When you embed videos, you only use the last part of the URL, not the whole link.
For example if this is your link
https://m.youtube.com/watch?v=bjzyHAob7kw
You want to use the stuff after the "watch?v=" for the stuff you put in the youtube tags, which leaves you with
bjzyHAob7kw
Hope that helps. There's a image floating around here somewhere for this that I'm too lazy to hunt down that explains it better.