As Reanimathor mentioned, you can do this pretty easily with something like an animated mask. Basically just have the two passes with a mask on one of them, then animate the mask to reveal it. You can learn about animated masks here: http://www.digitaltutors.com/lesson/31634
Hey Julienrashti -
So I looked at the demo reel and what I saw didn't appear to be anything too complicated. Of course there were a lot of composites over several layers but the technique is the same whether it's a single image or multiple. This can be done on a single frame or with an animation. First you will have to render your beauty pass and of course, whatever pass you want to incorporate as the effect e.i.; AO, Wireframe, Spec etc. either a still frame or animated sequence. Then you will have to drop them into your video editing program. Import your first layer and then place your second layer with a delay meaning, start layer one at 00:00 time and then the other when you want to have the effect. At the start of the second layer, attach a "Video Transition" to the beginning. The one that they are using is called a "Page Peel". It is a very common video transition. If you are using Adobe Premiere you can find this under the effects menu via Video Transitions/Page Peel/Roll Away. You can adjust the length of the peel but you may have to stretch the time slider to zoom in enough to actually grab the end of the transition to manipulate it. This page peel doesn't have a white line but there are ways to add that effect by inserting a "Chroma Clip" and then animating it across the screen to chase the edge of the page peel. There are lots of free chroma clips on the internet but you may find yourself wanting to create your own stylized clip to attach to your work. You can do this as well in your 3D software. If you wanted to create a white line you could render an overhead view of a cylinder with a transparent background and import into Adobe Premiere and translate the still image across the screen with the page peel. Or, you could say get elaborate and render say some particle effects like billowing smoke or flames to chase the page peel just render with a transparent background. Or maybe some sprites to create sparks or who knows whatever! You can get very creative just don't overdo it! I've taken the liberty to create a very primitive page peel from Beauty to AO and a reverse page peel back to Beauty of a model of mine to demonstrate the technique. I didn't add a chroma clip I only added the peel. Good luck and message me if you need any help.
Last edited by HellBender; 10-26-2013 at 07:24 AM.
Just to add to what has already been added here, I know the question of how to transition between passes for a demo reel have been asked before so I wanted to put together a quick video on a technique to do that. You can see this sort of effect in our Transforming Robot Production Pipeline Trailer at about 00:46: https://vimeo.com/37619844
Here's the video to walk through those steps. Hope it helps!