Posting of Youtube videos....When browsing the videos on the Youtube website, the only part of the link that is required is as per the blue highlighted text in the following image...
What you see after the unique video number, in the example above the '&feature=youtu.be' is not required and may prevent the embedding software from working. Note that sometimes the extra stuff after the unique video number might be different to what i have stated here, but either way it's not needed.
Also, when posting your link here you don't need to enclose it within the URL BBcode. The embedding software does all that for you so all you need to is copy and paste the link, like this....
If you do that correctly, you should see your video like this one...