Wp 8.1 Get duration of mp3 track

i would like to ask how i can get length of my audio file in app.

Im loading track like this

var installFolder = Windows.ApplicationModel.Package.Current.InstalledLocation;


        var resourcesFolder = await installFolder.GetFolderAsync("Resources");
        var mp3FilesFolder = await resourcesFolder.GetFolderAsync("mp3Files");


        var audioFile = await mp3FilesFolder.GetFileAsync("sound.mp3");
        var stream = await audioFile.OpenAsync(Windows.Storage.FileAccessMode.Read);



        mediaplayer.SetSource(stream, audioFile.ContentType);
        mediaplayer.Play();

but i dont know how to get the duration of track.

|Thanks