TL;DR
A picture says more than a thousand words. A video has many pictures.What?
Add a command line option to record the graphics output into a video file. This could be used while playing normally or for automatic runs. An in-game option to "record" gameplay would also be cool.This should work with all the benchmark options like running a savegame for a given number of ticks, with and without graphics being actually displayed. For this also add options to select an entity (e.g. sit in train <ID>), surface, position and zoom for the graphics output. Ideally this could be specified as a sequence of splines so the map can move smoothly and the surface can be changed at specific times.
Last an option to show the map view (with layer x,y,z) instead of a zoomed in surface view.