[grishka]

This is 1970s tech, so of course there was no compression. It's basically a composite video signal etched into the medium. Every revolution of the disc is one full frame (or two fields). So when you look at it, the adjacent grooves represent the same lines of video in different frames.

Now imagine if you picked a Y coordinate and extracted the corresponding row of pixels from every frame of a video file, and stacked them vertically. If there was scrolling text, or if the camera moved vertically, you would see a meaningful image, the same way a scanner obtains a complete image by moving a single-row sensor across whatever you're scanning. This is the same effect, just arising from the way the video signal is laid out on the disc.