Changing Default File Types in Debian?

[Linux for blind general discussion]

Hi All: Last couple of days some of us were discussing mime types, as I want to 
play mp3s from Lynx. For some reason Debian defalts to alsaplayer rather than 
mpv, which I would rather use. Looks like xdg has some desktop tools, along with 
mime-open, but we couldn't really get these to work.
In Ubuntu vlc plays mp3s by default. In both cases I really wanna change to mpv. 
1 of the forum posts says I need to edit a "defaults.list" but locate doesn't 
find it. Can some1 please suggest a command to fix these. Thanks so much in 
advance
Chime