Accessing Alternate Audio Tracks in Silverlight Media

Example 1: Changing AudioStreamIndex

This example has a UI definition in XAML and interaction logic in C#. In addition to the typical Play/Pause/Stop controls, this interface includes a Play Full-Description Audio button. Activating the button invokes a function that swaps the audio channels and plays an alternative synchronized audio channel that contains a composite full-description audio track.

The following is the basic UI in XAML. This example is deliberately simple and does not include AutomationProperties. Audio streams are identified by an index in a collection.

      <Grid x:Name="LayoutRoot" Background="White">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
            <RowDefinition Height="20" />
        </Grid.RowDefinitions>
        <MediaElement x:Name="media" Source="/combined.wmv"
           Width="300" Height="300" 
           Grid.Column="0" Grid.Row="0" Grid.ColumnSpan="3"
           AutoPlay="false"
        />
        <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 Name="AltAudioBtn" Grid.Row="2" HorizontalAlignment="Left" Grid.ColumnSpan="2" 
        Click="AltAudioBtn_Click">Play Full-Description Audio</Button>
    </Grid>

The following is the C# logic.

        private void AltAudioBtn_Click(object sender, RoutedEventArgs e)
        {
            if (media.AudioStreamCount > 1)
            {
                if (media.AudioStreamIndex == 1)
                {
                    media.AudioStreamIndex = 0;
                    (sender as Button).Content = "Play full-description audio";
                } else {
                    media.AudioStreamIndex = 1;
                   (sender as Button).Content = "Play default audio";
                }
            }
            else
            {
                (sender as Control).IsEnabled = false;
            }
        }
        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();
        }

This example is shown in operation in the working example of Alternative Audio Channel. If using the test file, the test contains test audio tones rather than actual audio description, but the pitch of the tones is indicative of which of the channels is selected and played.