For reasons I can't even begin to comprehend at this stage in the day Youtube videos all have a url that begins https now...
You can post them in the pub but the amazingly clever pub software can't interpret them and present a preview of the video - it just shows the url...
You need to click the 'share' button and paste the url that gives in order to show the video preview...
For those of you that don't understand 'url', 'https', 'video', 'youtube' or 'pub' just post shite as normal and we will work it out....