On Youtube, I hit the 'share' button, which gives me a short URL - copy and paste that into the text my post onits own line, and it shows up in the post.
Another thing I usually do is to select all on the text of a post and copy it before hitting the 'post' button, just in case something fails. That way, I can paste it back into the editor without retyping it all. It does not happen often, but just enough to make it worth doing.