What designates the size of a replay file. Because sometimes you can create a replay 500 frames long that will be bigger then a replay file 1000 frames long. Is it just the amountn of joint clicks you have in that certain replay? That is my guess since it always seems like Swexx and largekilla always reach the maximum amount of space needed in a replay.

Seems logic. I think it is influenced by how many times you change status of joints. This is all the game needs to know to show you the replay.

Open replay in notepad. Look at what's included in it. For every meaningful frame (as in, when something changes), text for joint states and body position & movement is generated. So if you change something every frame, you will get a very bloated .rpl file. If you do single noobclap at the beginning and then extend pecs after 250 frames, you will only get the text generated for FRAME 0; and FRAME 250;.

this is also why hacked replays are so big, because most of them use the frame recorder script which records the position and movement in every single frame, so it is as if you moved something every frame