Words cannot convey how sketchy the MP4 codec scene was, pirating media in the Windows XP era. Every month you'd have to find some DivX CCCP K-Lite [cracked].7zip.exe and roll the fuckin' dice.
We were very proficient at reinstalling our operating systems.
VLC does use ffmpeg (or more specifically, libavcodec) for some of its codecs, but it uses a bunch of other libraries as well, including VLC specific ones.