One of the downsides of SWFMill (probably the only one) is, that it doesn't compress pngs, so things can get big pretty soon. If you need to convert a bunch of images into swfs and need transparency but compression, you can use the following script to achieve that by automating flash.

  1. var version = '1.02';
  2. var allowedFiletypes = ['png', 'gif', 'jpg'];
  3. var separator = '/';
  4. var defaultImageQuality = 90;
  5.  
  6.  
  7. fl.outputPanel.clear();
  8. fl.trace('Welcome to the wonderful convert images to swfs script (version ' + version + ')');
  9.  
  10. // create new project
  11. fl.createDocument();
  12.  
  13. // shortcuts
  14. var doc = fl.getDocumentDOM();
  15. var library = doc.library;
  16.  
  17. // set to player 8
  18. doc.setPlayerVersion(8);
  19.  
  20. // select images to import
  21. var importFolder = fl.browseForFolderURL('Select the folder with images to convert');
  22. var importFolderContents = FLfile.listFolder(importFolder);
  23. var i;
  24.  
  25. // import files into library
  26. for (i = 0; i <importFolderContents.length; i++)
  27. {
  28.     var file = importFolderContents[i];
  29.     var fileURI = importFolder + separator + file;
  30.    
  31.     if (!isAllowedFiletype(file))
  32.     {
  33.         continue;
  34.     }
  35.    
  36.     fl.trace('Importing ' + filenameFromURI(fileURI) + ' ...');
  37.     doc.importFile(fileURI, true);
  38. }
  39.  
  40. // choose export folder
  41. var exportFolder = fl.browseForFolderURL('Select the folder to which you want to export the images to');
  42.  
  43. // choose image quality
  44. var imageQuality = prompt('Please choose image quality', '90');
  45. if (imageQuality == null)
  46. {
  47.     imageQuality = defaultImageQuality;
  48. }
  49. else
  50. {
  51.     imageQuality = parseInt(imageQuality);
  52.     imageQuality = Math.max(0, imageQuality);
  53.     imageQuality = Math.min(100, imageQuality);
  54. }
  55.  
  56. var items = library.items.concat();
  57. var mcsFolder = 'converted_movieclips';
  58. i = items.length;
  59.  
  60. // convert all images to movieclips and export them
  61. while (i--)
  62. {
  63.     var item = items[i];
  64.     if (item.itemType == 'bitmap')
  65.     {
  66.         // set image quality
  67.         item.quality = imageQuality;
  68.        
  69.         var imageName = item.name.split('.')[0];
  70.         var mcName = mcsFolder + '/' + imageName + '_mc';
  71.        
  72.         // create movieclip in library
  73.         library.addNewItem('movie clip', mcName);
  74.         // edit movieclip
  75.         library.editItem(mcName);
  76.         // attach image
  77.         doc.addItem({x:0.0, y:0.0}, item);
  78.        
  79.         // get reference on mc
  80.         var mc = library.items[library.findItemIndex(mcName)];
  81.         // get reference on attached image
  82.         var image = doc.getTimeline().layers[0].frames[0].elements[0];
  83.         // we need to reposition the image, otherwise it will be centered
  84.         image.x = 0;
  85.         image.y = 0;
  86.                
  87.         var exportPath = exportFolder + '/' + imageName + '.swf';
  88.         fl.trace('Exporting ' + filenameFromURI(exportPath) + ' ...');
  89.         mc.exportSWF(exportPath);
  90.     }
  91. }
  92.  
  93.  
  94.  
  95.  
  96.  
  97.  
  98.  
  99.  
  100. /*
  101. * Helper methods
  102. */
  103.  
  104. function isAllowedFiletype(file)
  105. {
  106.     var suffix = suffixForFile(file).toLowerCase();
  107.     var i = allowedFiletypes.length;
  108.     while (i--)
  109.     {
  110.         if (allowedFiletypes[i] == suffix)
  111.         {
  112.             return true;
  113.         }
  114.     }
  115.     return false;
  116. }
  117.  
  118. function filenameFromURI(uri)
  119. {
  120.     var parts = uri.split(separator);
  121.     return parts.pop();
  122. }
  123.  
  124. function suffixForFile(file)
  125. {
  126.     var parts = file.split('.');
  127.     return parts[parts.length - 1];
  128. }
Download this script

If you open this script via Commands > Run Command, a file dialog pops up, where you need to choose the image source folder. Every gif, png and jpg in that folder will be imported. After that a new file dialog pops up, to select the target folder for the exported swfs. Finally you can choose the image quality (0-100) in the third dialog. The images will be exported to the target folder as swfs and done.