I used a combination of this thread and some help from ChatGPT-4, and got it fixed using these commands:
# remove the savory1 PPA:
sudo rm /etc/apt/sources.list.d/savoury1-ubuntu-ffmpeg*
# not sure if these were necessary, but can't hurt
sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
# manually install the packages over the existing savory1 ones:
sudo apt-get install libavcodec58=7:4.4.2-0ubuntu0.22.04.1
sudo apt-get install libavdevice58=7:4.4.2-0ubuntu0.22.04.1
sudo apt-get install libavfilter7=7:4.4.2-0ubuntu0.22.04.1
sudo apt-get install libavformat58=7:4.4.2-0ubuntu0.22.04.1
sudo apt-get install libavutil56=7:4.4.2-0ubuntu0.22.04.1
sudo apt-get install libpostproc55=7:4.4.2-0ubuntu0.22.04.1
sudo apt-get install libswresample3=7:4.4.2-0ubuntu0.22.04.1
sudo apt-get install libswscale5=7:4.4.2-0ubuntu0.22.04.1
# install ffmpeg
sudo apt-get install ffmpeg
It's apparently because the savory1 guy decided to start charging people for his PPA, but I really have no idea.
UPDATE (24 Mar 2023): The PPAs at this Launchpad site are now moving to a subscriber only (those who have donated) system. Given how many people and businesses are using these PPAs that I've put thousands of hours of energy into creating, and given the tiny amount of donations from all those many people and businesses, it is now necessary for the sake of my survival to restrict access to the most popular software at these PPAs to supporters.