ffmpeg upgrade fails due to nettle no longer compatible with highSierra
As other answers have noted, Homebrew no longer supports High Sierra.
While I suspect you will eventually want to switch to MacPorts, you could also download a static build of ffmpeg from https://evermeet.cx/ffmpeg/ and drop it in /usr/local/bin. These self-contained &quot;static&quot; binaries include all of the library code they need to run.