EDIT2: I'm not really sure why people are having trouble with AAC, for me everything works just as expected o.O

EDIT: Got it to work! (It didn't want to mux automatically before) 5-stars for now as I have not found any other issues with it! It works just like the old version from what I can tell.

Pro-tip: In the settings where it asks you for the 'ffmpeg' path, make sure to write out the whole path to the .exe (like "C:\Users\[REDACTED]\Downloads\ffmpeg\ffmpeg-20171115-ff8f40a-win64-static\bin\ffmpeg.exe"), and not just to the folder itself.

Also, about that: Maybe a small piece of text making this completely clear could be inserted somewhere in the settings menu? (Since it isn't very clear right now what is meant exactly.) :)