'按钮一是音量增加,按钮二是音量减少,按钮三是静音切换.
Option Explicit

Private Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" ( _
ByVal hwnd As Long, _
ByVal wMsg As Long, _
ByVal wParam As Long, _
ByVal lParam As Long) As Long

Private Const WM_APPCOMMAND As Long = &H319
Private Const APPCOMMAND_VOLUME_UP As Long = 10
Private Const APPCOMMAND_VOLUME_DOWN As Long = 9
Private Const APPCOMMAND_VOLUME_MUTE As Long = 8

Private Sub Command1_Click()
'音量增加
SendMessage Me.hwnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_UP * &H10000
End Sub

Private Sub Command2_Click()
'音量减少
SendMessage Me.hwnd, WM_APPCOMMAND, &H30292, APPCOMMAND_VOLUME_DOWN * &H10000
End Sub

Private Sub Command3_Click()
'静音
SendMessage Me.hwnd, WM_APPCOMMAND, &H200EB0, APPCOMMAND_VOLUME_MUTE * &H10000
End Sub