程序代码：

  QAudioDevice defaultDevice = QMediaDevices::defaultAudioOutput();
  QAudioOutput * audioOutput = new QAudioOutput(defaultDevice);
  audioOutput->setVolume (0.1);
  QMediaPlayer * player = new QMediaPlayer();
  player->setAudioOutput (audioOutput);
  player->setSource (QUrl ("/music/那些年.mp3"));
  player->play ();