I figured out how to get my overlay to work on my DirectShow video. I just made a QPixmap of size 5x5 and put this on a QLabel of size 5x5 which I draw on top of the QAxWidget displaying my video. This works great instead of trying to create a transparent pixmap/label but I get a lot of flicker when I click on the video to draw the point. In my GUI building function I set these variables up like this:

Qt Code: 
  1. mpOverlay = new QPixmap( 5, 5 );
  2.    mpOverlay->fill( Qt::red );
  3.  
  4.    mpOverlayLabel = new QLabel( mpVideoPlayer );
  5.    mpOverlayLabel->setGeometry( QRect( 0, 0, 5, 5 ) );
  6.    mpOverlayLabel->hide( );
  7.    mpOverlayLabel->setPixmap( *mpOverlay );
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Then whenever I click on the screen I do this:

Qt Code: 
  1. if( event->type() == QEvent::MouseButtonRelease )
  2.       { 
  3.          AzElPoint point;
  4.          QMouseEvent *mouseEvent = static_cast<QMouseEvent *>(event);
  5.  
  6.          point.frameNumber = getCurrentFrame( );
  7.          point.xPos = mouseEvent->x( );
  8.          point.yPos = mouseEvent->y( ); 
  9.  
  10.          if( mouseEvent->button() == Qt::LeftButton )
  11.          {
  12.             // If left button, place mark on overlay to indicate position
  13.             // and store position in array at the current frame index
  14.             for( int i = 0 ; i < azElPoints.size( ) ; i++ )
  15.             {
  16.                if( azElPoints[i].frameNumber == getCurrentFrame( ) )
  17.                {
  18.                   azElPoints.removeAt( i );
  19.                   erasePoint = true;
  20.                }
  21.             }
  22.             azElPoints.push_back( point );
  23.             printf( "x=%d, y=%d\n", point.xPos, point.yPos );
  24.             update( );
  25.             return true;
  26.          }
  27.       }
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And my paint event handler just calls repaintWindow( ) which looks like this:

Qt Code: 
  1. void VideoViewerWindow::repaintWindow( )
  2. {
  3.    long lWidth, lHeight; 
  4.    HRESULT hr = pWindowlessControl->GetNativeVideoSize( &lWidth, &lHeight, NULL, NULL ); 
  5.    RECT rcSrc, rcDest; 
  6.    // Set the source rectangle.
  7.    SetRect( &rcSrc, 0, 0, lWidth, lHeight ); 
  8.  
  9.    // Get the window client area.
  10.    GetClientRect( (HWND) mpVideoPlayer->winId( ), &rcDest ); 
  11.    // Set the destination rectangle.
  12.    SetRect(&rcDest, 1, 1, 558, 349); 
  13.  
  14.    // Set the video position.
  15.    hr = pWindowlessControl->SetVideoPosition( &rcSrc, &rcDest ); 
  16.  
  17.    PAINTSTRUCT ps; 
  18.    HDC hdc; 
  19.    RECT rcClient;
  20.    GetClientRect( (HWND) mpVideoPlayer->winId( ), &rcClient ); 
  21.    hdc = BeginPaint( (HWND) mpVideoPlayer->winId( ), &ps ); 
  22.    if( pWindowlessControl != NULL ) 
  23.    { 
  24.       // Find the region where the application can paint by subtracting 
  25.       // the video destination rectangle from the client area.
  26.       // (Assume that g_rcDest was calculated previously.)
  27.       HRGN rgnClient = CreateRectRgnIndirect( &rcClient ); 
  28.       HRGN rgnVideo  = CreateRectRgnIndirect( &rcDest );  
  29.       CombineRgn( rgnClient, rgnClient, rgnVideo, RGN_DIFF );  
  30.  
  31.       // Paint on window.
  32.       HBRUSH hbr = GetSysColorBrush( COLOR_BTNFACE ); 
  33.       FillRgn( hdc, rgnClient, hbr ); 
  34.  
  35.       // Clean up.
  36.       DeleteObject( hbr ); 
  37.       DeleteObject( rgnClient ); 
  38.       DeleteObject( rgnVideo ); 
  39.  
  40.       // Request the VMR to paint the video and draw the point chosen by the user.
  41.       int i;
  42.       for( i = 0 ; i < azElPoints.size( ) ; i++ )
  43.       {
  44.          if( azElPoints[i].frameNumber == getCurrentFrame( ) )
  45.          {
  46.             mpOverlayLabel->move( azElPoints[i].xPos - 2, azElPoints[i].yPos - 2 );
  47.             mpOverlayLabel->show( );
  48.             break;
  49.          }
  50.       }
  51.       if( i == azElPoints.size( ) ) 
  52.       {
  53.          mpOverlayLabel->hide( );
  54.       }
  55.       HRESULT hr = pWindowlessControl->RepaintVideo( (HWND) mpVideoPlayer->winId( ), hdc );  
  56.    }  
  57. }
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You can see what I am doing is just showing/hiding the QLabel and then redrawing the video (ie. the QAxWidget) which in turns redraws the QLabel since it is a child of the QAxWidget. But when I click the screen, I want the dot (QPixmap/QLabel) to appear without causing the entire screen to flicker. Sometimes the screen flickers and sometimes it does not. And when it does flicker, sometimes the flicker lasts almost a half of a second - which is very noticeable. So any ideas on how to improve my function(s) to prevent this from flickering would be great! Thanks!