Camera can't reach 30fps, just keep 15fps

Mac OSX Lion i7
Cam: Logitech Pro 9000 (800*450@30fps on FMLE)
Study: Cirrus P2P streaming
Build in Flash builder 4.5 with FP ver 11.4.0

tried resolution: 320240 & 640360
setMode 30fps
Quality from 0-100
it keeps(always) around 15 fps by cam.currentFPS

no H264 code

How to fix this problem?