There are four options, sorted by complexity:

• Homebrew (or other package managers)
• Static builds
• Docker
• Compile yourself

To follow this you need to have a bit of knowledge using a terminal/shell under macOS.

1. Homebrew

Homebrew has a formula for stable FFmpeg releases. This will get you running pretty fast. First, install Homebrew.

Then install FFmpeg through the ffmpeg formula:

brew install ffmpeg

This will download a lot of dependencies such as x264, but after that you should be good to go.

To update ffmpeg later on, run:

brew update && brew upgrade ffmpeg

2. Static Builds

The FFmpeg project, on the download page, offers links to static builds for ffmpeg, which you can just download, extract, and use in a terminal.

Static builds cannot contain every possible encoder, mostly due to licensing issues. If you don't care about the specific bundled encoders, this is a nice and portable solution.

Once downloaded, extract the file, open up Terminal.app, and navigate to the directory where you unzipped the files, i.e. where you find a file called ffmpeg. Copy this file to /usr/local/bin:

cd ~/Downloads/
sudo mkdir -p /usr/local/bin/
sudo cp ./ffmpeg /usr/local/bin
sudo chmod ugo+x /usr/local/bin/ffmpeg

Now, if you use zsh (which is the default shell since macOS Catalina), add it to your $PATH:

open -e ~/.zshrc

Add this to the file at the end:

export PATH="/usr/local/bin:$PATH"

If you are using Bash, instead edit this file:

open -e ~/.bash_profile

Save it, and close the editor. Now restart your Terminal and which ffmpeg should return /usr/local/bin/ffmpeg.

3. Docker

If you have Docker installed you can run a Docker container that comes with ffmpeg preinstalled.

There are various ffmpeg Docker images out there, for instance linuxserver/ffmpeg (see other answer below).

To run this image to convert an input.mkv file into an output file, open a Terminal and run:

docker run --rm -it \
  -v $(pwd):/config \
  linuxserver/ffmpeg \
  -i /config/input.mkv \
  -c:v libx264 \
  -b:v 4M \
  -vf scale=1280:720 \
  -c:a copy \
  /config/output.mkv

Note that $(pwd) will be your current working directory, and the command expects that directory to contain the referenced input file input.mkv. The file will be mounted into the container (into the /config directory).

4. Compiling yourself

You can of course build FFmpeg tools yourself, following the OS X compilation guide. This guide will always be up to date, and by manually compiling you may be able to tweak a few parameters.

This takes some time and experience with the shell, so it's not recommended unless you need to produce a specific build of ffmpeg.

To uninstall whatever version of FFmpeg you installed we'd need to know how you've installed it in the first place.

Since Homebrew will install to /opt/homebrew (for Intel-based Macs: /usr/local/Cellar), and symlink to /usr/local/bin/ffmpeg, it probably won't cause any problems with other libraries. However, check the make install scripts of the versions you (supposedly) built yourself and see where they placed FFmpeg. Then just delete them from there — it won't interfere with Homebrew.

The segmentation fault you got could be due to improper linking between the x264 or libvpx libraries. Since Homebrew will take care of this, you shouldn't run into any issues. However, I have occasionally run into an error like this when upgrading Homebrew dependencies without having upgraded ffmpeg — in this case, just brew reinstall ffmpeg and you should be good to go.