connect(mediaObject, SIGNAL(tick(qint64)), this, SLOT(tick(qint64))); connect(mediaObject, SIGNAL(stateChanged(Phonon::State,Phonon::State)), this, SLOT(stateChanged(Phonon::State,Phonon::State))); connect(metaInformationResolver, SIGNAL(stateChanged(Phonon::State,Phonon::State)), this, SLOT(metaStateChanged(Phonon::State,Phonon::State))); connect(mediaObject, SIGNAL(currentSourceChanged(Phonon::MediaSource)), this, SLOT(sourceChanged(Phonon::MediaSource))); connect(mediaObject, SIGNAL(aboutToFinish()), this, SLOT(aboutToFinish()));1.mediaObject类主要提供一个能够处理媒体播放的介面。这个怎么理解?2.上面五个信号,都是干嘛的?