRIBUTE_FRAMESERVER_SHARE_MODE, 1));
    RETURN_IF_FAILED (MFCreateDeviceSource(initAttributes.get(), deviceSource));

    return S_OK;
}

Configure sharing mode using IMFActivate

The following example illustrates creating an IMFMediaSource instance using IMFActivate. Note that The IMFActivate object will internally cache a newly created IMFMediaSource from the call to ActivateObject. So if ActivateObject is called again before a call to DetachObject is made, the cached instance will be returned and any changes to the attributes will be ignored.

HRESULT
SampleCreateSharedModeCameraFromActivate(
    _In_ IMFActivate* activate,
    _COM_Outptr_ IMFMediaSource** cameraSource
    )
{
    RETURN_HR_IF_NULL (E_INVALIDARG, activate);
    RETURN_HR_IF_NULL (E_POINTER, cameraSource);
    *cameraSource = nullptr;

    RETURN_IF_FAILED (activate->SetUINT32(MF_DEVSOURCE_ATTRIBUTE_FRAMESERVER_SHARE_MODE, 1));
    RETURN_IF_FAILED (activate->ActivateObject(IID_PPV_ARGS(deviceSource)));

    return S_OK;
}

Configure sharing mode using IMFCaptureEngine

To activate the IMFMediaSource in sharing mode using IMFCaptureEngine, the IMFActivate passed in for the camera source must have the MF_DEVSOURCE_ATTRIBUTE_FRAMESERVER_SHARE_MODE attribute. As stated above, after IMFActivate::ActivateObject is called, DetachObject must be called for any attribute changes to be reflected in the activated object.

Configure sharing mode using MediaCapture

When accessing the camera using the MediaCapture class, set sharing mode using the MediaCaptureInitializationSettings.SharingMode property.

Requirements

See also

Alphabetical List of Media Foundation Attributes

Audio/Video Capture

Capture Device Attributes