OpenToonz: How to install ffmpeg for mac osx el capitan when only static ffmpeg builds for macOS 64-bit are available at ffmpeg.org?
At least one user found another answer hard to follow. So did I. After a bit of a struggle, I got OpenToonz 1.4 working with ffmpeg on a Mac running macOS Catalina (10.15). I installed the &quot;static files.&quot; I did not build from source. Here is what I did:

download ffmpeg, ffprobe, ffplay and ffserver from the download page. The download links are displayed in large green buttons and there are several on the page.

Extract these compressed files to your system.

copy the executables to /Applications/OpenToonz/OpenToonz_stuff/plugins

control(right)-click &gt; open each of the executables you moved into the plugins folder. This is necessary due to macOS security. The programs will run in the terminal and then report an error. That is OK.

open System Preferences &gt; Security &amp; Privacy. Go to the Privacy tab. Enable OpenToonz under the Accessibility category.

start OpenToonz. Open Preferences &gt; Import/Export. Set the file path for ffmpeg: /Applications/OpenToonz/OpenToonz_stuff/plugins


Restart OpenToonz. It should be working now (at least it was for me).
It was not clear to me which of the 4 executables OpenToonz actually needs so I installed them all. It would be better to find out which ones are actually needed and install only those. Maybe at some time in the future I'll do that.