Pasting a YouTube URL on its own paragraph (with a newline before and after) should work, as it’ll create a onebox in Discourse parlance.
Example in this thread (that’s also an onebox!):
Pasting a YouTube URL on its own paragraph (with a newline before and after) should work, as it’ll create a onebox in Discourse parlance.
Example in this thread (that’s also an onebox!):