Ask HN: Why does browser media always fail part-way?

I have the habit of watching various web videos in small chunks spread across the day.

When I come back to a video I get always get an error about media, network and failing and I have to reload the page to make it work.

I find it rather weird that the browser can't simply say "give me chunk K of this public video".

Youtube appears to work around this issue by auto reloading the page, so there seems to be a fundamental problem about videos.

What is happenning? and Why does this limitation exist?