unable to run video in WPF - wpf

Question

I try to implement a video in WPF. The video is visible in Visual Studio (so I think the path is correct) but isn't visible (I also hear nothing) while I run the program. I have 1 MediaElement to implement the video and 3 Buttons (Play, Pause, Mute) below. The Build-Property of the video is "Resource".
XAML-Code:
<StackPanel HorizontalAlignment="Center" Width="340" Height="300" Margin="281,63,0,0" VerticalAlignment="Center">
<MediaElement Name="myMedia" Source="testvideo.wmv" LoadedBehavior="Manual" Width="320" Height="240" />
<StackPanel Orientation="Horizontal" Margin="0, 10, 0, 0">
<Button Content="Play" Margin="0, 0, 10, 0" Padding="5" Click="mediaPlay"/>
<Button Content="Pause" Margin="0, 0, 10, 0" Padding="5" Click="mediaPause"/>
<Button x:Name="muteButt" Content="Mute" Padding="5" Click="mediaMute"/>
</StackPanel>
</StackPanel>
Code Behind:
public MainWindow()
{
InitializeComponent();
myMedia.Volume = 100;
myMedia.Play();
myMedia.Position = new TimeSpan(0, 0, 5); // first frame 5 seconds
}
void mediaPlay(Object sender, EventArgs e)
{
myMedia.Play();
}
void mediaPause(Object sender, EventArgs e)
{
myMedia.Pause();
}
void mediaMute(Object sender, EventArgs e)
{
if (myMedia.Volume == 100)
{
myMedia.Volume = 0;
muteButt.Content = "Listen";
}
else
{
myMedia.Volume = 100;
muteButt.Content = "Mute";
}
}

Answer 1

I found my problem:
I had to set the property "Source" of the MediaElement in the code behind again. I don't know why, but now it works!