IAudioEffectsChangedNotificationClient::OnAudioEffectsChanged method (audioclient.h)

Article
05/22/2024

Called by the system when the list of audio effects changes or the resources needed to enable an effect changes, i.e. when the value of the canSetState field of the associated AUDIO_EFFECT changes.

Syntax

HRESULT OnAudioEffectsChanged();

Return value

An HRESULT.

Remarks

Example

The following code example demonstrates a class that implements IAudioEffectsChangedNotificationClient to receive notifications when the list of audio effects changes or the resources needed to enable an effect changes. In the OnAudioStreamEffectsChanged callback, the example calls GetAudioEffects to get the current list of effects.

class AudioEffectsChangedHandler :
    public winrt::implements<AudioEffectsChangedHandler, IAudioEffectsChangedNotificationClient>
{

    public:
    AudioEffectsChangedHandler(_In_ IAudioClient *client) : m_client(client){}
    STDMETHOD(OnAudioEffectsChanged)()
    {
        OnAudioStreamEffectsChanged(m_client.get());
        return S_OK;
    }
    private:
    wil::com_ptr_nothrow<IAudioClient> m_client;

};

wil::com_ptr_nothrow<IAudioEffectsChangedNotificationClient> g_effectsChangedHandler;

HRESULT RegisterAudioStreamEffectsChangedEvent(_In_ IAudioClient *client)
{
    if (!g_effectsChangedHandler)
    {
        wil::com_ptr_nothrow<IAudioEffectsManager> audioEffectsManager;
        RETURN_IF_FAILED(client->GetService(IID_PPV_ARGS(&audioEffectsManager)));

        // Register for the audio effects changed notification
        g_effectsChangedHandler = winrt::make<AudioEffectsChangedHandler>(client).get();
        RETURN_IF_NULL_ALLOC(g_effectsChangedHandler);

        return audioEffectsManager->RegisterAudioEffectsChangedNotificationCallback(
            g_effectsChangedHandler.get());
    }
    return S_OK;
}

HRESULT UnregisterAudioStreamEffectsChangedEvent(_In_ IAudioClient *client)
{
    if (g_effectsChangedHandler != nullptr)
    {
        wil::com_ptr_nothrow<IAudioEffectsManager> audioEffectsManager;
        RETURN_IF_FAILED(client->GetService(IID_PPV_ARGS(&audioEffectsManager)));

        // Unregister from the audio effects changed notification 
        return audioEffectsManager->UnregisterAudioEffectsChangedNotificationCallback(
            g_effectsChangedHandler.get());
        }

        return S_OK;
}

HRESULT OnAudioStreamEffectsChanged(_In_ IAudioClient *client)
{
    // Re-query the list of effects since there was some change
    wil::com_ptr_nothrow<IAudioEffectsManager> audioEffectsManager;
    RETURN_IF_FAILED(client->GetService(IID_PPV_ARGS(&audioEffectsManager)));
    wil::unique_cotaskmem_array_ptr<AUDIO_EFFECT> effects;
    UINT32 numEffects;
    RETURN_IF_FAILED(audioEffectsManager->GetAudioEffects(&effects, &numEffects));

    for (UINT32 i = 0; i < numEffects; i++)
    {

        // Here the app can check which effects are still enabled, and check if there are new
        // effects that now can be enabled.
        // As an example, the following code enables any effect that can be enabled, if it is not
        // already enabled.
        if (effects[i].canSetState && effects[i].state == AUDIO_EFFECT_STATE_OFF)
        {
            HRESULT hr = audioEffectsManager->SetAudioEffectState(effects[i].id, AUDIO_EFFECT_STATE_ON));
            if (hr == AUDCLNT_E_EFFECT_NOT_AVAILABLE || hr == AUDCLNT_E_EFFECT_STATE_READ_ONLY)
            {
                hr = S_OK;
            }
            RETURN_IF_FAILED(hr);

        }
    }

    return S_OK;
}

Requirements

Requirement	Value
Minimum supported client	Windows Build 22000
Header	audioclient.h

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