Extracting an AAC stream out of a youtube video?

[Dwedit]

It's no secret that you add &fmt=18 to the end of a youtube URL, and you get a high H.264+AAC version of most videos there. It's a .mp4 file.
How do I use VLC media player to save the AAC stream to a new file, and have it playable in standard media players?

[Rémi Denis-Courmont]

I guess:
vlc [URL] --sout '#standard{mux=mp4,access=file,dst=[filename].m4a}' --no-sout-video