GNU social comes with two plugins that add important media functionality.
Not talking neither about ImageEncoder nor VideoEncoder this time, but rather about StoreRemoteMedia and Embed.
StoreRemoteMedia
fetches remote files when they are Linked in a note. I.e., when the major mimetype isn't text.
It usually fetches and attempts to generate a thumb, if there are no encoders, it drops.
Embed
attempts to generate a page preview from opengraph and oembed. I.e., acts when the major mimetype is text.
We've changed so much with GNU social v3 that, regarding SRM there was no possible port, just a full rewrite. The code of both plugins became much easier of understanding and compact, while promoting the same functionality with more stability.
gnusocial