Problems using Windows Core Audio

See more:

C++

C#

Windows

WPF

C#4.0

audio

Hello everyone,

I'm running into some serious problems using the Windows Core Audio API.
This question is, as I think, quite specific and maybe much too long for a quick question. Kindly let me know whether the discussion boards are a better place for this.
I also tagged this question with C++ because these are native APIs.

Just in short what I'd like to achieve:
I have a media player. Changing its volume shall be reflected in the Windows sound mixer and vice versa. I'm changing the session volume, not the master volume.

It's working with one little, annoying exception. When I'm dragging the slider within Windows' sound mixer it starts setting the volume like crazy. I've recorded a video and uploaded it to YouTube so that you can see what I'm talking about. You may find it here - click[^]. On the left side you see the sound mixer of Windows, on the right my media player.

Before I post the code, some remarks.
According to MSDN[^] I have to activate IAudioClient from an IMMDevice before I finally can call Initialize on the client and start requesting services like ISimpleVolumeControl or IAudioSessionControl by calling GetService. You can see my implementation in the second comment block (that's WASAPI).
However, my implementation is not working. I get an exception saying the reference is not set to an object. That's why I'm using IAudioSessionManager to acquire the controls.

I would be very thankful for any hints to solve this issue ;)
Ah, and before I forget. I'm using the CoreAudio wrappers from Vannatech[^].

Thanks in advance.

So, the code:

Class VolumeManager, a ViewModel will instantiate this.

public sealed class VolumeManager : INotifyPropertyChanged, IDisposable
{
...
    private readonly EventClient _eventClient;
    private readonly IAudioSessionControl _sessionControl;
    private readonly ISimpleAudioVolume _simpleVolume;
...
    public VolumeManager()
    {
        var type = 
            Type.GetTypeFromCLSID( 
                Guid.Parse( ComCLSIDs.MMDeviceEnumeratorCLSID ) );
        IMMDeviceEnumerator deviceEnumerator = 
            (IMMDeviceEnumerator)Activator.CreateInstance( type );

        IMMDevice device;
        Marshal.ThrowExceptionForHR( 
            deviceEnumerator.GetDefaultAudioEndpoint( 
                DataFlow.eRender, 
                ERole.eMultimedia, 
                out device ) );

        // see: http://msdn.microsoft.com/en-us/library/ms886177.aspx
        // CLSCTX_INPROC_SERVER = 0x1
        // CLSCTX_INPROC_HANDLER = 0x2
        // CLSCTX_LOCAL_SERVER = 0x4
        // CLSCTX_REMOTE_SERVER = 0x10
        const uint CLSCTX_ALL = 0x1 | 0x2 | 0x4 | 0x10;

        object obj;
        Marshal.ThrowExceptionForHR( 
            device.Activate( 
                Guid.Parse( ComIIDs.IAudioSessionManagerIID ), 
                CLSCTX_ALL, 
                IntPtr.Zero, 
                out obj ) );
        IAudioSessionManager manager = (IAudioSessionManager)obj;

        // see: http://msdn.microsoft.com/en-        us/library/windows/desktop/dd371455(v=vs.85).aspx

        // Marshal.ThrowExceptionForHR(
        //     device.Activate(
        //         Guid.Parse( ComIIDs.IAudioClientIID ),
        //         CLSCTX_ALL, 
        //         IntPtr.Zero,
        //         out obj ) );
        // IAudioClient client = (IAudioClient)obj;
            
        // int hr = client.Initialize( 
        //     AUDCLNT_SHAREMODE.AUDCLNT_SHAREMODE_SHARED, 
        //     0, 
        //     0,
        //     0,
        //     IntPtr.Zero,
        //     Guid.NewGuid() );
        //
        // says: reference not set to an object ;(
        // Exception ex = Marshal.GetExceptionForHR( hr );

        // client.GetService( 
        //     Guid.Parse( ComIIDs.IAudioSessionControlIID ), out obj );
        // _sessionControl = (IAudioSessionControl)obj;

        // client.GetService( 
        //     Guid.Parse( ComIIDs.ISimpleAudioVolumeIID ), out obj );
        // _simpleVolume = (ISimpleAudioVolume)obj;
            
        Marshal.ThrowExceptionForHR( 
               manager.GetAudioSessionControl( 
                   streamFlags: 0, 
                   sessionControl: out _sessionControl ) );
        Marshal.ThrowExceptionForHR( 
               manager.GetSimpleAudioVolume( 
                   streamFlags: 0, 
                   audioVolume: out _simpleVolume ) );

        // Marshal.ThrowExceptionForHR( 
        //     manager.GetAudioSessionControl( 
        //         Guid.Empty, 
        //         0,
        //         out _sessionControl ) );
        // Marshal.ThrowExceptionForHR( 
        //     manager.GetSimpleAudioVolume( 
        //         Guid.Empty,
        //         0,
        //         out _simpleVolume ) );

        Marshal.ThrowExceptionForHR( 
            Marshal.FinalReleaseComObject( deviceEnumerator ) );
        Marshal.ThrowExceptionForHR( 
            Marshal.FinalReleaseComObject( device ) );
        Marshal.ThrowExceptionForHR( 
            Marshal.FinalReleaseComObject( manager ) );

        _eventClient = new EventClient();
        Marshal.ThrowExceptionForHR( 
            _sessionControl.RegisterAudioSessionNotification( _eventClient ) );

        _eventClient.VolumeChanged += OnVolumeChanged;
    }

...

    // remarks: e.Volume is float [0,1]
    private void OnVolumeChanged( object sender, VolumeEventArgs e )
    {
        IsMuted = e.IsMuted;
        int scalar = Convert.ToInt32( (e.Volume * 100) + 0.5 );
        Volume = scalar;
    }

...
    private int _volume;
    public int Volume
    {
        get
        {
            return _volume;
        }

        set
        {
            if ( _volume == value )
            {
                return;
            }

            int ihr = -1;
            if ( value < 0 )
            {
                ihr = _simpleVolume.SetMasterVolume( 0, Guid.Empty );
            }

            if ( value > 100 )
            {
                ihr = _simpleVolume.SetMasterVolume( 1, Guid.Empty );
            }

            float scalar = Convert.ToSingle( (double)value / 100 );
            int hr = _simpleVolume.SetMasterVolume( scalar, Guid.Empty );

            if ( hr == 0 || ihr == 0)
            {
                _volume = value;
                OnPropertyChanged( "Volume" );
            }
        }
    }

...

    public void Dispose()
    {
        _sessionControl.UnregisterAudioSessionNotification( _eventClient );
        Marshal.FinalReleaseComObject( _simpleVolume );
        Marshal.FinalReleaseComObject( _sessionControl );
    }

...

}

Class EventClient:

internal class EventClient : IAudioSessionEvents
{
    public delegate void VolumeEventHandler( object sender, VolumeEventArgs e );
    public event VolumeEventHandler VolumeChanged;

...

    public int OnSimpleVolumeChanged( float volume, bool isMuted, ref Guid eventContext )
    {
        if ( VolumeChanged != null )
        {
            var args = new VolumeEventArgs( volume, isMuted, eventContext );
            VolumeChanged( this, args );
        }
           
        return 0;
    }