MediaElement Stream and VisualBrush

Question

From a WCF Service I got a videostream. Now I want to show this videostream in a MediaElement inside of a VisualBrush.

I tried giving the URI directly, this doesn't work. So I wrote a simple Converter that saves the video to HDD and returns the URI to saved file. Here is my code.

The Converter:

[ValueConversion(typeof(Stream), typeof(Uri))]
public class MediaElementStreamConverter : IValueConverter {
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
        if (!(value is Stream)) {
            return new Uri("");
        }
        string path = Path.GetTempFileName();
        using (var fs = new FileStream(path, FileMode.OpenOrCreate)) {
            ((Stream)value).CopyTo(fs);
        }
        return path;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
        return "";
    }
}

And here is the code where I use the Converter:

<Grid Opacity="0.4" VerticalAlignment="Top">
    <Grid.Background>
        <VisualBrush>
            <VisualBrush.Visual>
                <MediaElement IsMuted="True" ScrubbingEnabled="True" LoadedBehavior="Manual" Source="{Binding stream, Converter={StaticResource MediaElementStreamConverter}}" Loaded="MediaElement_VideoDataTemplate_Loaded" />
            </VisualBrush.Visual>
        </VisualBrush>
    </Grid.Background>
</Grid>

And here is the MediaElement_VideoDataTemplate_Loaded method:

private void MediaElement_VideoDataTemplate_Loaded(object sender, RoutedEventArgs e) {
    var mediaElement = (MediaElement)sender;
    mediaElement.Play();
    mediaElement.Pause();
}

The problem is, the video don't starts.