You need the fancy SWF Tools cause you're working on a kickass project and need to convert stuff. You're shit out of luck cause you're also on Mac and SWF Tools has binaries only for Windows and you need to build it from the source for other platforms. On Linux I expect it works just fine but on Mac ...
You can get the source code and spend your entire day, week or life to get it working or you can get Mac Ports and have it handled for you:
sudo port install swftools
If port command is unknown then run it with the complete path
sudo /opt/local/bin/port install swftools
Done, I guess. It's still fetching / configuring packages while I am posting this, I don't see myself doing what it's doing automagically in the next decade.
Happy swftooling !