I use iWisoft SWF to FLV Converter to convert swf to flv which can be uploading directly to youtube or other video share website. The converted flv has the best quality and it's simply to use.

inputs: swf, flv
outputs: flv, avi, wmv, mov, mpeg, mp4, ipod, iphone, zune, 3gp, mobile phone, mp3, wma, wav, ogg, animated gif, gif, jpg, png, bmp, etc.

Additional functions:
Add watermark,
Crop SWF Video,
Trim any segments and merge them into one,
Free download online swf from any web page,
Take snapshots quickly and easily.
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