White bars on the playback line in Video player of browser

[deep_space]

Those are chapter markers. They are placed wherever a chapter is indicated by your file's chapter file.
If you look at the very beginning of your screenshot, you can see they turn blue by default when you go past a chapter (watched).

If you want to hide them, add this to your custom CSS:

Code:

.sliderMarker.unwatched,
.sliderMarker.watched {
  display: none;
}

Oh thanks :)