控制音量及平衡

当你做一个多媒体播放器时，难免少不了控制音量的大小和左右声道的播放，下面就介绍一种控制Wave波形输出设备音量的方法，该方法不是设置主音量。先在窗体上放两个TTrackBar，分别命名为TrackBar1，TrackBar2，属性Max都设置为65535，如果觉得刻度太密了，可以把Frequency属性值设置大一些，然后在Uses段加入MMSystem，并在TrackBar1和TrackBar2的OnChange事件都写上下列语句：

procedure TForm1.TrackBar1Change(Sender: Tobject);
var Wave:string;
begin
Wave:='$'+inttohex(TrackBar1.Position,4)+inttohex(TrackBar2.Position,4);
waveoutsetvolume(0,strtoint(Wave));
end;
/////////////////////////////////////////////
WaveOutSetVolume(hwo: Integer; dwVolume: Cardinal);

hwo is MediaPlayer1.DeviceId,

example:                           Right\/ | Left\/
dwVolume for Full L+R = $FFFFFFFF
dwVolume for Full L no R = $0000FFFF
dwVolume for Full R no L = $FFFF0000
dwVolume for no sound = $00000000
/////////////////////////////////////////////////

uses  MMSystem

type
  TVolType = (vtLeft, vtRight);
  TVol = array[vtLeft..vtRight] of word;

procedure TVolForm.GetVolumes(var DevId : word;
                            var VolLeft, VolRight : word);
{volume is returned as a pointer to a DWord with the most
 significant word for the left channel. The channels are
 extracted by treating the DWord as a two element array and
 accessing the two array elements for the Lt and Rt volumes}
var
  Error : integer;
  MsgResponse : word;
  TempVol : TVol;
begin
  Error := AuxGetVolume(DevId, @TempVol);
  if Error <> 0 then begin
    Timer1.Enabled := false;
    MsgResponse := MessageDlg('Error Reading Volume : ' + IntToStr(Error) +
chr(13)
                              + 'DevId : ' + IntToStr(DevId) + chr(13)
                              + chr(13)
                              + 'Set Next Device ?',
                              mtError, [mbYes, mbCancel], 0);
    if MsgResponse = mrYes then {try the next Device Id}
      DevId := DevId + 1
    else begin
      DevId := 0;
      PChangeType := Nil;
    end; {else MsgResponse = mrCancel}
    Exit;
  end; {if Error <> 0}
  VolLeft := TempVol[vtLeft];
  VolRight := TempVol[vtRight];
end;

procedure TVolForm.SetVolumes(DevId : word;
                            var VolLeft, VolRight : word);
{volume is set by passing a DWord value with the most
 significant word set for the left channel, and the least
 significant word set for the right channel. The channels are
 set by treating the DWord as a two element  array and
 setting the two array elements for the Lt and Rt volumes}
var
  Error : integer;
  TempVol : TVol;
begin
  TempVol[vtLeft] := VolLeft;
  TempVol[vtRight] := VolRight;
  Error := AuxSetVolume(DevId, longint(TempVol));
  if Error <> 0 then
    MessageDlg('Error Setting Volume : ' + IntToStr(Error),
               mtError, [mbOK], 0);
end;