How to programmatically set the system volume?

How can I change the Windows System Sound Volume using a C# Application?

I'm a bit late to the party but if you are looking now there's a nuget package available (AudioSwitcher.AudioApi.CoreAudio) that simplifies audio interactions. Install it then it’s as simple as:

CoreAudioDevice defaultPlaybackDevice = new CoreAudioController().DefaultPlaybackDevice;
Debug.WriteLine("Current Volume:" + defaultPlaybackDevice.Volume);
defaultPlaybackDevice.Volume = 80;

Here is the code:

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
 
namespace Test
{
    public class Test
    {
        private const int APPCOMMAND_VOLUME_MUTE = 0x80000;
        private const int APPCOMMAND_VOLUME_UP = 0xA0000;
        private const int APPCOMMAND_VOLUME_DOWN = 0x90000;
        private const int WM_APPCOMMAND = 0x319;
 
        [DllImport("user32.dll")]
        public static extern IntPtr SendMessageW(IntPtr hWnd, int Msg,
            IntPtr wParam, IntPtr lParam);
 
        private void Mute()
        {
            SendMessageW(this.Handle, WM_APPCOMMAND, this.Handle,
                (IntPtr)APPCOMMAND_VOLUME_MUTE);
        }
 
        private void VolDown()
        {
            SendMessageW(this.Handle, WM_APPCOMMAND, this.Handle,
                (IntPtr)APPCOMMAND_VOLUME_DOWN);
        }
 
        private void VolUp()
        {
            SendMessageW(this.Handle, WM_APPCOMMAND, this.Handle,
                (IntPtr)APPCOMMAND_VOLUME_UP);
        }
    }
}

Found on dotnetcurry

When using WPF you need to use new WindowInteropHelper(this).Handle instead of this.Handle (thanks Alex Beals)

If the tutorials provided in the other answers are too involved you could try an implementation like this using the keybd_event function

[DllImport("user32.dll")]
static extern void keybd_event(byte bVk, byte bScan, uint dwFlags, int dwExtraInfo);

Usage:

keybd_event((byte)Keys.VolumeUp, 0, 0, 0); // increase volume
keybd_event((byte)Keys.VolumeDown, 0, 0, 0); // decrease volume

In case you wish to set it to an exact value using the Core Audio APIs:

using CoreAudioApi;

public class SystemVolumeConfigurator
{
        private readonly MMDeviceEnumerator _deviceEnumerator = new MMDeviceEnumerator();
        private readonly MMDevice _playbackDevice;

        public SystemVolumeConfigurator()
        {
            _playbackDevice = _deviceEnumerator.GetDefaultAudioEndpoint(EDataFlow.eRender, ERole.eMultimedia);
        }

        public int GetVolume()
        {
            return (int)(_playbackDevice.AudioEndpointVolume.MasterVolumeLevelScalar * 100);
        }

        public void SetVolume(int volumeLevel)
        {
            if (volumeLevel < 0 || volumeLevel > 100)
                throw new ArgumentException("Volume must be between 0 and 100!");

            _playbackDevice.AudioEndpointVolume.MasterVolumeLevelScalar = volumeLevel / 100.0f;
        }
}

You can add this library https://gist.github.com/sverrirs/d099b34b7f72bb4fb386 to your project and change the volume like this;

VideoPlayerController.AudioManager.SetMasterVolume(100);

The library also includes options for changing application volume, mute, getting current volume level etc. The namespace is called "Video Player Controller" but I used it in a Windows Forms App to change the system volume and it worked fine, so the "video" part is arbitrary.

My code is a bit different but still using CoreAudio

downloaded the pkg : nuget install AudioSwitcher.AudioApi.CoreAudio -Version 3.0.0.1

using AudioSwitcher.AudioApi.CoreAudio;
public partial class MainWindow : Window
{
public MainWindow()
{

InitializeComponent();

CoreAudioDevice defaultPlaybackDevice = new CoreAudioController().DefaultPlaybackDevice;

double vol = defaultPlaybackDevice.Volume;

defaultPlaybackDevice.Volume = defaultPlaybackDevice.Volume - 5.0;

defaultPlaybackDevice.Volume = defaultPlaybackDevice.Volume + 5.0;
}
}