So first things first, there is/was a fork of FFMPeg called LibAV. if you looking for docs on that, good luck!
libav (the actual code that makes ffmpeg tick) is a C library so we have to tinker with some low-level stuff
first off, install pkg-config brew install pkgconfig
should fix that for you.
ofcrouse you can install ffmpeg the same way if you did not do so already
now run: which ffmpeg
which should result to something like:
/usr/local/bin/ffmpeg
When we inspect this by running: ls -la /usr/local/bin/ffmpeg
we'll see this is a symlink.
on my machine the result is ../Cellar/ffmpeg/4.3.1-with-options_6/bin/ffmpeg
So the path we want is /usr/local/Cellar/ffmpeg/4.3.1-with-options_6/
when we go there we'll see lib/pkgconfig
which is where we want to point pkg-config to
I added the following to my zshrc:
export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/Cellar/ffmpeg/4.3.1-with-options_6/lib/pkgconfig
Now reload your shell (or source the file) run pkg-config --cflags libavutil
and it should return -I/usr/local/...