I tested swiffy out with http://leekspin.com/loituma.swf and it worked except for the looping music. It just plays the music through once. The animation loops just fine.
Gave up on swiffy a year ago. I couldn't get it to loop sounds either. The solution was to export the sound, copy and paste it (e.g. in Audiocity) the number of times I wanted it to loop, reimport it to the FLA and re-export to swiffy. In other words, swiffy didn't (looks like still doesn't) loop sounds. Also doesn't play streaming sounds and on mobiles there is no sound at all.