question about extract frames

when i extract frames video v_Mzojo2EeWu8, segment 3, frame_id 8. I use code from https://github.com/facebookresearch/ActivityNet-Entities/issues/1#issuecomment-529065386. But i just get 8 pictures(frame_id 0-7).The frame labeled is the ninth picture. I guess the reason is that the time of segment3 is too short, so how do I get the picture of the ninth frame? thanks a lot