I walk through many forums. I tried to apply proposed fixes but doesn’t work.
I loaded a new FFMpeg files from the linked shared on Audacity. Unzipped it. I made some experiments with placing dynamic libraries in the different folders.
It doesn’t help
System don’t want to recognised file
Even when I placed it at /Applications/Audacity/libavformat.52.dylib and pointed to this file in Preferences.
I also repaired all rights on the system.
MacOS 10.12.6 MacOS Sierra