record player replays from just inputs?

For an arcade game, I want to have it so you can download replays from the high score table.

From what I've seen, replays normally just record player input button presses. This makes a nice small replay file.

But this is only possible if you're doing a fixed framerate, like 60 FPS. Otherwise if someone has a different framerate, the timing of the inputs will vary and the playback will desync, breaking the replay.

C3 forces delta time and vsync, so we can't do a fixed frame rate.

I thought maybe I could just record the game at 30 fps, taking full snapshots of every object position, recording the game like a video. Similar to the follow behavior, but for everything. But for a 25 minute game, this kind of data would be huge, many megabytes, and I'm not sure if that's a good option?

Does anyone have any general idea for how to do a replay system that's possible in C3? Preferably lightweight.

thanks

25 minutes is a long time to have a replay! Perhaps a video recording would do the job? Saving positions every frame possibly isn't actually that bad - many megabytes of JSON data is not that heavy for most systems and should compress well too. Otherwise perhaps the Follow behavior would help. It can do record and replay and you can choose a lower history rate - which defaults to 30 FPS - to limit the amount of data saved, and it uses interpolation to smooth movement through the saved entries. I don't think it will do everything, but it sounds like it does a lot of what you need.

If you ran your game logic at a fixed rate you could do that.

One way to do that is to accumulate dt and once it’s big enough do the logic for a frame. So say try to run at 30fps:

var t=0 
Every tick 
— add dt to t 
While  
t>=1/30 
— subtract 1/30 from t 
— do all game logic for a frame here