Continuing the discussion from Problems with thumbnails from Soundcloud and YouTube oneboxes:
When oneboxes are created with an iframe, we have no image to pull as a thumbnail. It would be cool if Onebox could supply an image for us to use.
Pavilion’s topic-list-previews plugin had this workaround:
But this has quite a large performance cost, so I don’t think we want to do it in core.
I see a couple of clean options:
Onebox could supply a thumbnail url. We would need to teach Discourse to fetch this and download it locally
We could implement something like lazy-yt which works for all iframe oneboxes. This may also bring some performance benefit, since the iframe content would not be loaded until after click
There are no immediate plans to implement this, but creating a topic here to track the idea.