void MainWindow::onMultitrackDurationChanged()
{
    if (MLT.producer() && (void*) MLT.producer()->get_producer() == (void*) multitrack()->get_producer())
        m_player->onDurationChanged();
}
void MainWindow::onMultitrackDurationChanged()
{
    if (MLT.producer() && (void*) MLT.producer()->get_producer() == (void*) multitrack()->get_producer())
        m_player->onDurationChanged();
}