Problem with youtube link IONIC 2

Ionic Framework ionic-v3
1

why can’t use it ? src="{{this.youtubevideo}}"

<div style="position:relative;height:200px;width:100%">
     <iframe width="560" height="315" src="{{this.youtubevideo}}" frameborder="0" allowfullscreen></iframe>
</div>
2

I don’t know.

What is happening that shouldn’t happen?
What is this.youtubevideo?