EDIT:
I've added a "non-free package option" so if you want to have Citra & proper music you have to pull in the code, alter one single var from no to yes & compile it. Basically copy & paste. This will build ffmpeg with fdk-aac support and so Citra should work with those specific aac files too.
non-free package option:
https://github.com/5schatten/libreelec.tv/blob/libreelec-9.x-rr/distributions/libreelec/options#l191
AAC-LC patents should expire this year so this will not be a problem anymore
Lots of patents expiring in 2015 - how relevant is MP3 still? - Page 3