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Missing YouTube video thumbnails [fixed] (self.meta)

submitted 2 years ago* (last edited 1 year ago) by necropola to c/[email protected]

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Does anybody know why and when thumbnails for YouTube videos are shown or not? It appears to depend on the lemmy instance the posts are served from:

Without Thumbnails

With Thumbnails

Update: It's not only YT thumbnails which aren't shown. This is your post about the free 24 slot bag as shown on lemmy.wtf (without thumbnail), lemmy.world (without thumbnail) and feddit.de (with thumbnail):

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[–] necropola 3 points 2 years ago (1 children)

I also found this

https://github.com/LemmyNet/lemmy-ui/issues/20

There is an environment variable LEMMY_UI_DISABLE_CSP (default : false) to configure lemmy-ui. Do you set this on your instance or do you set a Content-Security-Policxy Header somewhere in your webserver/nginx config?

[–] [email protected] 1 points 2 years ago (1 children)

I just use the settings as it is shown in the installation guide for Docker: https://join-lemmy.org/docs/en/administration/install_docker.html

[–] necropola 3 points 2 years ago* (last edited 2 years ago) (1 children)

OK. Looks like the CSP headers are the same on working and not working instances.

What I found surprising is that chrome loads the thumbnail without accessing the actual YT URL (contrary to what I expected) from the "pictrs" server of the instance serving the post. Which means that the thumbnail gets only extracted once and is then stored along with the post.

[–] necropola 3 points 2 years ago* (last edited 2 years ago)

Brainstorming

Thumbnail extraction definitely happens in the backend.
- But when does it happen?
- Only when creating the post?
- Or also when federating a post to a new instance?
- PR which replaced iframely ➡ https://github.com/LemmyNet/lemmy/pull/1706
- Now backend uses fetch_site_metadata ➡ https://github.com/LemmyNet/lemmy/blob/main/crates/api_common/src/request.rs
- ... which evaluates the opengraph (og:*) meta tags from a linked HTML document whenever a post is created or updated
Thumbnails do neither work on lemmy.wtf nor lemmy.world but work on feddit.de
- Does feddit.de extract the missing thumbnail when creating/updating the post? ➡ Yes, I think so
- Or does it expect the thumbnail to be transmitted alongside the post? ➡ No, I don't think so
lemmy.world does not use cloudflare (I think) but they are also (like lemmy.wtf) using docker (I think)

Also Not Working on lemmy.world

https://lemmy.world/c/music

But does on feddit.de

https://feddit.de/c/[email protected]

It's not only YT thumbnails which aren't shown. This is your post about the free 24 slot bag as shown on lemmy.wtf (no thumbnail), lemmy.world (no thumbnail) and feddit.de (with thumbnail):