为什么MediaElement在通话时间不起作用？

Question

我的WPF应用程序中有一些MediaElements

如果我调用Question1_5.Play();，则Timer_activated.Play();不能按时播放（该音频在调用Play（）方法后播放5-6秒）。

出什么问题了？

        private void NewGame_MouseLeftButtonDown(object sender, 
        MouseButtonEventArgs e) {
        Dispatcher.BeginInvoke((Action)(() => Windows.SelectedItem = Game));
        Questions1_5.Play();
        sb = FindResource("TimerAppear") as Storyboard;
        sb.Begin();
        sb.Pause();
        timer = new DispatcherTimer();
        timer.Tick += new EventHandler(timer_Tick);
        timer.Interval = new TimeSpan(0, 0, 4);
        timer.Start();
    }

    private void timer_Tick(object sender, EventArgs e) {
        Timer_activated.Play();
        sb.Resume();
        sb = FindResource("Seconds15") as Storyboard;
        timer.Stop();
    }