Control the system volume from UWP, using the IAudioEndpointVolume interface

VolumeControl.cs

s/---
// Control the system volume from UWP, using the IAudioEndpointVolume interface
//
// Wim Bokkers
//
// Credits:
// * Reddit user sunius (https://www.reddit.com/user/sunius)
//    See this thread: https://www.reddit.com/r/WPDev/comments/4kqzkb/launch_exe_with_parameter_in_uwp/d3jepi7/
//    And this code: https://pastebin.com/cPhVCyWj
//
// The code provided by sunius has two major drawbacks:
//   - It uses unsafe code
//   - It does not work in Release mode (the app crashes)
//
// Marshalling the Guid pointers as out parameters will fix this.
//
// This code is also available from: https://gist.github.com/wbokkers/74e05ccc1ee2371ec55c4a7daf551a26
//---

using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Threading;
using Windows.Media.Devices;

namespace AudioUtils
{
    internal enum HResult : uint
    {
        S_OK = 0
    }

    public static class VolumeControl
    {
        public static void ChangeVolumeToMinLevel(double level)
        {
            if (level > 1)
                level = 1;
            else if (level < 0)
                level = 0;

            try
            {
                var masterVol = GetAudioEndpointVolumeInterface();
                if (masterVol == null)
                    return;

                // Make sure that the audio is not muted
                masterVol.SetMute(false, Guid.Empty);

                // Only adapt volume if the current level is below the specified minimum level
                var currentAudioValue = masterVol.GetMasterVolumeLevelScalar();
                float newAudioValue = Convert.ToSingle(level);
                if (currentAudioValue > newAudioValue)
                    return;

                masterVol.SetMasterVolumeLevelScalar(newAudioValue, Guid.Empty);
            }
            catch { }
        }

        private static IAudioEndpointVolume GetAudioEndpointVolumeInterface()
        {
            var speakerId = MediaDevice.GetDefaultAudioRenderId(AudioDeviceRole.Default);
            var completionHandler = new ActivateAudioInterfaceCompletionHandler<IAudioEndpointVolume>();

            var hr = ActivateAudioInterfaceAsync(
                speakerId,
                typeof(IAudioEndpointVolume).GetTypeInfo().GUID,
                IntPtr.Zero,
                completionHandler,
                out var activateOperation);

            Debug.Assert(hr == (uint)HResult.S_OK);

            return completionHandler.WaitForCompletion();
        }

        [DllImport("Mmdevapi.dll", ExactSpelling = true, PreserveSig = false)]
        [return: MarshalAs(UnmanagedType.Error)]
        private static extern uint ActivateAudioInterfaceAsync(
                [In, MarshalAs(UnmanagedType.LPWStr)]string deviceInterfacePath,
                [In, MarshalAs(UnmanagedType.LPStruct)]Guid riid,
                [In] IntPtr activationParams,
                [In] IActivateAudioInterfaceCompletionHandler completionHandler,
                out IActivateAudioInterfaceAsyncOperation activationOperation);

        internal class ActivateAudioInterfaceCompletionHandler<T> : IActivateAudioInterfaceCompletionHandler
        {
            private AutoResetEvent _completionEvent;
            private T _result;

            public ActivateAudioInterfaceCompletionHandler()
            {
                _completionEvent = new AutoResetEvent(false);
            }

            public void ActivateCompleted(IActivateAudioInterfaceAsyncOperation operation)
            {
                operation.GetActivateResult(out var hr, out var activatedInterface);

                Debug.Assert(hr == (uint)HResult.S_OK);

                _result = (T)activatedInterface;

                var setResult = _completionEvent.Set();
                Debug.Assert(setResult != false);
            }

            public T WaitForCompletion()
            {
                var waitResult = _completionEvent.WaitOne();
                Debug.Assert(waitResult != false);

                return _result;
            }
        }
    }

    [ComImport]
    [Guid("5CDF2C82-841E-4546-9722-0CF74078229A"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    internal interface IAudioEndpointVolume
    {
        void NotImpl1();

        void NotImpl2();

        [return: MarshalAs(UnmanagedType.U4)]
        uint GetChannelCount();

        void SetMasterVolumeLevel(
            [In] [MarshalAs(UnmanagedType.R4)] float level,
            [In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);

        void SetMasterVolumeLevelScalar(
            [In] [MarshalAs(UnmanagedType.R4)] float level,
            [In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);

        [return: MarshalAs(UnmanagedType.R4)]
        float GetMasterVolumeLevel();

        [return: MarshalAs(UnmanagedType.R4)]
        float GetMasterVolumeLevelScalar();

        void SetChannelVolumeLevel(
            [In] [MarshalAs(UnmanagedType.U4)] uint channelNumber,
            [In] [MarshalAs(UnmanagedType.R4)] float level,
            [In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);

        void SetChannelVolumeLevelScalar(
            [In] [MarshalAs(UnmanagedType.U4)] uint channelNumber,
            [In] [MarshalAs(UnmanagedType.R4)] float level,
            [In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);

        void GetChannelVolumeLevel(
            [In] [MarshalAs(UnmanagedType.U4)] uint channelNumber,
            [Out] [MarshalAs(UnmanagedType.R4)] out float level);

        [return: MarshalAs(UnmanagedType.R4)]
        float GetChannelVolumeLevelScalar([In] [MarshalAs(UnmanagedType.U4)] uint channelNumber);

        void SetMute(
            [In] [MarshalAs(UnmanagedType.Bool)] bool isMuted,
            [In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);

        [return: MarshalAs(UnmanagedType.Bool)]
        bool GetMute();

        void GetVolumeStepInfo(
            [Out] [MarshalAs(UnmanagedType.U4)] out uint step,
            [Out] [MarshalAs(UnmanagedType.U4)] out uint stepCount);

        void VolumeStepUp([In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);

        void VolumeStepDown([In] [MarshalAs(UnmanagedType.LPStruct)] Guid eventContext);

        [return: MarshalAs(UnmanagedType.U4)] // bit mask
        uint QueryHardwareSupport();

        void GetVolumeRange(
            [Out] [MarshalAs(UnmanagedType.R4)] out float volumeMin,
            [Out] [MarshalAs(UnmanagedType.R4)] out float volumeMax,
            [Out] [MarshalAs(UnmanagedType.R4)] out float volumeStep);
    }

    [ComImport]
    [Guid("72A22D78-CDE4-431D-B8CC-843A71199B6D")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    internal interface IActivateAudioInterfaceAsyncOperation
    {
        void GetActivateResult(
            [MarshalAs(UnmanagedType.Error)]out uint activateResult,
            [MarshalAs(UnmanagedType.IUnknown)]out object activatedInterface);
    }

    [ComImport]
    [Guid("41D949AB-9862-444A-80F6-C261334DA5EB")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    internal interface IActivateAudioInterfaceCompletionHandler
    {
        void ActivateCompleted(IActivateAudioInterfaceAsyncOperation activateOperation);
    }
}

Please do not just copy+paste this code. It needs better error handling (and not swallowing all exceptions).

Hi,
I used your code VolumeControl to adjust the master volume level from my UWP app and it works very well. I would though like to set the volume for my app separately without changing the master volume.
I tried to set volume using SetChannelVolumeLevelScalar without success. ChannelCount shows 2 channels found. I tried both channel 0 and 1 with the following code.
` Public Sub SetChannelVolume(ByVal Channel As Integer, ByVal Level As Double)
If Level > 1 Then
Level = 1
ElseIf Level < 0 Then
Level = 0
End If

    Try
        Dim channelVol = GetAudioEndpointVolumeInterface()
        If channelVol Is Nothing Then
            Return
        End If

        ' Make sure that the audio is not muted
        channelVol.SetMute(False, Guid.Empty)

        Dim newAudioValue As Single = Convert.ToSingle(Level)

        channelVol.SetChannelVolumeLevelScalar(Channel, newAudioValue, Guid.Empty)
    Catch
    End Try
End Sub

`
Would you be so kind to point me in the right direction.
Thank you in advance,
Henrik

Thanks for your help, your work helps a lot in my UWP apps developing when I am a loss to deal with it with a deadline.