I had the same problem where any Anki card with audio spit out this error: Sound and video on cards will not function until mpv or mplayer is installed.
Your fixed worked! For those who are curious (on Mac):
- Ensure Anki is closed
- Open Finder
- From the menu bar, press
Go > Go to Folder...or pressCmd+Shift+G - Paste
/Applications/Anki.app/Contents/Resources/app_packages/anki_audio/ - Hit
Enter - Rename
libtolibs - Open Anki
