Is there some way to "de-register" Quicktime for MP4 files? I have done this: 



(then click Open) about 4 times now. And yet the last time I clicked on an MP4 file it opened up in Quicktime. It's like OSX is ignoring what I told it to do. When I look at the file with Get Info it says it is an MPEG-4 movie. The default option under "Open With" is Quicktime. 

This is aggravating. How do I convince OSX that I really meant it when I checked "Always Open With"? 

High Sierra 10.13.4
Find one mp4 file. Right click, Get Info or  Cmd ⌘   I  

If not already set, select VLC in Open With, then click Change all... 



There's also the old faithful, RCDefaultApp which reports have said no longer works in High Sierra, but I just tested &amp; it appears to.