program Project1;

uses
  Windows, ...;

type
  TMP3 = class
  private
    pBaseFilter: IBaseFilter;
    pGraphBuilder:IGraphBuilder ;
    pMediaCtrl: IMediaControl;
    pMediaEvent: IMediaEventEx;
    ready: bool;
  public
    constructor Create;
    destructor Destroy; override;
    function Load(filename: string): BOOL;
    procedure Cleanup();

    procedure Play();
    procedure Pause();
    procedure Stop();
  end;

var
  MP3: TMP3;
  hWindow: HWND = 0;

constructor TMP3.Create;
begin
  pBaseFilter := nil;
  pGraphBuilder := nil;
  pMediaCtrl := nil;
  pMediaEvent := nil;

  ready := false;

  CoInitialize(nil);
end;

destructor TMP3.Destroy;
begin
  Cleanup;
end;

function TMP3.Load(filename: string): BOOL;
begin
  // ...
end;

procedure TMP3.Cleanup();
begin
  if pMediaCtrl <> nil then
  begin
    pMediaCtrl.Stop();
    pMediaCtrl._Release();
    pMediaCtrl := nil;
  end;

  if pBaseFilter <> nil then
  begin
    pBaseFilter._Release;
    pBaseFilter := nil;
  end;

  if pMediaEvent <> nil then
  begin
    pMediaEvent._Release();
    pMediaEvent := nil; // <--<< Boing #1
  end;

  if pGraphBuilder <> nil then
  begin
    pGraphBuilder._Release(); // <--<< Boing #2
    pGraphBuilder := nil;
  end;

  CoUninitialize();
end;

procedure TMP3.Play();

...

procedure TMP3.Stop();
begin
  if ready then pMediaCtrl.Stop();
end;

// --- Main ------------------------------------------------------------------

begin
  MP3:= TMP3.Create;
  try
    if MP3.Load('Nuppsy-SoulEye 128kbps.mp3') then
    begin
      MP3.Play;

      // MB_USERICON for a non BeepBox ;-)
      MessageBox(hWindow, 'Playing...', '!', MB_OK or MB_USERICON);

      // MP3.Stop; // "Autostop" im Destructor
    end;
  finally
    MP3.Free;
  end;
end.