[BUG]cant decode AAC audio stream

I have a video clip whoes audio encoded in AAC format in 48000Hz,in XBMC it was encoded to 96000Hz, so it can't play. I used ver12882 and many recently svn version, it appeared same. I trace the source code, find that AAC stream was decoded by AACodec.dl. Thus ffmpeg lib can decode AAC, why not use ffmpeg to decode it directly?
BTW, is there some document descript how to compile ffmpeg by myself?(I mean the compile options)