Hi Nags, there is also the possibility to use the HTML5 video tag: https://www.w3schools.com/html/html5_video.asp when you enable controls in the video tag, you will have the ability to go fullscreen.
I've seen it with youtube but also vimeo that there is the option allowfullscreen. But this is not a default HTML parameter for iframe.
Can you provide more information about the source of the video files?
Thanks for your responses. This is not You Tube Video, the source is BrightCove player.
I found a workaround on this. I am using CKEditor now and copied the Iframe html content to render the video file. Now it works perfectly.