Volume.exe: Set volume control levels using Visual Basic

  Form1.frm    - the main form in the project
  Module1.bas  - the module containing the function and type declarations.
  Project1.vbp - the project file
  Project1.vbw - the project workspace file
  Readme.txt   - you are currently reading this file.

• GlobalAlloc - allocates the specified number of bytes from the heap.
• GlobalLock - locks a global memory object and returns a pointer to the first byte of the object's memory block. The memory block associated with a locked memory object cannot be moved or discarded.
• GlobalFree - frees the specified global memory object and invalidates its handle.
• mixerClose - closes the specified mixer device.
• mixerGetControlDetails - retrieves details about a single control associated with an audio line.
• mixerGetDevCaps - queries a specified mixer device to determine its capabilities.
• mixerGetID - retrieves the device identifier for a mixer device associated with a specified device handle.
• mixerGetLineControls - retrieves one or more controls associated with an audio line.
• mixerGetLineInfo - retrieves information about a specific line of a mixer device.
• mixerGetNumDevs - retrieves the number of mixer devices present in the system.
• mixerMessage - sends a custom mixer driver message directly to a mixer driver.
• mixerOpen - opens a specified mixer device and ensures that the device will not be removed until the application closes the handle.
• mixerSetControlDetails - sets properties of a single control associated with an audio line.

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Create the Sample Project

1. Start a new Standard EXE project in Visual Basic. Form1 is created by default.
2. Add two command buttons, two text boxes, and two labels to Form1.
3. Add a Module to the project by completing the following steps:
   1. From the Project menu, click Add module. The Add Module dialog box appears.
   2. From the New tab, choose Module and click OK. A new module is added to your project.
4. Copy the following code to the Code window of Module1:

         Option Explicit
   
         Public Const MMSYSERR_NOERROR = 0
         Public Const MAXPNAMELEN = 32
         Public Const MIXER_LONG_NAME_CHARS = 64
         Public Const MIXER_SHORT_NAME_CHARS = 16
         Public Const MIXER_GETLINEINFOF_COMPONENTTYPE = &H3&
         Public Const MIXER_GETCONTROLDETAILSF_VALUE = &H0&
         Public Const MIXER_GETLINECONTROLSF_ONEBYTYPE = &H2&
         Public Const MIXERLINE_COMPONENTTYPE_DST_FIRST = &H0&
         Public Const MIXERLINE_COMPONENTTYPE_SRC_FIRST = &H1000&
   
         Public Const MIXERLINE_COMPONENTTYPE_DST_SPEAKERS = _
                        (MIXERLINE_COMPONENTTYPE_DST_FIRST + 4)
   
         Public Const MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE = _
                        (MIXERLINE_COMPONENTTYPE_SRC_FIRST + 3)
   
         Public Const MIXERLINE_COMPONENTTYPE_SRC_LINE = _
                        (MIXERLINE_COMPONENTTYPE_SRC_FIRST + 2)
   
         Public Const MIXERCONTROL_CT_CLASS_FADER = &H50000000
         Public Const MIXERCONTROL_CT_UNITS_UNSIGNED = &H30000
   
         Public Const MIXERCONTROL_CONTROLTYPE_FADER = _
                        (MIXERCONTROL_CT_CLASS_FADER Or _
                        MIXERCONTROL_CT_UNITS_UNSIGNED)
   
         Public Const MIXERCONTROL_CONTROLTYPE_VOLUME = _
                        (MIXERCONTROL_CONTROLTYPE_FADER + 1)
   
         Declare Function mixerClose Lib "winmm.dll" _
                        (ByVal hmx As Long) As Long
   
         Declare Function mixerGetControlDetails Lib "winmm.dll" _
                        Alias "mixerGetControlDetailsA" _
                        (ByVal hmxobj As Long, _
                        pmxcd As MIXERCONTROLDETAILS, _
                        ByVal fdwDetails As Long) As Long
   
         Declare Function mixerGetDevCaps Lib "winmm.dll" _
                        Alias "mixerGetDevCapsA" _
                        (ByVal uMxId As Long, _
                        ByVal pmxcaps As MIXERCAPS, _
                        ByVal cbmxcaps As Long) As Long
   
         Declare Function mixerGetID Lib "winmm.dll" _
                        (ByVal hmxobj As Long, _
                        pumxID As Long, _
                        ByVal fdwId As Long) As Long
   
         Declare Function mixerGetLineControls Lib "winmm.dll" _
                        Alias "mixerGetLineControlsA" _
                        (ByVal hmxobj As Long, _
                        pmxlc As MIXERLINECONTROLS, _
                        ByVal fdwControls As Long) As Long
   
         Declare Function mixerGetLineInfo Lib "winmm.dll" _
                        Alias "mixerGetLineInfoA" _
                        (ByVal hmxobj As Long, _
                        pmxl As MIXERLINE, _
                        ByVal fdwInfo As Long) As Long
   
         Declare Function mixerGetNumDevs Lib "winmm.dll" () As Long
   
         Declare Function mixerMessage Lib "winmm.dll" _
                        (ByVal hmx As Long, _
                        ByVal uMsg As Long, _
                        ByVal dwParam1 As Long, _
                        ByVal dwParam2 As Long) As Long
   
         Declare Function mixerOpen Lib "winmm.dll" _
                        (phmx As Long, _
                        ByVal uMxId As Long, _
                        ByVal dwCallback As Long, _
                        ByVal dwInstance As Long, _
                        ByVal fdwOpen As Long) As Long
   
         Declare Function mixerSetControlDetails Lib "winmm.dll" _
                        (ByVal hmxobj As Long, _
                        pmxcd As MIXERCONTROLDETAILS, _
                        ByVal fdwDetails As Long) As Long
   
         Declare Sub CopyStructFromPtr Lib "kernel32" _
                        Alias "RtlMoveMemory" _
                        (struct As Any, _
                        ByVal ptr As Long, _
                        ByVal cb As Long)
   
         Declare Sub CopyPtrFromStruct Lib "kernel32" _
                        Alias "RtlMoveMemory" _
                        (ByVal ptr As Long, _
                        struct As Any, _
                        ByVal cb As Long)
   
         Declare Function GlobalAlloc Lib "kernel32" _
                        (ByVal wFlags As Long, _
                        ByVal dwBytes As Long) As Long
   
         Declare Function GlobalLock Lib "kernel32" _
                        (ByVal hmem As Long) As Long
   
         Declare Function GlobalFree Lib "kernel32" _
                        (ByVal hmem As Long) As Long
   
         Type MIXERCAPS
            wMid As Integer                   '  manufacturer id
            wPid As Integer                   '  product id
            vDriverVersion As Long            '  version of the driver
            szPname As String * MAXPNAMELEN   '  product name
            fdwSupport As Long                '  misc. support bits
            cDestinations As Long             '  count of destinations
         End Type
   
         Type MIXERCONTROL
            cbStruct As Long           '  size in Byte of MIXERCONTROL
            dwControlID As Long        '  unique control id for mixer device
            dwControlType As Long      '  MIXERCONTROL_CONTROLTYPE_xxx
            fdwControl As Long         '  MIXERCONTROL_CONTROLF_xxx
            cMultipleItems As Long     '  if MIXERCONTROL_CONTROLF_MULTIPLE
                                       '  set
            szShortName As String * MIXER_SHORT_NAME_CHARS  ' short name of
                                                            ' control
            szName As String * MIXER_LONG_NAME_CHARS        ' long name of
                                                            ' control
            lMinimum As Long           '  Minimum value
            lMaximum As Long           '  Maximum value
            reserved(10) As Long       '  reserved structure space
            End Type
   
         Type MIXERCONTROLDETAILS
            cbStruct As Long       '  size in Byte of MIXERCONTROLDETAILS
            dwControlID As Long    '  control id to get/set details on
            cChannels As Long      '  number of channels in paDetails array
            item As Long           '  hwndOwner or cMultipleItems
            cbDetails As Long      '  size of _one_ details_XX struct
            paDetails As Long      '  pointer to array of details_XX structs
         End Type
   
         Type MIXERCONTROLDETAILS_UNSIGNED
            dwValue As Long        '  value of the control
         End Type
   
         Type MIXERLINE
            cbStruct As Long               '  size of MIXERLINE structure
            dwDestination As Long          '  zero based destination index
            dwSource As Long               '  zero based source index (if
                                           '  source)
            dwLineID As Long               '  unique line id for mixer device
            fdwLine As Long                '  state/information about line
            dwUser As Long                 '  driver specific information
            dwComponentType As Long        '  component type line connects to
            cChannels As Long              '  number of channels line supports
            cConnections As Long           '  number of connections (possible)
            cControls As Long              '  number of controls at this line
            szShortName As String * MIXER_SHORT_NAME_CHARS
            szName As String * MIXER_LONG_NAME_CHARS
            dwType As Long
            dwDeviceID As Long
            wMid  As Integer
            wPid As Integer
            vDriverVersion As Long
            szPname As String * MAXPNAMELEN
         End Type
   
         Type MIXERLINECONTROLS
            cbStruct As Long       '  size in Byte of MIXERLINECONTROLS
            dwLineID As Long       '  line id (from MIXERLINE.dwLineID)
                                   '  MIXER_GETLINECONTROLSF_ONEBYID or
            dwControl As Long      '  MIXER_GETLINECONTROLSF_ONEBYTYPE
            cControls As Long      '  count of controls pmxctrl points to
            cbmxctrl As Long       '  size in Byte of _one_ MIXERCONTROL
            pamxctrl As Long       '  pointer to first MIXERCONTROL array
         End Type
   
         Function GetVolumeControl(ByVal hmixer As Long, _
                                 ByVal componentType As Long, _
                                 ByVal ctrlType As Long, _
                                 ByRef mxc As MIXERCONTROL) As Boolean
   
         ' This function attempts to obtain a mixer control.
         ' Returns True if successful.
            Dim mxlc As MIXERLINECONTROLS
            Dim mxl As MIXERLINE
            Dim hmem As Long
            Dim rc As Long
   
            mxl.cbStruct = Len(mxl)
            mxl.dwComponentType = componentType
   
            ' Obtain a line corresponding to the component type
            rc = mixerGetLineInfo(hmixer, _
                                  mxl, _
                                  MIXER_GETLINEINFOF_COMPONENTTYPE)
   
            If (MMSYSERR_NOERROR = rc) Then
                mxlc.cbStruct = Len(mxlc)
                mxlc.dwLineID = mxl.dwLineID
                mxlc.dwControl = ctrlType
                mxlc.cControls = 1
                mxlc.cbmxctrl = Len(mxc)
   
                ' Allocate a buffer for the control
                hmem = GlobalAlloc(&H40, Len(mxc))
                mxlc.pamxctrl = GlobalLock(hmem)
                mxc.cbStruct = Len(mxc)
   
                ' Get the control
                rc = mixerGetLineControls(hmixer, _
                                          mxlc, _
                                          MIXER_GETLINECONTROLSF_ONEBYTYPE)
   
                If (MMSYSERR_NOERROR = rc) Then
                    GetVolumeControl = True
   
                    ' Copy the control into the destination structure
                    CopyStructFromPtr mxc, mxlc.pamxctrl, Len(mxc)
                Else
                    GetVolumeControl = False
                End If
                GlobalFree (hmem)
                Exit Function
            End If
   
            GetVolumeControl = False
         End Function
   
         Function SetVolumeControl(ByVal hmixer As Long, _
                                 mxc As MIXERCONTROL, _
                                 ByVal volume As Long) As Boolean
         ' This function sets the value for a volume control.
         ' Returns True if successful
   
            Dim mxcd As MIXERCONTROLDETAILS
            Dim vol As MIXERCONTROLDETAILS_UNSIGNED
   
            mxcd.item = 0
            mxcd.dwControlID = mxc.dwControlID
            mxcd.cbStruct = Len(mxcd)
            mxcd.cbDetails = Len(vol)
   
            ' Allocate a buffer for the control value buffer
            hmem = GlobalAlloc(&H40, Len(vol))
            mxcd.paDetails = GlobalLock(hmem)
            mxcd.cChannels = 1
            vol.dwValue = volume
   
            ' Copy the data into the control value buffer
            CopyPtrFromStruct mxcd.paDetails, vol, Len(vol)
   
            ' Set the control value
            rc = mixerSetControlDetails(hmixer, _
                                       mxcd, _
                                       MIXER_SETCONTROLDETAILSF_VALUE)
   
            GlobalFree (hmem)
            If (MMSYSERR_NOERROR = rc) Then
                SetVolumeControl = True
            Else
                SetVolumeControl = False
            End If
         End Function
   

5. Copy the following code to the Code window of Form1:

         Option Explicit
   
         Dim hmixer As Long          ' mixer handle
         Dim volCtrl As MIXERCONTROL ' waveout volume control
         Dim micCtrl As MIXERCONTROL ' microphone volume control
         Dim rc As Long              ' return code
         Dim ok As Boolean           ' boolean return code
         Dim vol As Long             ' volume  
   
         Private Sub Form_Load()
         ' Open the mixer with deviceID 0.
            rc = mixerOpen(hmixer, 0, 0, 0, 0)
            If ((MMSYSERR_NOERROR <> rc)) Then
                MsgBox "Couldn't open the mixer."
                Exit Sub
                End If
   
            ' Get the waveout volume control
            ok = GetVolumeControl(hmixer, _
                                 MIXERLINE_COMPONENTTYPE_DST_SPEAKERS, _
                                 MIXERCONTROL_CONTROLTYPE_VOLUME, _
                                 volCtrl)
            If (ok = True) Then
                ' If the function successfully gets the volume control,
                ' the maximum and minimum values are specified by
                ' lMaximum and lMinimum
                Label1.Caption = volCtrl.lMinimum _
                                 & " to " _
                                 & volCtrl.lMaximum
                End If
   
            ' Get the microphone volume control
            ok = GetVolumeControl(hmixer, _
                                 MIXERLINE_COMPONENTTYPE_SRC_MICROPHONE, _
                                 MIXERCONTROL_CONTROLTYPE_VOLUME, _
                                 micCtrl)
            If (ok = True) Then
                Label2.Caption = micCtrl.lMinimum _
                                 & " to " _
                                 & micCtrl.lMaximum
                End If
         End Sub
   
         Private Sub Command1_Click()
            vol = CLng(Text1.Text)
            SetVolumeControl hmixer, volCtrl, vol
         End Sub
   
         Private Sub Command2_Click()
            vol = CLng(Text2.Text)
            SetVolumeControl hmixer, micCtrl, vol
         End Sub

6. On the Run menu, click Start or press the F5 key to start the program. Minimize the Visual Basic IDE so all that appears on your display is Form1. Maximize the Volume Level program in the Task bar. Arrange Form1 and the Volume Level program so both programs are visible.
7. Enter a value between the minimum and maximum values shown in one or both text boxes and click one of the command buttons in Form1. Note that the corresponding slider in the Volume Level program is adjusted to your specified level.

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