I’m sure this is elsewhere a long way down this thread, so here it is back on top.
There are tags for youtube: [ Youtube ] and [ /Youtube ] - without the spaces, of course. (I put them in so the site wouldn’t try to process them.)
The link to your video is on Youtube, below the video under the “share” tab. Make sure the “share with playlist” box is unchecked to get the short link. Click share and then copy and paste the link to your LSC post.
The link to the video between the tags MUST be a plain text string, not a link, or the site ignores the tags and just shows the link. See some examples in the testing forum.
One way is to paste you link then retype the whole thing between the youtube tags.
Another (works on IE10 on my laptop) is to paste the link between the tags and immediately backspace once - that seems to remove the code telling the site that this is a link.