Qt QMediaPlayer：媒体处于未知状态

我创建了一个QMediaPlayer，将视频地址传递给它，但它不会播放。我检查了mediaStatus和player状态，它们始终保持0。基本思想是：

QMediaPlayer player = new QMediaPlayer();
cout << player.mediaStatus(); // should print 1: NoMedia but is 0: UnknownMediaStatus

player.setVideoOutput(some_constructed_video_widget);
cout << player.mediaStatus(); // should print 1: NoMedia but is 0: UnknownMediaStatus

player.setMedia(QUrl::fromLocalFile("path/to/test/video/test.mp4"));
cout << player.mediaStatus(); // should print 2: LoadingMedia but is 0: UnknownMediaStatus

player.play();
cout << player.mediaStatus(); // should print 3: LoadedMedia but is 0: UnknownMediaStatus
                              // and of course, no video gets played

---

我使用的是Mac 10.9和Qt 5.3.0，但我认为Mac/Qt版本与此问题无关。

@ddriver Nope。。。我在mac 10.9上，为未来用户使用Qt 5.3.0：首先确保您的pro文件中有此文件：Qt+=多媒体QTPLUGIN+=qavfmediaplayer如果是，那么您得到的输出是因为QtMultimedia找不到与您的平台相关联的多媒体后端。您可以根据平台查看后端列表。请安装并重试。我在Linux上使用Qt5时遇到了这个问题，我需要安装gstreamer后端。

int main(int argc, char *argv[])
{
    QMediaPlayer * temp = new QMediaPlayer(0, QMediaPlayer::VideoSurface);
    std::cout << "Constructed: " << temp->mediaStatus() << std::endl;
    temp->setMedia(QUrl::fromLocalFile("path/to/video/test.mp4"));
    std::cout << "SetMedia: " << temp->mediaStatus() << std::endl;
    temp->play();
    std::cout << "Play: " << temp->mediaStatus() << std::endl;
-> debug breakpoint here
    ......
}

defaultServiceProvider::requestService(): no service found for - "org.qt-project.qt.mediaplayer"
Constructed: 0
SetMedia: 0
Play: 0