Most SWF videos are VP6 video with MP3 audio in a FLV container.

The best conversion from VP6/MP3/FLV to ASP/MP3/AVI would be to transcode the video, copy the audio as-is and remux the streams into an AVI container.

You might try iWisoft swf to avi converter which i've used, works well.

Alternatively, you could try FFMPEG. For example, the following command should do the trick:

ffmpeg -i SomeVideo.swf -vcodec libxvid -vtag DX50 -qscale 4 -acodec copy SomeVideo.avi