Title: How to program a peak level meter
uses
MMSystem;
procedure TForm1.Button1Click(Sender: TObject);
var
MixerControl: TMixerControl;
MixerControlDetails: TMixerControlDetails;
MixerControlDetailsSigned: TMixerControlDetailsSigned;
Mixer: THandle;
MixerLine: TMixerLine;
MixerLineControls: TMixerLineControls;
PeakMeter: DWORD;
Rslt: DWORD;
SourceCount: Cardinal;
WaveOut: DWORD;
I: Integer;
X: Integer;
Y: Integer;
begin
Rslt := mixerOpen(@Mixer, 0, 0, 0, 0);
if Rslt 0 then
raise Exception.CreateFmt('Can''t open mixer (%d)', [Rslt]);
FillChar(MixerLine, SizeOf(MixerLine), 0);
MixerLine.cbStruct := SizeOf(MixerLine);
MixerLine.dwComponentType := MIXERLINE_COMPONENTTYPE_DST_SPEAKERS;
Rslt := mixerGetLineInfo(Mixer, @MixerLine,
MIXER_GETLINEINFOF_COMPONENTTYPE);
if Rslt 0 then
raise Exception.CreateFmt('Can''t find speaker line (%d)', [Rslt]);
SourceCount := MixerLine.cConnections;
WaveOut := $FFFFFFFF;
for I := 0 to SourceCount - 1 do
begin
MixerLine.dwSource := I;
Rslt := mixerGetLineInfo(Mixer, @MixerLine,
MIXER_GETLINEINFOF_SOURCE);
if Rslt 0 then
raise Exception.CreateFmt('Can''t get source line (%d)', [Rslt]);
if MixerLine.dwComponentType = MIXERLINE_COMPONENTTYPE_SRC_WAVEOUT then
begin
WaveOut := MixerLine.dwLineId;
Break;
end;
end;
if WaveOut = $FFFFFFFF then
raise Exception.Create('Can''t find wave out device');
FillChar(MixerLineControls, SizeOf(MixerLineControls), 0);
with MixerLineControls do
begin
cbStruct := SizeOf(MixerLineControls);
dwLineId := WaveOut;
dwControlType := MIXERCONTROL_CONTROLTYPE_PEAKMETER;
cControls := 1;
cbmxctrl := SizeOf(TMixerControl);
pamxctrl := @MixerControl;
end;
Rslt := mixerGetLineControls(Mixer, @MixerLineControls,
MIXER_GETLINECONTROLSF_ONEBYTYPE);
if Rslt 0 then
raise Exception.CreateFmt('Can''t find peak meter control (%d)',
[Rslt]);
PeakMeter := MixerControl.dwControlID;
// at this point, I have the meter control ID, so I can
// repeatedly query its value and plot the resulting data
// on a canvas
X := 0;
FillChar(MixerControlDetails, SizeOf(MixerControlDetails), 0);
with MixerControlDetails do
begin
cbStruct := SizeOf(MixerControlDetails);
dwControlId := PeakMeter;
cChannels := 1;
cbDetails := SizeOf(MixerControlDetailsSigned);
paDetails := @MixerControlDetailsSigned;
end;
repeat
Sleep(10);
Rslt := mixerGetControlDetails(Mixer, @MixerControlDetails,
MIXER_GETCONTROLDETAILSF_VALUE);
if Rslt 0 then
raise Exception.CreateFmt('Can''t get control details (%d)',
[Rslt]);
Application.ProcessMessages;
Inc(X);
Y := 300 - Round(300 * Abs(MixerControlDetailsSigned.lValue) / 32768);
with Canvas do
begin
MoveTo(X, 0);
Pen.Color := clBtnFace;
LineTo(X, 300);
Pen.Color := clWindowText;
LineTo(X, Y);
end;
until X 500;
// don't forget to close the mixer handle when you're done
Rslt := mixerClose(Mixer);
if Rslt 0 then
raise Exception.CreateFmt('Can''t close mixer (%d)', [Rslt]);
end;