He's just rendering to a texture then displaying part of it on top of the scene again. That's why in the first video when he zooms in a lot the image is pixelated, it's not re-rendering the zoomed part at a new fov but just zooming into a rendered image. If you want your zoom function to be a pixelated mess and prevent you from aiming with any accuracy then go for it, but it looks like ass, unless you do it the proper way then you lose performance.
I'm not really sure I want a picture-in-picture zoom, anyway; if MW4 is anything to go by, it'll only serve to get in the way and make it harder to aim. MWLL's current zoom function is basically the same as MW2's, and works just fine.
I wonder if there are any performance gains using this now that you've shed some light on how this works Rajveer. The current zoom, though very intuitive, causes "hiccups" on majority of the maps which almost always causes assets to teleport (via sudden fps drops) when you're trying to zoom in on them.
Like ACE said, thanks to LODs, I would think that performance would be much better using a picture-in-picture zoom since it'll only cover a small area over trying to render all the textures in your field of view like the current default Crysis zoom does, if I understand it correctly. I would think that you could increase the texture resolution to prevent heavy pixelation when zoomed in though, but I could be wrong. And besides that, I'd be surprised if anyone would need to zoom in that much to take a shot
Terragent those are valid concerns, but I wouldn't worry too much about implementation. Pretty sure, should the devs even be considering something like this, that whatever they decide on would be significantly better than what was in that game.