I can't figure out a reason why Mastodon doesn't transcode remote GIF's, but for some reason it doesn't. Seems like a bug.
https://git.blob.cat/blobcatservices/blobcatstodon/src/branch/master/app/models/media_attachment.rb looks like it handles both local and remote media attachments, and I don't see it singling out local media for GIF transcoding only
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