That's a pretty small photo, I can't really tell. Where was the video from? Is this one of the Virtual Railfan feeds? I am just guessing here, but it could be a ramp to unload MOW vehicles from the transporter flatcars. Here is a video link to the type of car I was thinking of: Kershaw produces the Scorpion flatcar where the ramp folds up into sections. Obviously that is not the car in your photo, but I think it is for a similar purpose. These are generally more common, and for MOW equipment moves over long distances, the train will usually have one of these at the end. I don't actually know of any cars that have one rigid ramp instead of the sectional one, but this is the concept that came to mind when I saw that photo. Here is another video:
I was thinking a pre-fab panel carrier too, but usually those have the frame tilted sideways on the car. I don't think transporting track like this would have much benefit over a regular flatcar. Having it angled the length of the car doesn't reduce the width of the piece the same that having it vertical does. Unless it is a part of a rail-renewal train. Some of those ballast cleaners and track layers have weird modified flatcars in them.
Thanks to all for your responses. Yes, this was from a railserve.com video feed of the Santa Fe junction in KC. It was by itself in the background and I do not see the car now, or it is far enough back I cannot make it out. There were no other cars around or near it to provide context. Thank you all again. cbg