As this is an audio, we don't need a QVideoWidget. So we can do:
_player = new QMediaPlayer(this);
QUrl file = QUrl::fromLocalFile(QFileDialog::getOpenFileName(this, tr("Open Music"), "", tr("")));
if (file.url() == "")
return ;
_player->setMedia(file);
_player->setVolume(50);
_player->play();
in the .h:
QMediaPlayer *_player;
this will open a dialog where you can choose your music and it will play it.