qt4 - 歌のメタ情報をフォノンで抽出する

Question

C ++でフォノンライブラリを使用して音楽プレーヤーを構築しています。これは、曲のメタ情報を抽出するためのコードです。

void MainWindow::metaStateChanged(Phonon::State newState, Phonon::State /* oldState */)
{
    if (newState == Phonon::ErrorState) {
        QMessageBox::warning(this, tr("Error opening files"),
            metaInformationResolver->errorString());
        while (!sources.isEmpty() &&
               !(sources.takeLast() == metaInformationResolver->currentSource())) {}  /* loop */;
        return;
    }

    if (newState != Phonon::StoppedState && newState != Phonon::PausedState)
        return;

    if (metaInformationResolver->currentSource().type() == Phonon::MediaSource::Invalid)
            return;

    QMap<QString, QString> metaData = metaInformationResolver->metaData();

    QString title = metaData.value("TITLE");
    if (title == "")
        title = metaInformationResolver->currentSource().fileName();

    QTableWidgetItem *titleItem = new QTableWidgetItem(title);
    titleItem->setFlags(titleItem->flags() ^ Qt::ItemIsEditable);
    QTableWidgetItem *artistItem = new QTableWidgetItem(metaData.value("ARTIST"));
    artistItem->setFlags(artistItem->flags() ^ Qt::ItemIsEditable);
    QTableWidgetItem *albumItem = new QTableWidgetItem(metaData.value("ALBUM"));
    albumItem->setFlags(albumItem->flags() ^ Qt::ItemIsEditable);
    QTableWidgetItem *yearItem = new QTableWidgetItem(metaData.value("DATE"));
    yearItem->setFlags(yearItem->flags() ^ Qt::ItemIsEditable);

    int currentRow = musicTable->rowCount();
    musicTable->insertRow(currentRow);
    musicTable->setItem(currentRow, 0, titleItem);
    musicTable->setItem(currentRow, 1, artistItem);
    musicTable->setItem(currentRow, 2, albumItem);
    musicTable->setItem(currentRow, 3, yearItem);

    if (musicTable->selectedItems().isEmpty()) {
        musicTable->selectRow(0);
        mediaObject->setCurrentSource(metaInformationResolver->currentSource());
    }

    Phonon::MediaSource source = metaInformationResolver->currentSource();
    int index = sources.indexOf(metaInformationResolver->currentSource()) + 1;
    if (sources.size() > index) {
        metaInformationResolver->setCurrentSource(sources.at(index));
    }
    else {
        musicTable->resizeColumnsToContents();
        if (musicTable->columnWidth(0) > 300)
            musicTable->setColumnWidth(0, 300);
    }
}

ただし、これは情報の抽出に失敗しています。さらにコードを投稿する場合はお知らせください。