QMediaPlayer setVolume() does not work

1. Create a new project with "QT Widget Application"
2. Add a pushbutton
3. in the pushbutton's onclick function, write:

void MainWindow::on_pushButton_clicked()

{ player->setMedia(QUrl("qrc:/bgm/Summer.wav")); player->setVolume(1); // nothing happened player->play(); // plays normally player->setMuted(true); // nothing happened }

4. Build and run.
5. You'll notice that the setVolume(1) function and setMuted(true) function make no effect at all.
6. I tried changing the setMedia()'s source from a local file, no use.
7. I also tried change my system sound device from my USB Adam Artist 5 to mac mini's built-in speaker... and everything just went on the same way.
8. There are 4 sound devices on my OS X system:
1)build-in spaker
2)ASUS PA238(because this ASUS monitor has got an HDMI)
3)USB Audio DAC(my USB Adam Artist 5)
4)"System Sound"(from a software that can record real-time screen from both my mac mini and my iPad. This software creates a "virtual" sound card. I think you may want to test this.)