Many thanks to those involved in making this happen! AviSynth+ installed first time on pop!_os 19.10 (based on Ubuntu 19.10.)
In respect of ffmpeg, which repo is the "Sources" repo mentioned in the instructions? Here's the relevant portion of sources.list.
Code:
# deb cdrom:[Pop_OS 19.10 _Eoan Ermine_ - Release amd64 (20191019)]/ eoan main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ eoan main restricted universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ eoan-security main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ eoan-security main restricted universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ eoan-updates main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ eoan-updates main restricted universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ eoan-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ eoan-backports main restricted universe multiverse
deb http://us.archive.ubuntu.com/ubuntu/ eoan main restricted universe multiverse
deb http://apt.pop-os.org/proprietary eoan main
# deb-src http://apt.pop-os.org/proprietary eoan main
I know how to uncomment, but I'm not sure which one is meant. Perhaps it's enabled by default.