@Sammo77
On your older Roku Ultra model, when you run into the issue of the AAC codec, have you tried turning the Volume Mode to "Off", or to another mode to get the file to play correctly?
Start playing the file, press the asterisk (*) button on remote, under Volume Mode, toggle to "Off" (and then you can toggle back to leveling or night if you want), and see if audio now plays.
I have to do the above on my 4660 whenever I run into that issue.
On my Ultra 4802 and 4850, I do not have to do the above, but whether it is worth upgrading to save that little workaround volume mode toggle is up to you. (or if toggling to another mode is not working for you, as some also reported).
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, 4802, 4850, Premiere+ 3921, Express 4k+ 3941, Streambar 9102