I think you're talking about generating bitmaps of video, one frame at a time - which is a pretty different task from generating vector animation. If the LLM is approaching the task like an animator would (i.e. I want this shape to move here slowly for a long time, then grow rapidly for a short duration, then...) and expressing the result in some kind of keyframe animation format (Lottie, AE, Unity, etc.) then you aren't having to deal with the kinds of artifacts you described.