Can someone help me make a movie using decals or GUI that doesn't cause low FPS?

I'm making a game where there will be a movie theater. I am completely lost on how I'm going to even begin on making the movies. I've looked up on how to make gifs and found this

while true do
script.Parent.Decal.TextureId = "(asset id)"
wait(0.1)
script.Parent.Decal.TextureId = "(2nd frame)"
wait(0.1)
end

Whenever I try to use this, it ends up lagging my game much more laggy than I would like it to be. Can someone help me by telling me how I can make a movie on roblox but keep a high fps? Also another thing that would be amazing is if I could import 2D movies from Blender into roblox. Thanks for your help.