Volume Mute and SendMessage() Fun

As the owner of the @wincmdfu twitter account, I try and find alternate ways of doing stuff in Windows. I normally have a bunch of batch files, VB script files and powershell cmdlets in a custom folder in %PATH% that I call when required. While listening to some music the other day, I realized there is no shortcut that I know (or have discovered yet) that allows me to mute the Audio on my system. I have a hardware key on the keyboard that mutes the volume, but no command to do this (remotely for example – which is cooler).

Enter the Windows SendMessage API. This is a fantastic API that Windows uses to send messages to windows given the handle of the target window. This window could be in a different process as well. The SendMessage function calls the window procedure for the specified window and does not return until the window procedure has processed the message.

I will be writing about additional fun stuff you can do with the SendMessage API, but for now coming back to my problem statement. SendMessage can be used to send the WM_APPCOMMAND with the APPCOMMAND_VOLUME_MUTE parameter to the current window handle to toggle mute. This can programmatically be put into a Form/console application and run from command line. Here’s my VB.NET code:

[code language=”vb” gutter=”false”]
Public Class Form1

<Runtime.InteropServices.DllImport("user32.dll")> _
Public Shared Function SendMessageW(ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As IntPtr
End Function

Private Const APPCOMMAND_VOLUME_MUTE As Integer = &H80000
Private Const WM_APPCOMMAND As Integer = &H319

Private Sub Main_Load(sender As Object, e As EventArgs) Handles MyBase.Load
SendMessageW(Me.Handle, WM_APPCOMMAND, Me.Handle, APPCOMMAND_VOLUME_MUTE)
End
End Sub
End Class
[/code]

Compile this into an executable called mute.exe, store it in %PATH% and you are done!
Happy Hacking!

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