Use Web Video Downloader to download Flash SWF online:
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By default, SWF capture function is disabled. To enable it, please select View > Options from the main menu. In the Video Capture page, make sure Flash Movie (*.swf) is selected in the file type list, as demonstrated below.
After the Flash Movie (*.swf) is downloaded, you can right click the file and directly open it with Sothink SWF Decompiler, as demonstrated below.