how to divide a video into several one in Matlab?

When using vision.VideoFileReader to read a video, I can not give a initial time like VideoReader('file.mp4','CurrentTime',30). If I need to step(vision.VideoFileReader) to a specific frame (eg. the frame at time =3s of the video), can I directly step to that frame? Now I need to step n=FrameRat*t times to that Frame. Do you have a short way? Or how can I simply divide a video into several parts without lose any information. When I try to use VideoWriter to make a new video, some information lost.