preview

import btpfunc as btp
import vapoursynth as vs
core = vs.get_core()
path=r'Path/to/video.mkv' #Don't forget the r before the path
src=core.ffms2.Source(path)  #you can also use src=core.lsmas.LWLibavSource(path)
src=btp.FFInfo(src, text='A', frame_num=True, frame_type=True, frame_time=True,color='0000FFFF')#Will print whether the frame is I/P/B along with their absolute time.
src.set_output()

Preview the script by pressing F5, in the preview panel at the bottom(Almost at the bottom center) you will find an icon for loading chapters, load the XML file for chapters. Use ctrl+right(forward) and ctrl+left(backward) to hover through the chapters, to check whether they are in sync with I Frames.