Animated Panorama
Vanilla Minecraft can't animate panorama_overlay.png, the texture drawn on top of the title screen panorama. This mod makes it possible: resource packs can animate the overlay with a GIF, a vertical PNG strip, or separate PNG frames.
If a pack has no animation, or the mod isn't installed, the normal static overlay is used, so packs stay compatible either way.
How it works
Put your files in assets/minecraft/textures/gui/title/background/ inside your resource pack.
GIF
Add panorama_overlay.gif. Frame timing is taken from the GIF itself.
One PNG with frames stacked vertically
Use panorama_overlay.png with the frames placed top to bottom (all the same height), and add panorama_overlay_animation.json:
{ "frames": 20, "fps": 12 }
You can give frame_height (in pixels) instead of frames. Without either of them, the PNG is treated as a normal static overlay.
Separate frames
Add panorama_overlay_0.png, panorama_overlay_1.png, panorama_overlay_2.png and so on. Numbers must be consecutive, starting from 0.
Speed
Add panorama_overlay_animation.json with { "fps": 12 } to set the playback speed. The default is 10 fps for PNG frames, and GIFs use their own timing unless you set fps. Loop length in seconds = frames ÷ fps.
Priority
If a pack contains several variants, the mod picks GIF first, then separate frames, then the vertical strip.