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Supporting Rendering Profiles

Last Updated: 1/24/2017

An 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 how an application retrieves a rendering profile, see the Retrieving the Rendering Capabilities Supported by a Device topic in the WPD SDK.

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

When an application requests a rendering profile, 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, the receipt of this command 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;
}

The SetRenderingProfiles 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;
}

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