I'm new to audio (and signal processing in general), and I've been learning about the AAC codec. I've read that it supports 1-48 synchronous channels in a single stream. My question is: what need is there for 48 channels in a single audio stream? I understand that if you have a 7.1 speaker setup you can send a separate channel to each speaker, but what is the need for 48 separate channels?
Since it will most likely not hurt to have the possibility for more streams, this might for one be just to future-proof the system. Nothing would be more stupid than to specify for 8 channels and suddenly 9.1-systems become the next big thing and your codec is not suitable.
Other than that I can imagine bigger scenarios with much more channels such as recording all the voices in an orchestra. But I honestly don't know whether or not AAC is of any importance there.