Use @Orphis's FindFFmpeg module from ppsspp:
2149d3db7f
From that commit:
> This new module should be able to handle both libraries in the regular
> paths and fallback to pkg-config.
> It is also able to find dynamic libraries, not just static libraries.
> It will generate imported targets with the name FFmpeg::<lib> that you
> can use in your scripts.
d951d2e4c4