Chapter timings question

[Simon_Haddad]

When inserting chaptermarks at I-Frames/keyframes in a mkv video, without 100% perfectly-accurate timings, is it better to err before or after the I-Frame/keyframe?

[manono]

I know nothing about MKV chapters, but have created thousands for DVDs. I always want them at scene changes. You choose the frame before the scene change and it chooses the next I-Frame (the one after the scene change) to set the chapter point.