ffmpeg vertical pan over an image (top to bottom scrolling effect) I have a UHD wide image (3840px) which is very tall (11568px). I'd like to make a video like this:

3840 x 2160 resolution, mp4 output file
starts and ends black
image takes up full width of the UHD frame
top of the image appears at the bottom of the video frame and &quot;scrolls up&quot; until the bottom of the image disappears past the top of the video frame

It would be ideal if each step of the scroll shifted the image up 48px. But if it goes up 1 pixel every step because that's easier to script I can live with that. I'm trying to emulate something like an ANSI scroller where each line would present itself one at a time over a 28.8kbps modem after logging into a BBS 
I have found some similar questions asked but haven't figured out what parameters to tweak for the particular effect I've described. Horizontal scroll question on reddit. Ken Burns Effect Slideshows with FFMPeg blog post.
Thanks in advance for any help/direction
Create a canvas of output size and use an animated overlay to simulate a scroll.
ffmpeg -f lavfi -i color=s=3840x2160 -i UHDimage -filter_complex &quot;[0][1]overlay=x=0:y=H-48*n&quot; -vframes 242 out.mp4
Output duration is clamped to 242 frames = (11568/48)+1.