Author: Tomas Rutkauskas

How can I set the master volume? I don't want to use an external file like a DLL.

Answer:

Solve 1:

The "Mixer" parameter of SetMasterVolume has to be either a mixer device ID in the 
range 0..mixerGetNumDevs-1 or a mixer handle returned by a call to mixerOpen().


1   interface
2   
3   uses
4     SysUtils, Windows, MMSystem;
5   
6   procedure SetMasterVolume(Mixer: hMixerObj; Value: Word);
7   
8   implementation
9   
10  function GetMasterVolumeControl(Mixer: hMixerObj; var Control: TMixerControl): 
11  MMResult;
12  {Returns True on success}
13  var
14    Line: TMixerLine;
15    Controls: TMixerLineControls;
16  begin
17    ZeroMemory(@Line, SizeOf(Line));
18    Line.cbStruct := SizeOf(Line);
19    Line.dwComponentType := MIXERLINE_COMPONENTTYPE_DST_SPEAKERS;
20    Result := mixerGetLineInfo(Mixer, @Line, MIXER_GETLINEINFOF_COMPONENTTYPE);
21    if Result = MMSYSERR_NOERROR then
22    begin
23      ZeroMemory(@Controls, SizeOf(Controls));
24      Controls.cbStruct := SizeOf(Controls);
25      Controls.dwLineID := Line.dwLineID;
26      Controls.cControls := 1;
27      Controls.dwControlType := MIXERCONTROL_CONTROLTYPE_VOLUME;
28      Controls.cbmxctrl := SizeOf(Control);
29      Controls.pamxctrl := @Control;
30      Result := mixerGetLineControls(Mixer, @Controls, 
31  MIXER_GETLINECONTROLSF_ONEBYTYPE);
32    end;
33  end;
34  
35  procedure SetMasterVolume(Mixer: hMixerObj; Value: Word);
36  var
37    MasterVolume: TMixerControl;
38    Details: TMixerControlDetails;
39    UnsignedDetails: TMixerControlDetailsUnsigned;
40    Code: MMResult;
41  begin
42    Code := GetMasterVolumeControl(Mixer, MasterVolume);
43    if Code = MMSYSERR_NOERROR then
44    begin
45      with Details do
46      begin
47        cbStruct := SizeOf(Details);
48        dwControlID := MasterVolume.dwControlID;
49        cChannels := 1; {set all channels}
50        cMultipleItems := 0;
51        cbDetails := SizeOf(UnsignedDetails);
52        paDetails := @UnsignedDetails;
53      end;
54      UnsignedDetails.dwValue := Value;
55      Code := mixerSetControlDetails(Mixer, @Details, MIXER_SETCONTROLDETAILSF_VALUE);
56    end;
57    if Code <> MMSYSERR_NOERROR then
58      raise Exception.CreateFmt('SetMasterVolume failure, ' + 'multimedia system 
59  error #%d'
60  end;



Solve 2:

61  uses
62    MMSystem;
63  
64  function GetVolumeControl(aMixer: HMixer; componentType, ctrlType: Longint;
65    var mxc: TMixerControl): Boolean;
66  var
67    mxl: TMixerLine;
68    mxlc: TMixerLineControls;
69    rc: Longint;
70  begin
71    Result := FALSE;
72    FillChar(mxl, SizeOf(TMixerLine), 0);
73    mxl.cbStruct := SizeOf(TMixerLine);
74    mxl.dwComponentType := componentType;
75    {Obtain a line corresponding to the component type}
76    rc := mixerGetLineInfo(aMixer, @mxl, MIXER_GETLINEINFOF_COMPONENTTYPE);
77    if rc = MMSYSERR_NOERROR then
78    begin
79      mxlc.cbStruct := SizeOf(TMixerLineControls);
80      mxlc.dwLineID := mxl.dwLineID;
81      mxlc.dwControlType := ctrlType;
82      mxlc.cControls := 1;
83      mxlc.cbmxctrl := SizeOf(TMixerLine);
84      mxlc.pamxctrl := @mxc;
85      mxlc.pamxctrl^.cbStruct := SizeOf(TMixerControl);
86      mixerGetLineControls(aMixer, @mxlc, MIXER_GETLINECONTROLSF_ONEBYTYPE);
87      rc := mixerGetLineControls(aMixer, @mxlc, MIXER_GETLINECONTROLSF_ONEBYTYPE);
88      Result := rc = MMSYSERR_NOERROR;
89    end;
90  end;
91  
92  function SetVolumeControl(aMixer: HMixer; mxc: TMixerControl; volume:
93    LongInt): Boolean;
94  var
95    mxcd: TMixerControlDetails;
96    vol: TMixerControlDetails_Unsigned;
97    rc: MMRESULT;
98  begin
99    FillChar(mxcd, SizeOf(mxcd), 0);
100   mxcd.dwControlID := mxc.dwControlID;
101   mxcd.cbStruct := SizeOf(TMixerControlDetails);
102   mxcd.cbDetails := SizeOf(TMixerControlDetails_Unsigned);
103   mxcd.paDetails := @vol;
104   mxcd.cChannels := 1;
105   vol.dwValue := volume;
106   rc := mixerSetControlDetails(aMixer, @mxcd, MIXER_SETCONTROLDETAILSF_VALUE);
107   Result := rc = MMSYSERR_NOERROR;
108 end;
109 
110 function InitMixer: HMixer;
111 var
112   Err: MMRESULT;
113 begin
114   Err := mixerOpen(@Result, 0, 0, 0, 0);
115   if Err <> MMSYSERR_NOERROR then
116     Result := 0;
117 end;
118 
119 
120 //Usage example:
121 
122 
123 procedure SetMasterVolumeToZero;
124 var
125   MyMixerHandle: HMixer;
126   MyVolCtrl: TMixerControl;
127 begin
128   MyMixerHandle := InitMixer;
129   if MyMixerHandle <> 0 then
130   try
131     FillChar(MyVolCtrl, SizeOf(MyVolCtrl), 0);
132     if GetVolumeControl(MyMixerHandle, MIXERLINE_COMPONENTTYPE_DST_SPEAKERS,
133       MIXERCONTROL_CONTROLTYPE_VOLUME, MyVolCtrl) then
134     begin
135       {The last parameter (0) here is the volume level}
136       if SetVolumeControl(MyMixer, MyVolCtrl, 0) then
137         ShowMessage('Volume should now be set to zero');
138     end;
139   finally
140     mixerClose(MyMixer);
141   end;
142 end;