Set new startTime and endTime on videojs

Question

My problem is that I'm trying to reposition the start time and end time on the seek bar. My use case is this: i'm watching the video with a progress bar that go from 0 to 300 sec (e.g.). When i arrive at 200 sec, i want to set start time at 200 sec so the marker go to new 0 (old 200) and the stream continues. I'm using the last version of videojs and my code is not necessary because is almost native.