Tyrian, the infamous space shooter game for Windows, not only has input encoded demos but
lets you record your own demos using a hidden feature.
Command Line Parameters:
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Start Tyrian by typing FILE0001, and one of these parameters, and
RECORD -Records a demo of the current game and saves it as DEMOREC.x (where
"x" is a number in sequential order of the demo i.e. DEMOREC.1,
DEMOREC.2, etc...) in the current directory (How do you play them
back without renaming them to DEMO.x and overwriting the existing
demo files???!!!)
When I discovered this I tried recording a playthrough of Tyrian 2000's final level, Fruit, but to my younger self's sadness it desynced and I never made any attempts after that. I never investigated if the desync was due to playing with mouse or just the feature being buggy.