Just copy the link that's in the URL bar.
This happens because when you right click the video and click "Copy Video URL" it copies a URL that XenForo's bbcode parser doesn't understand. This is because it contains extra information that let's YouTube's servers that the link was copied from that specific right click option.
The link given in the right click context menu is:
Code:https://www.youtube.com/watch?feature=player_detailpage&v=B6wvWlqRTfs
Notice that is has the extra "feature=player_detailpage&" in the URL? That's just data saying where the person got the link from.
The version copied from the URL bar is:
Code:https://www.youtube.com/watch?v=B6wvWlqRTfs
Notice how this version doesn't have that extra data and is understood by XenForo's bbcode parser? Good, carry on as usual...
Just so you guys know, I have fixed this issue!
The supported URL's from youtube are as follows:
Code:
youtube.com/watch?v={$id}
youtube.com/v/{$id}
youtu.be/{$id}
youtube.com/*/u/*/{$id}
youtube.com/watch?feature=player_embedded&v={$id}
youtube.com/watch?feature=player_detailpage&v={$id}
Check out this announcement:
http://offtopicz.net/threads/spotify-bbcode-plus-youtube-fix.77513/