In modern mode script we can end with

gmt end show

and then the plot opens up in the default viewer.I learned today via @Esteban82 that ffmpeg is one of many ff tools; the full list is

ffmpeg ffprobe ffplay

So a proposal would be if main.sh ends with gmt end show then once movie assembles the mp4 movie it would call ffplay, or perhaps just "open" like we do for images? Open movie.mp4 works fine on macOS (opens QuickTime player) - how about Windows and Linux?