volume control using Delphi

it's work in Delphi 7
//////////////////////////

unit MMDevApi;
interface
uses
  Windows, ActiveX, ComObj;
const
  CLASS_IMMDeviceEnumerator             : TGUID = '{BCDE0395-E52F-467C-8E3D-C4579291692E}';
  IID_IMMDeviceEnumerator               : TGUID = '{A95664D2-9614-4F35-A746-DE8DB63617E6}';
  IID_IMMDevice                         : TGUID = '{D666063F-1587-4E43-81F1-B948E807363F}';
  IID_IMMDeviceCollection               : TGUID = '{0BD7A1BE-7A1A-44DB-8397-CC5392387B5E}';
  IID_IAudioEndpointVolume              : TGUID = '{5CDF2C82-841E-4546-9722-0CF74078229A}';
  IID_IAudioMeterInformation            : TGUID = '{C02216F6-8C67-4B5B-9D00-D008E73E0064}';
  IID_IAudioEndpointVolumeCallback      : TGUID = '{657804FA-D6AD-4496-8A60-352752AF4F89}';
  DEVICE_STATE_ACTIVE                   = $00000001;
  DEVICE_STATE_UNPLUGGED                = $00000002;
  DEVICE_STATE_NOTPRESENT               = $00000004;
  DEVICE_STATEMASK_ALL                  = $00000007;
type
  EDataFlow = TOleEnum;
const
  eRender                               = $00000000;
  eCapture                              = $00000001;
  eAll                                  = $00000002;
  EDataFlow_enum_count                  = $00000003;
type
  ERole = TOleEnum;
const
  eConsole                              = $00000000;
  eMultimedia                           = $00000001;
  eCommunications                       = $00000002;
  ERole_enum_count                      = $00000003;
type
  IAudioEndpointVolumeCallback = interface(IUnknown)
  ['{657804FA-D6AD-4496-8A60-352752AF4F89}']
  end;
  IAudioEndpointVolume = interface(IUnknown)
  ['{5CDF2C82-841E-4546-9722-0CF74078229A}']
    function RegisterControlChangeNotify(AudioEndPtVol: IAudioEndpointVolumeCallback): Integer; stdcall;
    function UnregisterControlChangeNotify(AudioEndPtVol: IAudioEndpointVolumeCallback): Integer; stdcall;
    function GetChannelCount(out PInteger): Integer; stdcall;
    function SetMasterVolumeLevel(fLevelDB: single; pguidEventContext: PGUID): Integer; stdcall;
    function SetMasterVolumeLevelScalar(fLevelDB: single; pguidEventContext: PGUID): Integer; stdcall;
    function GetMasterVolumeLevel(out fLevelDB: single): Integer; stdcall;
    function GetMasterVolumeLevelScaler(out fLevelDB: single): Integer; stdcall;
    function SetChannelVolumeLevel(nChannel: Integer; fLevelDB: double; pguidEventContext: PGUID): Integer; stdcall;
    function SetChannelVolumeLevelScalar(nChannel: Integer; fLevelDB: double; pguidEventContext: PGUID): Integer; stdcall;
    function GetChannelVolumeLevel(nChannel: Integer; out fLevelDB: double): Integer; stdcall;
    function GetChannelVolumeLevelScalar(nChannel: Integer; out fLevel: double): Integer; stdcall;
    function SetMute(bMute: Boolean; pguidEventContext: PGUID): Integer; stdcall;
    function GetMute(out bMute: Boolean): Integer; stdcall;
    function GetVolumeStepInfo(pnStep: Integer; out pnStepCount: Integer): Integer; stdcall;
    function VolumeStepUp(pguidEventContext: PGUID): Integer; stdcall;
    function VolumeStepDown(pguidEventContext: PGUID): Integer; stdcall;
    function QueryHardwareSupport(out pdwHardwareSupportMask): Integer; stdcall;
    function GetVolumeRange(out pflVolumeMindB: double; out pflVolumeMaxdB: double; out pflVolumeIncrementdB: double): Integer; stdcall;
  end;
  IAudioMeterInformation = interface(IUnknown)
  ['{C02216F6-8C67-4B5B-9D00-D008E73E0064}']
  end;
  IPropertyStore = interface(IUnknown)
  end;
  IMMDevice = interface(IUnknown)
  ['{D666063F-1587-4E43-81F1-B948E807363F}']
    function Activate(const refId: TGUID;
                      dwClsCtx: DWORD;
                      pActivationParams: PInteger;
                      out pEndpointVolume: IAudioEndpointVolume): Hresult; stdCall;
    function OpenPropertyStore(stgmAccess: DWORD; out ppProperties: IPropertyStore): Hresult; stdcall;
    function GetId(out ppstrId: PLPWSTR): Hresult; stdcall;
    function GetState(out State: Integer): Hresult; stdcall;
  end;

  IMMDeviceCollection = interface(IUnknown)
  ['{0BD7A1BE-7A1A-44DB-8397-CC5392387B5E}']
  end;
  IMMNotificationClient = interface(IUnknown)
  ['{7991EEC9-7E89-4D85-8390-6C703CEC60C0}']
  end;
  IMMDeviceEnumerator = interface(IUnknown)
  ['{A95664D2-9614-4F35-A746-DE8DB63617E6}']
    function EnumAudioEndpoints(dataFlow: EDataFlow; deviceState: SYSUINT; DevCollection: IMMDeviceCollection): Hresult; stdcall;
    function GetDefaultAudioEndpoint(EDF: SYSUINT; ER: SYSUINT; out Dev :IMMDevice ): Hresult; stdcall;
    function GetDevice(pwstrId: pointer; out Dev: IMMDevice): HResult; stdcall;
    function RegisterEndpointNotificationCallback(pClient: IMMNotificationClient): Hresult; stdcall;
  end;
implementation
end.

///////////////////////
simple sample :)
///////////////////////

//...... other code

uses ... ActiveX, MMDevApi, ...;

//...... other code

var
  endpointVolume: IAudioEndpointVolume = nil;
procedure TForm1.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;
procedure TForm1.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;

/////////////////////////////////////

// with best regards ToxicDream