Techniques for WCAG 2.0

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SL12: Pausing, Stopping, or Playing Media in Silverlight MediaElements

Applicability

This technique relates to:

User Agent and Assistive Technology Support Notes

See User Agents Supported for general information on user agent support.

Description

The objective of this technique is to create a control user interface for the Silverlight MediaElement object. The controls enable users to pause or stop the video to prevent the video images on the MediaElement surface from moving, and stop video-associated audio. These UI controls enable an interaction defined in code event handlers. Each handler calls one of the following MediaElement methods:

Note that by default, a MediaElement will start playing its media as soon as the UI loads completely AND the media source file is downloaded (or a certain buffer size is reached, in the case of streaming media). Use the AutoPlay property to change this default.

Examples

Example 1: Providing MediaElement controls in the UI

This example has a UI definition in XAML and interaction logic in C#.

<UserControl x:Class="MediaElementControls.MainPage"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 >
  <Grid x:Name="LayoutRoot">
      <StackPanel>
          <MediaElement x:Name="media" Source="/xbox.wmv"
         Width="300" Height="300" 
         AutomationProperties.Name="Video of new Fable game for XBox"           
      />
          <Grid Name="UIControls">
              <Grid.ColumnDefinitions>
                  <ColumnDefinition Width="*" />
                  <ColumnDefinition Width="*" />
                  <ColumnDefinition Width="*"/>
              </Grid.ColumnDefinitions>
              <Grid.RowDefinitions>
                  <RowDefinition Height="*" />
                  <RowDefinition Height="Auto" />
                  <RowDefinition Height="20" />
              </Grid.RowDefinitions>
              <Button Click="StopMedia" 
   Grid.Column="0" Grid.Row="1" Content="Stop" />
              <Button Click="PauseMedia" 
   Grid.Column="1" Grid.Row="1" Content="Pause" />
              <Button Click="PlayMedia" 
   Grid.Column="2" Grid.Row="1" Content="Play" />
              <Button Click="MuteMedia" 
  Grid.Row="2" Grid.Column="0" Content="Mute" />
              <TextBlock Name="VolumeLabel" Grid.Row="2" Grid.Column="1" HorizontalAlignment="Right">Volume</TextBlock>
              <Slider Height="20"
          Value="{Binding Volume, Mode=TwoWay, ElementName=media}"
          Minimum="0" Maximum="1"
          Grid.Row="2" Grid.Column="2" Grid.ColumnSpan="2"
              AutomationProperties.LabeledBy="{Binding ElementName=VolumeLabel}"/>
          </Grid>
      </StackPanel>
  </Grid>
</UserControl>

private void StopMedia(object sender, RoutedEventArgs e)
{
    media.Stop();
}
private void PauseMedia(object sender, RoutedEventArgs e)
{
    media.Pause();
}
private void PlayMedia(object sender, RoutedEventArgs e)
{
    media.Play();
}
private void MuteMedia(object sender, RoutedEventArgs e)
{
    Button target = sender as Button;
    // mute if not muted, unmute if already muted, in either case make sure the button content for text and accessibility info is updated
    if (!media.IsMuted)
    {
        media.IsMuted = true;
        target.Content = "Unmute";
    }
    else
    {
         media.IsMuted = false;
         target.Content = "Mute";
     }
}

This example is shown in operation in the working example of Media Element Controls.

Resources

Resources are for information purposes only, no endorsement implied.

Tests

Procedure

  1. Using a browser that supports Silverlight, open an HTML page that references a Silverlight application through an object tag. The application is expected to incorporate a MediaElement in the user interface.

  2. Check that interactive controls are available so that users can pause or stop the media.

  3. Check that when activated, the controls stop or pause the media.

Expected Results

#2 and #3 are 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.

Techniques are Informative

Techniques are informative—that means they are not required. The basis for determining conformance to WCAG 2.0 is the success criteria from the WCAG 2.0 standard—not the techniques. For important information about techniques, please see the Understanding Techniques for WCAG Success Criteria section of Understanding WCAG 2.0.