I have spent a lot of time this afternoon on this issue and I feel like this issue might not be fixable unless someone else has a brilliant idea.
The problem is in the virtual DOM with prepending (scrolling up). In this case, you are adding a bunch of elements (posts) to the beginning of an array. When the virtual DOM does its diff, it notices the element with the youtube <iframe> is not in the same place, so it removes and re-adds it later. This causes the youtube player to refresh the iframe, which causes it to play again.
It seems impossible to move an <iframe> in the DOM without reloading it.
Note that this bug doesn’t happen when scrolling down because appending posts doesn’t change the order. It also doesn’t matter if the user hasn’t started the video already, because lazyYT hasn’t inserted the iframe yet.
Sorry to resurrect this, but I’ve noticed this starts happening now even when scrolling down. Not sure if something changed this bug recently to the worse, or if it’s a different bug altogether. Confirmed with several people in our instance. This makes video sharing threads quite unbearable, when the earlier videos start suddenly playing.
I second this, happens with either scroll up or down and replays all previously played videos randomly (I imagine it has something to do with how Discourse processes previous content when loading new on a Topic, but I honestly don’t know).
I have mixed feelings about this, I don’t think people should have the expectation that a video from 600+ posts above will continue playing as you scroll down endlessly in a megatopic? The video isn’t visible, and hasn’t been visible for a while if you are scrolling down.
e.g. if you want to play audio for a long time while you browse around, on whatever site you’re visiting, open it in a new tab?
It shouldn’t, in my opinion. If the video is paused or finished it shouldn’t replay itself on its own just because you scrolled down. (Which is the described behaviour even though the title is misleading)
As a matter of fact, there is a an alternative for people that want “people to keep playing” as you go around, if they find the tab approach too much.