Test video.<iframe width="560" height="315" src="https://www.youtube.com/embed/ck4t4R162aM" frameborder="0" allowfullscreen></iframe>
LOLYou guys are almost there!!!David, you apparently used the wrong link. Go to the youtube page and just below the video look for the Share. Click on that and then below that will appear Embed. Click on that and then the embed link will appear. Right click to copy it. Then....and Nick, this is what you left off, add the brackets and the html and brackets /html. Put your cursor between the brackets, right mouse click and paste the Embed URL. Or do like I do and type the bracket and html bracket, paste the URL then bracket / html and bracket.
LOLLike the other folks, no [ html] [ /html] at the beginning and end of the URL. I added it above and that is all I did, and it works.
OK - one more try and I give up.I have been doing exactly as you say, and putting html in  like these before and like these [/] after the embed string. Every time, whether I do it myself or I copy the string as you edited it in my posts above, when I try it, the Forum Software removes the html/brackets, leaving just the embed string, and the video does not embed. It's the Forum Software leaving out the brackets & html, not me.
HaaHaaMy apologies for not being clearer. I MEANT everyone was leaving off the [ html] [ /html] before and after the link and that's why it's not working. All you have to do is add those in front of and after the link. Sorry again...I think quicker than I type...or type quicker than I think....I think.