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As long as we're talking about tracking in After Effects CS6, there's one more trick you should see. Here I have a composition with some handheld footage, shot with a DV camera, of a sign in France during a solar eclipse. Difficult-to-track shot actually. And here's the new sign we'd like lay on top of the old sign. mocha AE from Imagineer Systems, which comes bundled with After Effects, gets a really go track on this otherwise difficult shot. For better or worse, mocha used to be a stand-alone program that you had to it launch on its own, process there, then come back in After Effects.
Well, that process is a little more streamlined now. Just for fun, I'm going to go ahead and trim this shot to go from here to here, just so I have some trimmed in and out points. I'm going to right-click on this, reveal the layer source in the project, and see that this indeed interlaced footage separating fields, lower field first, 0.909 pixel aspect ratio. Great! Back in the composition, I'll make sure my footage to track is selected and I'll go to Animation > Track in mocha AE.
No need to go fish out a separate program; you can launch mocha from inside After Effects. But that's not all. Once I start up mocha, you'll see that it's loaded my clip; it has indeed separated the fields, Lower field first; it has the correct pixel aspect ratio; and it has what initially seems to be the wrong frame range, the entire length of the clip. But actually, that's okay. We'll accept this, and inside mocha we'll see it's already trimmed in and out points that match the in and out points I'd set back in After Effects. Very nice! But that menu item by itself is a pretty simple trick.
So as long as we are here, let's talk a little bit about mocha, because its user interface did change as of After Effects CS5.5. There used to be a whole set of additional commands and buttons down on the right side here, but they wanted to open up more room in the user interface for widescreen footage. Therefore, they moved a lot of nice easy-to-read buttons here into a lot of small incomprehensible icons along the top of the display. Let's go through a real quick track to familiarize you with where some of these are now. I'll choose my X-Spline tool. I'll do a really quick outline around this sign, like so.
If I wanted to, I could go ahead and tighten up the edges. But the nice thing about mocha is I don't need to be too precise in defining this region's track. My real area of focus is to replace the sign, so I'm going to define a planar surface that we want to corner-pin and drag those corners so they're just beyond corners of my sign. I'm looking at the little display in the upper-left to confirm that I'm moving these to the right area, just beyond the corner. Particularly, since this footage is a little bit on the soft side, it does have separated fields. There's a lot of interpolation going on. There! We'll track forward to the end of my region.
It goes by pretty quickly, actually. Notice that it's tracking every other field, one field per frame. That's not too bad, because sometimes separated fields can jump up and down. Let's drag the Current Time Indicator through here, and it looks like we have a good track, but to be sure, let's turn on the planar grid. This grid now tracks along with our defined surface. It can be a little bit hard to see whether or not it's really following the sign unless we customize the grid.
You used to have separate X and Y grid dimensions over here. It's now hiding underneath this little menu item. We'll open up the Viewer preferences. Now we'll use the normal Imagineer rotating user interface to go ahead and set these numbers somewhere around there, so we can go ahead and follow a nice tight grid around the sign. I'll close that, drag through here. If I go beyond, obviously the grid no longer tracks. But inside this area it seemed to track pretty well. Great! Let's export that tracking data.
Now, this step is still the same. You still need to decide what sort of data you want. I do indeed want corner pin data. I do want corner pin with motion blur. This gives me positional keyframes in addition to the four corners of the corner pin. I'll copy to the clipboard. A good working practice is to save a text file on your disk so you can archive it for later, but I'm in a hurry. Aren't you always in a hurry? Copy to clipboard, Command+Tab back to After Effects. Make sure your Current Time Indicator is at the start of your trimmed clip.
That way the keyframes that you just copied from mocha will match this clip's duration. Select the sign to be pasted to and Command+V or Ctrl+V to paste this data. I'll type U to reveal the corner pin data, Position, Scale, and Rotation. Since mocha had no idea how big the sign was going to be, it seems to be offset initially. Not a problem. Type A for anchor point and scrub it back. You'll find that the correct anchor point parameters are roughly one half of what would be the square pixel dimensions of this comp.
This is a 720x480 DV comp, square pixel would be around 654x486, and you'll see that our correct solution is indeed very close to half the dimensions of a 654x486 composition. There's your sign, type B to begin my work area, type N to end my work area, RAM Preview, and there it is. A pretty fast and pretty good track. So that's another little convenience they've slipped into After Effects CS6.
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