See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.0 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.0.
Microsoft Silverlight, versions 3 and greater
Silverlight managed programming model and Silverlight XAML
This technique relates to:
See User Agent Support Notes for SL16. Also see Silverlight Technology Notes.
The objective of this technique is to use text captioning that is
embedded in the stream with media displayed in a Silverlight MediaElement,
and present that text captioning in a separate Silverlight control
or text element.
This particular technique uses scripting files with a TimelineMarkers collection
that are embedded directly within the media file. When text captioning
is embedded directly in the streams, synchonization of the scripting
stream versus the video content stream is done automatically by the MediaElement component.
Each time the MarkerReached event fires, that is an
indication that a synch point in the video that corresponds to a script
marker entry has been reached. Silverlight application authors can
obtain the text from the relevant timeline marker entry through their
event handler implementations, and can display captions in the user
interface area where the text captions are displayed. Typical Silverlight
controls that can be used for displaying text captions include TextBlock (nonfocusable), TextBox,
or RichTextBox. A typical interface design would place
the caption-display control in close proximity to the MediaElement control
that is being captioned, for example might place the captions directly
underneath the MediaElement "screen".
Script-embedded captions are captions that are stored directly in the media file as metadata, rather than as a separate file. For information about techniques for captions in separate files, see SL28: Using Separate Text-Format Text Captions for MediaElement Content.
Producing the media file with TimelineMarkers captions
directly in embedded scripting can be accomplished using the Microsoft
Expression Encoder tool. Online help for the procedure of encoding
scripting with text captions in the stream are available in the offline
Help file that installs with the Microsoft Expression 4 Encoder products.
For more information, see Expression
Encoder Pro Overview.
There is a public
API for introducing Markers into a WMV file, as part of the Windows
Media Format SDK. Using Expression Encoder is the way that the task
of directly embedding TimelineMarkers is presented
and taught in Microsoft's available instructional material on Silverlight.
However, because the mechanism is public, it is possible that other
tools exist or will exist that can also produce media with script-encoded TimelineMarkers.
This example has a UI definition in XAML and interaction logic in
C#. The following is the basic UI in XAML. This example is deliberately
simple and does not include AutomationProperties for
identification or user instructions. The most relevant part of this
example is that the Silverlight author declares a handler for the event MarkerReached.
This event fires potentially hundreds of times, once for each caption
in the stream. Each time the event fires, the event handler runs and
adds the text to the dedicated TextBox in the user
interface.
<UserControl x:Class="MediaTimelineMarkers.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
>
<StackPanel x:Name="LayoutRoot" Background="White">
<MediaElement MarkerReached="OnMarkerReached"
HorizontalAlignment="Left"
Source="/spacetime.wmv"
Width="300" Height="200" />
<ScrollViewer>
<TextBox Name="captionText" Height="40"
IsReadOnly="true" AcceptsReturn="true"/>
</ScrollViewer>
</StackPanel>
</UserControl>
private void OnMarkerReached(object sender, TimelineMarkerRoutedEventArgs e)
{
captionText.Focus();
captionText.SelectedText = e.Marker.Text.ToString() + "\n";
}
This example is shown in operation in the working example of Media Timeline Markers.
Resources are for information purposes only, no endorsement implied.
Accessible Media Project - a reference implementation MediaPlayer control from the Silverlight product team that includes several accessibility features including captioning; note that the codebase might not be updated to Silverlight version 4
Using a browser that supports Silverlight, open an HTML page that references a Silverlight application through an object tag. The application plays media that is expected to have text captioning.
Check that a text area in the user interface shows captions for the media.
# 2 is true.
If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.