Example1

unit Unit33;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, MMDevApi, ActiveX, StdCtrls;

type
  TForm33 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form33: TForm33;
  endpointVolume: IAudioEndpointVolume = nil;

implementation

{$R *.dfm}


procedure TForm33.Button1Click(Sender: TObject);
var
  VolumeLevel: Single;
begin
  if endpointVolume = nil then Exit;
  VolumeLevel := 0.50;
  endpointVolume.SetMasterVolumeLevelScalar(VolumeLevel, nil);
  Caption := Format('%1.8f', [VolumeLevel])
end;

procedure TForm33.FormCreate(Sender: TObject);
var
  deviceEnumerator: IMMDeviceEnumerator;
  defaultDevice: IMMDevice;
begin
  CoCreateInstance(CLASS_IMMDeviceEnumerator, nil, CLSCTX_INPROC_SERVER, IID_IMMDeviceEnumerator, deviceEnumerator);
  deviceEnumerator.GetDefaultAudioEndpoint(eRender, eConsole, defaultDevice);
  defaultDevice.Activate(IID_IAudioEndpointVolume, CLSCTX_INPROC_SERVER, nil, endpointVolume);
end;

end.