[Swftools-common] There's a transparent option in gpdf2swf, Where is it in pdf2swf?

[zzzhr]

Hello,I have been use swftools for weeks. Today, I got a problem:I can't
find transparent option in pdf2swf, but it must exist somewhere, since
gpdf2swf has this option (Edit -> Options -> No Viewer -> Make SWF
transparent). What should I do if I want make SWF files transparent in
pdf2swf?

Thanks.