MCI 调整音量

var
  P: MCI_DGV_SETAUDIO_PARMS;
  P.dwCallback := 0;
  P.dwItem := MCI_DGV_SETAUDIO_VOLUME;
  P.dwValue := vol;//要设置的音量
  P.dwOver := 0;
  P.lpstrAlgorithm := nil;
  P.lpstrQuality := nil;
  mciSendCommand(MediaPlayer1.DeviceID, MCI_SETAUDIO,
    MCI_DGV_SETAUDIO_VALUE or MCI_DGV_SETAUDIO_ITEM, Cardinal(@P));