HowTo: Hide Video area of Silverlight Media Framework Player

Since our onoing project ClipFlair is a follow-up of the succesful project LeViS, during its development I’m also looking at covering possible use-cases I infer from feedback entries at LvS application issue tracker on Codeplex (note that ClipFlair is also opensourced on Codeplex at http://ClipFlair.codeplex.com).

One such issue (http://lvs.codeplex.com/workitem/11511) was titled “Allow video hiding while controller is visible for audio only”, so since Silverlight Media Framework (SMF) is used for the media player in ClipFlair, I looked into how to tell it to hide the video area.

Well, it seems that to hide the video and hear just the audio in SMFPlayer one needs to set MediaPresenterElement‘s (a property of SMFPlayer class) MaxWidth and MaxHeight to 0. One can do that at an overriden OnApplyTemplate method in a class descding from SMFPlayer, or could also do it at a custom SMF player template.

Note that setting MediaPresenterElement’s Visibility property to Visibility.Collapsed makes the player not load the video at all, so that one was not an option.

One could define a VideoVisible DependencyProperty at a class descending from SMFPlayer:

    #region VideoVisible

    /// <summary>
    /// VideoVisible Dependency Property
    /// </summary>
    public static readonly DependencyProperty VideoVisibleProperty =
        DependencyProperty.Register("VideoVisible", typeof(bool), 
            typeof(MediaPlayer),
            new FrameworkPropertyMetadata(false,
                FrameworkPropertyMetadataOptions.None,
                new PropertyChangedCallback(OnVideoVisibleChanged)));

    /// <summary>
    /// Gets or sets the VideoVisible property.
    /// </summary>
    public bool VideoVisible
    {
      get { return (bool)GetValue(VideoVisibleProperty); }
      set { SetValue(VideoVisibleProperty, value); }
    }

    /// <summary>
    /// Handles changes to the VideoVisible property.
    /// </summary>
    private static void OnVideoVisibleChanged(DependencyObject d, 
                                         DependencyPropertyChangedEventArgs e)
    {
      MediaPlayer target = (MediaPlayer)d;
      bool oldVideoVisible = (bool)e.OldValue;
      bool newVideoVisible = target.VideoVisible;
      target.OnVideoVisibleChanged(oldVideoVisible, newVideoVisible);
    }

    /// <summary>
    /// Provides derived classes an opportunity to handle changes to the 
    /// VideoVisible property.
    /// </summary>
    protected virtual void OnVideoVisibleChanged(bool oldVideoVisible, 
                                                 bool newVideoVisible)
    {
      MediaPresenterElement.MaxWidth = (newVideoVisible)? 
                                             double.PositiveInfinity : 0;
      MediaPresenterElement.MaxHeight = (newVideoVisible) ? 
                                             double.PositiveInfinity : 0;
    }

    #endregion

 

At first, to restore the MaxWidth/MaxHeight to show the video area again I tried to set them to double.NaN which didn’t work. Then I checked MaxWidth documentation which was saying:

The maximum width of the element, in device-independent units (1/96th inch per unit). The default value is PositiveInfinity. This value can be any value equal to or greater than 0.0. PositiveInfinity is also valid.

and

String representation of a Double value equal to or greater than 0.0. This is interpreted as a device-independent unit (1/96th inch) measurement. Strings need not explicitly include decimal points. For instance a value of 1 is acceptable.

The same Double range restrictions as mentioned in the Property Value section apply, except that you must use x:Static Markup Extension to set the value to be PositiveInfinity.

Per the 1st quote, one just needs to set MaxWidth or MaxHeight to double.PositiveInfinity (and not double.NaN that I originally expected) to reset it to its default value, that is behave as if a maximum width or height respectively has never been set.

As for the second quote, it basically says that XAML double fields need special treatment in order to specify a positive infinity value (if you ever need to, since you’d usually just skip the MaxWidth/MaxHeight field, unless you need to override some non-default inherited value). You would need to define a XAML namespace to point to the System namespace at mscorlib assembly (library), either at the root control in the XAML or directly where you need it:

<MyNameSpace:MyControl

      xmlns:sys="clr-namespace:System;assembly=mscorlib"

      MaxWidth=”{x:Static sys:Double.PositiveInfinity}”

      MaxHeight=”{x:Static sys:Double.PositiveInfinity}”

      …

/>

BTW, to hide the controller bar (called ControlStrip in SMF) you just set IsControlStripVisible property to false.