A plug-in that would upload a video (which a user had attached to a Discourse posting) to my company’s YouTube channel

[RGJ (Richard - Communiteq)]

There’s this theme component which I think does exactly what you need,
although I understand it’s currently unmaintained

Video Upload to YouTube and Vimeo using Theme Component

This new theme component enables video uploads from the Discourse composer to YouTube and Vimeo. For those already familiar with the plugin I developed recently, the same is now available in this Theme Component which can be added to any theme. This makes for a much easier installation and works in exactly the same way as the plugin. Features All forum members can upload videos to Vimeo or YouTube (admins can choose to enable either or both). Admins can control the view and embed privacy of th…