You may also follow this step by step guide to batch convert .swf to .flv for YouTube sharing
This guide can not only convert SWF to FLV, but also supports
converting SWF to MP4, SWF to AVI, SWF to MOV, SWF to MKV, WMV, ASF,
WebM, MXF, DV, RM, MPEG, etc.
It even can extract audio from SWF container and then save the
extracted audio files into like convert SWF to MP3, WAV, AAC, M4A, AC3,
DTS, CAF, AIFF, and FLAC and so on famous audio formats.
In this case, you can enjoy SWF files on almost all kinds of popular
players and portable devices like iTunes, QuickTime, Windows Media
Player, iPhone, iPod, iPad, Android, Xbox, PlayStation, BlackBerry and
so on.
Well, as for me, i always use iWisoft SWF to FLV Converter to do that swf to flv conversion. When you use it, you can choose the output format as .flv, then the program will automatically convert swf to flv with h.264 encoder which will make your converted video definitely to be the Youtube recommend uploading format h.264. I recmonded you Unit Conversion through this you get more results about Unit Converter .