Use the WriteableBitmap class to update and render a bitmap on a per-frame basis. This is useful for taking snapshots of playing video, generating algorithmic content, such as a fractal image, and for data visualization, such as a music visualizing application.

You can use this class's constructor to render a bitmap or, if you want to render the bitmap multiple times, use the Render method. If you use the Render method, you will need to call Invalidate in order for the bitmap to render.

When assigning colors to pixels in your bitmap, use pre-multiplied colors.

Note:
WriteableBitmap does not render popup controls such as Popup, ComboBox and ToolTip.

The following example demonstrates how to use a WriteableBitmap to take snapshots of a playing video and display those snapshots as thumbnails. Click on the video as it plays to create the thumbnails.

Run this sample

<StackPanel Orientation="Vertical" HorizontalAlignment="Stretch" Margin="10">

    <Border BorderBrush="AntiqueWhite" BorderThickness="2" CornerRadius="1" Margin="4" 
  HorizontalAlignment="Center" VerticalAlignment="Top">
        <Border>
            <MediaElement x:Name="myMediaElement" Source="xbox.wmv" Stretch="None" MouseLeftButtonDown="me_MouseLeftButtonDown"/>
        </Border>
    </Border>

    <!-- thumbnails go here -->
    <StackPanel x:Name="thumbs" Orientation="Horizontal" Margin="10,40,10,10">
    </StackPanel>

</StackPanel>

private void me_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{

    // Create a WriteableBitmap and set it to the MediaElement (video).
    // The WriteableBitmap represents a "snapshot" of the video.
    WriteableBitmap wb = new WriteableBitmap(myMediaElement, null);

    // Create an image of the desired size and set its source to
    // the WriteableBitmap representing a snapshot of the video.
    Image image = new Image();
    image.Height = 64;
    image.Margin = new Thickness(10);
    image.Source = wb;

    // Display the snapshot of the video among the thumbnails. 
    thumbs.Children.Add(image);
}

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Reference