Thank you both for help. I realized now, that I can't use Rotobrush if I open video in AE as "replace with AE composition" from Premiere Pro. But if I import video in AE then I can use it.
有时候抠图只能得到一个矩形紫色框，这是可能因为视频来自pr，而不是直接倒入到ae中，adobe的bug，我也是这个问题，纠结了很久，一直以为是自己操作问题，没想到被adobe阴了一下午。fxxk
