After having to write two more programs (using Gamestudio), I finally got the video. The first program was to create all the screenshots. Due to file_for_screen requiring an extra number at the end, I had to bulk rename files. The second, since Virtual Dub doesn't allow for frames to be merged into each other as an effect to reduce the frame rate, was to create a script that read from 3 BMP images and merged them writing an output BMP to reduce the base 60 fps into 20. When played back, it's a bit tricky to tell if it's actually 20 fps or 60. Now all it needs is some (possible) audio, then, when that's done, a codec applied to it.