The MAME Action Replay Playback Random Witterings Page

Q: But Aren't These Games Random?

> I was just playing with playback and i just remembered
> that everything in the game is RANDOM as it wasn't doing
> it the way i did it.

> this IS a bit of a problem as the playback is completely
> useless.

It's pseudo random. That is - it's random, but based on some kind of seed. There's no way for computers to make up random numbers, or to make up anything, really.

Games usually generate their 'random' numbers based on something from the player. Like how long it takes the user to insert a coin and press the start button. A difference of a fraction of a second in pressing the start button can make an entirely different set of random numbers. If you playback the same inputs with the same setup then the same things should happen.

Now, the .hi and .cfg files affect what's in the game's memory, so we should ensure that we all have the same stuff in these files, otherwise we'll get different random number sequences, and therefore get monsters appearing in different places and at different times. The easiest way to make sure we all have the same .hi and .cfg files is to not have them. That's why I suggest deleting the .hi and .cfg files before playing or recording a replay file.

There are scripts on the play and record pages which move the .hi and .cfg files out of the way for the duration of the game and replace them afterwards.

Another thing which affects some games (well, zookeep is the only one I've noticed it with so far, but please let me know if you find any more) is whether or not sound is enabled in the emulation. The zookeep files on my page require the sound to be turned on, or they don't work very well.

Curiously, one of the zookeep replays that I've seen runs fine for the first 2 rounds and the first coconut stage, but messed up on stage 3 if you don't have the sound turned on. Another messes up on level 1. I don't claim to understand this!

If you have problems with games not playing back the same as when you recorded them, try using my scripts, and if that doesn't work, try turning the sound on (or off). I'd like to know what you discover about this - maybe there's something else that affects the random number generator that we don't know about yet, but I can't think what it might be.

For help on how to play back replay files, click here.

For help on how to record your own replay files, click here.

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