1. record a video of your action
2. extract each frame as an individual image (the opposite to what you would do for a time lapse)
3. extract a vertical single pixel wide line from each image (for example a line from the center)
4. stack those lines horizontally from left to right to form an actual "slit scan" image
Sounds easier than sitting through an entire slit-scan video!
And I know that this video is about a year old, but if you haven't seen it before it's new to you!
I lost my mind trying to read your instructions.