Problem: I have several movie rips with 5.1 audio which I reordered the channels thinking that I needed to for AAC to have the correct order. I was wrong. I want to know if I can somehow reorder the channels without having to rip → reencode again. I’m also posting this in a couple other forums since this isn’t specific to Audacity.
Audacity works with uncompressed audio only, so an AAC file would be decoded on import and re-encoded on export.
One of the specialist video forums (such as doom9) will probably be your best bet.
I can’t say for sure, but that might not be possible… 2-channels AAC uses something similar to MP3 Joint Stereo or [u]M/S encoding[/u] so separate left/right streams don’t exist in the compressed data. I assume something similar is done with multichannel AAC.