A quick google shows me ActionScript 3.0 supports AAC.
Now just hope FirePlay was coded in ActionScript 3.0 instead of 2.0. 🙂
Sorry to say. It was coded in 2.0 to be able to compile as Flash6 to support some older platforms like the Wii.
On the other hand, playing single AAC-encoded files would not be possible anyway, since they have to be served by Flash Media Server, see this page:
And a quote in the article:
I am not in a position able to explain to you why we will not allow 3rd party streaming servers to stream H.264 video or AAC audio into the Flash Player. What I can tell you is that we do not allow this without proper licensing. Refer to Adobe’s friendly Flash Media Server sales staff for more information.
Too bad. It would be nice to be able to support AAC. Perhaps you can use the FireFly Java Client?