黑板粉笔讲解动画Chalkboard explainer animation

一支粉笔在黑板上边画边讲，线条实时生长、偶有涂改重画。适合知识科普、课程片头、产品原理讲解。

Chalk lines grow across a blackboard in real time, with the occasional smudge and redraw. Built for explainer intros and how-it-works clips.