如何在WPF中将视频用作媒体元素背景？

Question

我是WPF的初学者，在我创建的一个小程序中，有一个带有视频作为背景的窗口。

我使用了媒体元素，该视频上方还有其他内容。它可以在我单独进行的测试窗口中完美运行，但不在这里。我只是得到普通的背景。我浏览了media元素上的指南，但仍然找不到问题...

<Window x:Class="GlorifiedWallpaperApp.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:GlorifiedWallpaperApp"
    mc:Ignorable="d"
    ResizeMode="NoResize"
    WindowState="Normal"
    WindowStyle="None"
    AllowsTransparency="True"
    WindowStartupLocation="CenterScreen"
    Title="LoginPage" Height="720" Width="1280">

<WindowChrome.WindowChrome>
    <WindowChrome CaptionHeight="27"/>
</WindowChrome.WindowChrome>

<Grid FocusManager.FocusedElement="{Binding ElementName=passBox}">

    <!--Definitions-->
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="100"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="100"/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="100"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="100"/>
    </Grid.RowDefinitions>


    <!--BACKGROUND VIDEO-->
    <MediaElement Source="/Resources/lensEffect.wmv"
                  Grid.Column="0" Grid.Row="0"
                  Grid.ColumnSpan="9" Grid.RowSpan="5"
                  x:Name="Lens_Effect"
                  MediaEnded="MediaElement_MediaEnded"
                  LoadedBehavior="Play" />

    <Rectangle Grid.Column="0" Grid.Row="0"
               Grid.ColumnSpan="9" Grid.RowSpan="5"
               Fill="Black" Opacity="0">
    </Rectangle>

    <!--ENTER PIN TEXT-->
    <TextBlock Foreground="White"
               Grid.Column="3" Grid.Row="4"
               Grid.ColumnSpan="3"
               HorizontalAlignment="Center"
               VerticalAlignment="Center"
               Margin="0,0,0,50"
               FontSize="15" FontFamily="Courier New"
               Opacity=".3">
        <TextBlock.Text>
            enter the pin above. i'm waiting...
        </TextBlock.Text>
    </TextBlock>

    <!--EXIT BUTTON-->
    <Button Grid.Column="0" Grid.Row="0"
            Background="Transparent"
            x:Name="Exit_Button"
            BorderBrush="Transparent"
            MaxHeight="40"
            MaxWidth="40" Opacity=".5"
            Click="Exit_Button_Click"
            Style="{StaticResource buttonLogin}">
        <Image Source="/Resources/LoginExitButton.png"/>
    </Button>

    <!--BGTextBox-->
    <PasswordBox x:Name="passBox" Grid.Row="1" Grid.Column="0"
             Grid.RowSpan="3" Grid.ColumnSpan="9"
             Margin="0,0,0,0" MaxWidth="1000"
             Background="Transparent" Foreground="#63ffdd"
             BorderBrush="Transparent" 
             HorizontalContentAlignment="Center"
             VerticalContentAlignment="Top"
             Opacity=".4" FontSize="400" MaxLength="6"
             PasswordChar="•" Style="{StaticResource passwordFocusRemoval}">
        <PasswordBox.InputBindings>
            <KeyBinding Key="Return" Command="{Binding }" />
        </PasswordBox.InputBindings>
    </PasswordBox>

    <!--MAIN LOGO-->
    <Button Grid.Column="3" Grid.Row="1"
            Grid.RowSpan="3" Grid.ColumnSpan="3"
            Margin="0,0,0,50"
            x:Name="Login_Logo" MaxHeight="170"
            Style="{StaticResource buttonLogin}"
            Click="Login_Logo_Click">
        <Image Source="/Resources/LoginLogo.png"/>
    </Button>

及其背后的代码：

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

    }

    Collection myCollection = new Collection();

    private void MediaElement_MediaEnded(object sender, RoutedEventArgs e)
    {
        Lens_Effect.Position = TimeSpan.FromMilliseconds(1);
    }

    private void keyUp(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.OemComma)
            MessageBox.Show("YAY!!!");
    }

    public void Exit_Button_Click(object sender, RoutedEventArgs e)
    {
        System.Diagnostics.Process.GetCurrentProcess().Kill();
    }

    private void Login_Logo_Click(object sender, RoutedEventArgs e)
    {
        if (passBox.Password == "key")
        {
            myCollection.Show();
            this.Close();
        }
    }

}