Here is a good structure to compose image frame:

qt-x11-opensource-4.0.0-b2/tools/qvfb/qanimationwriter.cpp
It is as target only linux but i rewrite it to win32

http://fop-miniscribus.googlecode.co...emo_write_mng/

Compose image sequence

Qt Code: 
  1. void Gui_Main::setCaptureEnabled(bool enable)
  2. {
  3.       /* start stop QBasicTimer FrameTimeLine; */
  4. 	RRunning = enable;
  5.   if (enable && framerate > 32) {
  6.     FrameTimeLine.start(framerate,this);
  7.   }  else {
  8.     FrameTimeLine.stop();
  9.   }
  10. }
  11. QImage Gui_Main::CatScreen()
  12. {
  13.    QDesktopWidget *desk = qApp->desktop();
  14.    QPixmap desktopscreen = QPixmap::grabWindow(desk->screen()->winId());
  15. 	 QPixmap small =  desktopscreen.scaledToWidth(100);
  16. 	 devimg->paint( small );
  17. 	 scrollArea->setWidget(devimg);
  18. 	 delete &desktopscreen;
  19.    return small.toImage();
  20. }
  21.  
  22. void Gui_Main::StartRead()
  23. {
  24. 	  if (RRunning) {
  25. 			StopRead();
  26. 			return;
  27. 		}
  28. 	  QString filename = QFileDialog::getSaveFileName(this, "Save animation", "animation.mng", "*.mng");
  29. 	  if (filename.size() > 0) {
  30.     animation = new AnimationWriter(filename,"MNG");
  31.     animation->setFrameRate(framerate);
  32.     animation->appendFrame(CatScreen());
  33. 		setCaptureEnabled(true);
  34. 		}
  35. }
  36. void  Gui_Main::timerEvent(QTimerEvent *event)
  37. {
  38.     if (event->timerId() == FrameTimeLine.timerId()) {
  39.       timeline++;
  40.       qDebug() << "### timeline  " << timeline;
  41.       animation->appendFrame(CatScreen());
  42.     }
  43. }
  44. void Gui_Main::StopRead()
  45. {
  46. 	setCaptureEnabled(false);
  47. 	delete animation;
  48. 	animation = 0;
  49. }
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try it
1# svn co http://fop-miniscribus.googlecode.co...emo_write_mng/ movietest
2#
copy path from QTDIR /src/3rdparty/zlib & libpng to movietest dir

INCLUDEPATH += ui libpng zlib

and build it...

it write file .... but QMovie on read say:
MNG error 4097: Image is larger than defined maximum; chunk MHDR; subcode 0:0
MNG error 1028: Chunk-length is invalid; chunk MOVE; subcode 0:0

MHDR is a chunk format to learn and after you can register your image to a simple movie like gif animated ...

to look original search qanimationwriter.cpp on http://www.google.com/codesearch