Strange problem with RenderTargetBitmap

I am developing a frame extract from video program.  It works well and I can set an interval for the screenshots which are the stored in individual jpg files.

Now I am adding the ability to add things like titles to those jpgs.  I have an architecture which creates a TitleEffect which has things like the text, fontsize, color and a in/out point.  Now comes the problem.

My first go round is basically - if there is an effect on the video I am extracting frames from then it calls a function within the TitleEffect class which checks the in/out time and if the position of the video falls within those times it returns a usercontrol which can be added to the children of  the Grid which I am using as the basis for the screen capture.  Again this works well and I can see the title appear when it should and disappear when it should.

Now the problem.  While I can see the title in the window showing the video while doing the frame captures, the resulting jpg does not show the title.  If I put the usercontrol into my window thru XAML and rather than add the control in code just set the datacontext, again I see the title and the jpg shows the title.

I have used Snoop to look at the visual tree and both methods result in the same entries in the tree.

The reason I am trying to do it the code way is that I want to be able to have many different types of effects all using the same architecture.  With the present problem that is not feasible.

The code I am using to add the usercontrol in code is:

        If currentFileBeingCaptured.Effects.Count > 0 Then

            Dim af As AddedEffect = CType(currentFileBeingCaptured.Effects(0), AddedEffect)
            Dim tmp As UserControl = af.GetUIElement(theMediaPlayer.Position)
            If tmp IsNot Nothing Then
                If Not useCurrent Then
                    If OverLayGrid.Children.Count > 0 Then
                        OverLayGrid.Children.RemoveAt(0)
                    End If
                    tmp.DataContext = af
                    OverLayGrid.Children.Add(tmp)
                Else
                    testUC.DataContext = af
                End If
                overlayadded = True
            End If
        End If

In the above code useCurrent is a variable I created just for testing.  True uses the control already existing in the XAML and false will take the usercontrol passed back from the GetUIElement.  If I am using the generated usercontrol I check the count of children in the grid named OverLayGrid and if it is larger than zero (the XAML based usercontrol) it removes it.

As I said above the resulting visual tree is identical in both cases with the only difference being that the XAML based usercontrol has a name.

Any help would be great as I have tried about every permutation I can think of to fix this problem but none has worked.

TIA

Lloyd Sheen

  BTW the XAML for the VisualGrid is:

<Grid x:Name="VisualGrid" Grid.Row="1"
                          Width="{Binding ElementName=sizeCombo, Path=SelectedItem.width, Converter={StaticResource dummyConverter}}" 
                          Height="{Binding ElementName=sizeCombo, Path=SelectedItem.height, Converter={StaticResource dummyConverter}}"><MediaElement x:Name="theMediaPlayer" ScrubbingEnabled="True" 
                              Visibility="Visible" 
                              LoadedBehavior="Manual" 
                              Loaded="MediaElement_Loaded"  
                              MediaOpened="theMediaPlayer_MediaOpened" 
                              Margin="0,5"></MediaElement><Grid x:Name="OverLayGrid"><local:TitleEffectUC x:Name="testUC" Visibility="Visible"></local:TitleEffectUC></Grid></Grid>

Lloyd Sheen