MediaPlayerElement在导航到另一帧后正在播放音频。如果我再次导航到此帧，我可以听到两个音频示例，一个来自当前播放视频的音频，另一个来自上次导航到此帧时的音频。如何在导航到另一帧后停止MediaPlayerElement？

供参考：

框架的XAML部分的完整代码

<Page.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="/Styles/MediaPlayerDictionary.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Page.Resources>
<Grid Background="Transparent">
    <MediaPlayerElement  Name="YoutubePlayer" MaxWidth="640" MaxHeight="360" AreTransportControlsEnabled="True">
        <MediaPlayerElement.TransportControls>
            <video:CustomMediaTransportControls x:Name="CustomMediaControl" IsSkipBackwardButtonVisible="True" IsSkipForwardButtonVisible="True" IsSkipBackwardEnabled="True" IsSkipForwardEnabled="True" IsFullWindowButtonVisible="True" IsFullWindowEnabled="True" QualityChanged="CustomMediaControl_QualityChangedAsync"/>
        </MediaPlayerElement.TransportControls>
    </MediaPlayerElement>
</Grid>

框架的C#部分的完整代码

public sealed partial class VideosPage : Page
{

public VideosPage()
{
    this.InitializeComponent();
}

protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
    base.OnNavigatingFrom(e);
    YoutubePlayer.MediaPlayer.Dispose();
}

public async Task setVideoSourceAsync(YouTubeQuality videoQuality)
{

    try
    {
        var youtubeUrl = await YouTube.GetVideoUriAsync("QTYVJhy04rs", YouTubeQuality.Quality144P, videoQuality);
        YoutubePlayer.Source = MediaSource.CreateFromUri(youtubeUrl.Uri);
        YoutubePlayer.AutoPlay = true;
    }
    catch (Exception e)
    {
        //await setVideoSourceAsync();
    }
}

private async void Page_LoadedAsync(object sender, RoutedEventArgs e)
{
    if (ApplicationView.GetForCurrentView().IsViewModeSupported(ApplicationViewMode.CompactOverlay))
    {
        CustomMediaControl.IsCompactOverlayButtonVisible = true;
    }
    await setVideoSourceAsync(YouTubeQuality.Quality360P);
}

private async void CustomMediaControl_QualityChangedAsync(object sender, QualityChangedEventArgs e)
{
    await setVideoSourceAsync(e.NewQuality);
}
}