swfmovie->streammp3() streams the mp3 file mp3FileName. Not very robust in dealing with oddities (can skip over an initial ID3 tag, but that's about it). Like SWFShape->addJpegFill(), this isn't a stable function- we'll probably need to make a separate SWFSound object to contain sound types.
Note that the movie isn't smart enough to put enough frames in to contain the entire mp3 stream- you'll have to add (length of song * frames per second) frames to get the entire stream in.
Yes, now you can use ming to put that rock and roll devil worship music into your SWF files. Just don't tell the RIAA.