What???

你 know the red progress bar that's under a video when you're watching it that tells 你 how long the video is/how much you've watched? (pic related)
It's meant to resemble one of those.

The fact that the red line is there means you've watched the video to completion. A video 你 hadn't watched all the way would have a partially complete line, and a video 你 haven't watched wouldn't have a line at all.

I'm not sure, since I don't have a youtobe account. Since it is only found on the 视频 你 watched, it might 显示 that you've already watched them.

As far as the progress bar, that's what was happening to me. IDK about the rest.