Reflections in the trunk of the limousine

[Ivan De Mey]

A week ago there was an interesting post by Chris Bristow on Andrea Skolniks Facebook-group "JFK Assassination Books,Reviews and Discussion"

I found something of interest in Zapruders film. Watching reflections on the trunk of the limo you can see Jean Hills red coat and prior to that you can see those white concrete structures pass by and another witness' white shirt.
Right after Jean Hill and Mary Moorman you see what must be the brown cathedral. It is very distorted but regardless of what structure it is or whatever it is there is an anomaly. The other reflections, including the concrete structures move along the trunk and disappear within 5 frames or so. The brown building remains completely stationary(You can reference this by the edge of the building on the right side of the image) for almost 20 frames! In fact in the first few in creeps forward along the trunk until the image almost covers the length of the trunk. By frame 336 it is moving again and you see blue sky next to it.
Maybe it is two buildings and takes that long to move across, I can't make
sense of it.

This supports the idea the idea that the limo stopped during the head shot.
So is it a building or something else? How can it be stationary while the car should have traveled 30 feet in 2 seconds?

I tried to zoom in on the Zapruder-frames Chris Bristow is talking about, but the quality of the frames I have is just too low to see whatever he is seeing. A resolution of 260 KB per frame is just not good enough. Does anybody here see what Chris is talking about?