How chapter seeking works?

[moi15moi]

I don't understand how chapter works.
So, to understand it, I created a sample: test_video_1127_ms.zip

The video contains 2 chapters.
The first chapter is named 0 ms and it's start time is 0 ms.
Same logic for the seconds chapter named 1127 ms.

I did those step to seek to the chapter named 1127 ms:

1. Launch the video.
2. Pause immediatly the video
3. Press PGUP to seek to the chapter named 1127 ms

It seek to the frame 27.
I'm surprised because the frame 27 time is 1126 ms.
I tought it would seek to the frame 28 which is 1168 ms since $$1127 ms \leq frame27PtsTime$$ is false.

Here is another sample where the seconds chapter is 1134 ms: test_video_1134_ms.zip
With this sample, it seek to the frame 28.

So, it seems that there is a buffer of 80 ms, so to know on which frame a chapter will be displayed, do I need to take the lowest $$frameTime$$ such that $$chapterTime < frameTime + 80$$ ?
Note that, in the formula, the $$frameTime$$ / $$chapterTime$$ are in milliseconds.