The cd may or may not have a serial number and/or Universal Product Code embedded in the cd. The MCI Windows extension does provide this functionality through the MCI_INFO_MEDIA_IDENTITY command. This command will return a unique ID string consisting of 6 hexadecimal digits. Example:

uses MMSystem, MPlayer;
procedure TForm .Button Click(Sender: TObject);
var
  mp : TMediaPlayer;
  msp : TMCI_INFO_PARMS;
  MediaString : array[0..255] of char;
  ret : longint;
begin
  mp := TMediaPlayer.Create(nil);
  mp.Visible := false;
  mp.Parent := Application.MainForm;
  mp.Shareable := true;
  mp.DeviceType := dtCDAudio;
  mp.FileName := 'D:';
  mp.Open;
  Application.ProcessMessages;
  FillChar(MediaString, sizeof(MediaString), #0);
  FillChar(msp, sizeof(msp), #0);
  msp.lpstrReturn := @MediaString;
  msp.dwRetSize := 255;
  ret := mciSendCommand(Mp.DeviceId,
                        MCI_INFO,
                        MCI_INFO_MEDIA_IDENTITY,
                        longint(@msp));
  if Ret <> 0 then begin
   MciGetErrorString(ret, @MediaString, sizeof(MediaString));
   Memo .Lines.Add(StrPas(MediaString));
  end else
    Memo .Lines.Add(StrPas(MediaString));
  mp.Close;
  Application.ProcessMessages;
  mp.free;
end;
end.