Yes, this is old. But idgaf. Why not use creative mode and F1 to get the mobs of the area to be there without taking notice of you? You could then set the render low and use that as background. Use creative to build a back wall and then spawn a ghast or two inside your little recording box, and they'll be forced to stay in the area. You could then use something like Fraps to record the entire section, seperate the game sound (turn music off first) from the clip. Take the clip and use a movie converter to turn it into a .gif, and then have the sound loop behind your looping animation so it seems as if you're in a continually moving environment.
Just an idea