macOS: brew install ffmpeg

https://github.com/matham/ffpyplayer/actions/workflows/pythonapp.yml is failing for thre months. * https://formulae.brew.sh/formula/ffmpeg > In file included from /Users/runner/work/ffpyplayer/ffpyplayer/ffpyplayer/clib/misc.c:2: /Users/runner/work/ffpyplayer/ffpyplayer/ffpyplayer/clib/misc.h:18:10: fatal error: 'libpostproc/postprocess.h' file not found #include "libpostproc/postprocess.h" ^~~~~~~~~~~~~~~~~~~~~~~~~~~ 1 warning and 1 error generated. error: command '/usr/bin/gcc' failed with exit code 1 error: subprocess-exited-with-error