A given audio or video device may support specific rendering profiles. For example, an audio streaming device may stream a particular type of content at a specific bitrate over multiple channels. The content type, streaming bitrate, and channel count are referred to as a rendering profile.

WPD applications will often retrieve a rendering profile from the driver. For more information about the application-side of rendering profile retrieval, see the Windows Portable Devices Programming Guide in the WPD SDK.

This topic describes how the WpdWudfSampleDriver implements support for audio streaming in the helpers.cpp module.

When an application issues a request for rendering profiles, the driver receives a WPD_COMMAND_OBJECT_PROPERTIES_GET command with a command category of WPD_CATEGORY_OBJECT_PROPERTIES and a WPD_PROPERTY_OBJECT_PROPERTIES_OBJECT_ID of RenderingInformation. In the sample driver, this triggers a call to the SetRenderingProfile function in the helpers.cpp module.

HRESULT SetRenderingProfiles(
    IPortableDeviceValues*          pValues)
{
    HRESULT hr = S_OK;
    CComPtr<IPortableDeviceValues> pPreferredProfile;
    CComPtr<IPortableDeviceValues> pProfile2;

    CComPtr<IPortableDeviceValuesCollection> pProfiles;

    if(pValues == NULL)
    {
        hr = E_POINTER;
        CHECK_HR(hr, ("Cannot have NULL parameter"));
        return hr;
    }

    // Create the collection to hold the profiles
    if (hr == S_OK)
    {
        hr = CoCreateInstance(CLSID_PortableDeviceValuesCollection,
                              NULL,
                              CLSCTX_INPROC_SERVER,
                              IID_IPortableDeviceValuesCollection,
                              (VOID**) &pProfiles;);
        CHECK_HR(hr, "Failed to CoCreateInstance CLSID_PortableDeviceValuesCollection");
    }

    // Get the preferred audio profile
    if (hr == S_OK)
    {
        hr = GetPreferredAudioProfile(&pPreferredProfile;);
        CHECK_HR(hr, "Failed to get preferred audio profile properties");
    }

    // Add the profile
    if (hr == S_OK)
    {
        hr = pProfiles->Add(pPreferredProfile);
        CHECK_HR(hr, "Failed to add preferred audio profile to profile collection");
    }

    // Get the second audio profile
    if (hr == S_OK)
    {
        hr = GetAudioProfile2(&pProfile2;);
        CHECK_HR(hr, "Failed to get second audio profile properties");
    }

    // Add the profile
    if (hr == S_OK)
    {
        hr = pProfiles->Add(pProfile2);
        CHECK_HR(hr, "Failed to add second audio profile to profile collection");
    }

    // Set the WPD_RENDERING_INFORMATION_PROFILES
    if (hr == S_OK)
    {
        hr = pValues->SetIPortableDeviceValuesCollectionValue(WPD_RENDERING_INFORMATION_PROFILES, pProfiles);
        CHECK_HR(hr, "Failed to set WPD_RENDERING_INFORMATION_PROFILES");
    }

    return hr;
}

This function, in turn, calls the GetPreferredAudioProfile helper function which returns the actual profile information in an IPortableDeviceValues object.

HRESULT GetPreferredAudioProfile(
    IPortableDeviceValues** ppProfile)
{
    HRESULT hr = S_OK;
    CComPtr<IPortableDeviceValues> pProfile;

    if(ppProfile == NULL)
    {
        hr = E_POINTER;
        CHECK_HR(hr, ("Cannot have NULL parameter"));
        return hr;
    }

    if (hr == S_OK)
    {
        hr = CoCreateInstance(CLSID_PortableDeviceValues,
                              NULL,
                              CLSCTX_INPROC_SERVER,
                              IID_IPortableDeviceValues,
                              (VOID**) &pProfile;);
        CHECK_HR(hr, "Failed to CoCreateInstance CLSID_PortableDeviceValues");
    }

    // Set the value for WPD_OBJECT_FORMAT to indicate this profile applies to WMA objects
    if (hr == S_OK)
    {
        hr = pProfile->SetGuidValue(WPD_OBJECT_FORMAT, WPD_OBJECT_FORMAT_WMA);
        CHECK_HR(hr, "Failed to set WPD_OBJECT_FORMAT");
    }

    // Set the preferred value for WPD_MEDIA_TOTAL_BITRATE
    if (hr == S_OK)
    {
        hr = pProfile->SetUnsignedIntegerValue(WPD_MEDIA_TOTAL_BITRATE, 192000);
        CHECK_HR(hr, "Failed to set WPD_MEDIA_TOTAL_BITRATE");
    }

    // Set the preferred value for WPD_AUDIO_CHANNEL_COUNT
    if (hr == S_OK)
    {
        hr = pProfile->SetUnsignedIntegerValue(WPD_AUDIO_CHANNEL_COUNT, 2);
        CHECK_HR(hr, "Failed to set WPD_AUDIO_CHANNEL_COUNT");
    }

    // Set the preferred value for WPD_AUDIO_FORMAT_CODE
    if (hr == S_OK)
    {
        hr = pProfile->SetUnsignedIntegerValue(WPD_AUDIO_FORMAT_CODE, WAVE_FORMAT_MSAUDIO3);
        CHECK_HR(hr, "Failed to set WPD_AUDIO_FORMAT_CODE");
    }

    // Set the output result
    if (hr == S_OK)
    {
        hr = pProfile->QueryInterface(IID_PPV_ARGS(ppProfile));
        CHECK_HR(hr, "Failed to QI for IPortableDeviceValues");
    }

    return hr;
}