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Explore how to use the motion tracker and stabilizer built into After Effects and shows how to handle a variety of shots. Author Chris Meyer leads a quick tour of the third-party software mocha and demonstrates the workflow for The Foundry's KEYLIGHT, both bundled with After Effects. The course also covers tracking a greenscreen shot with a handheld camera and replacing its background.
The After Effects Apprentice videos on lynda.com were created by Trish and Chris Meyer and are designed to be used on their own and as a companion to their book After Effects Apprentice. We are honored to host these tutorials in the lynda.com Online Training Library®.
I'd like to give you some additional advice on using the Tracker built into After Effects. If you haven't already, go ahead and Close All to cleanup your display, and if you have access to the Exercise Files I am going to go into the Sources folder, select this Mountain Peaks footage, and drag it to the New Composition icon and use this as my guinea pig for showing you these different ideas. I'll double-click to open it up in its Layer panel. That's where tracking takes place, and I'll do Track Motion to go ahead and create a Track Point. Now, one of the first things I do with every shot is I scroll through it to find whether or not I want to start from the back or start from the front of the clip and track towards its end.
One of the ways I make this decision is based on the size of the object I want to track. For example, if I start at the end of this clip, decide I want to track that peak, let's go ahead and move my Track Point over here, and carefully resize my Feature Region to match the size of that peak at this point in time. I have a problem when it comes closer. That peak will have gone larger, because it is closer, and it may outgrow the size of my Feature Region.
So instead, I look at when the object is its largest, use that as my starting point. Let's go ahead and resize this a little bit now. There we go. Get some of that shrubbery as well. And use that as my starting point for the track. So this particular shot, I start when that peak is close to me and track it toward the end of the clip, Analyzing forward. You don't need to start your track at the very start or very end of the clip, you can also go to say the middle of the clip and do your track in two parts. For example, I may set this up over my Track Point here, go into my Options, make sure they're set up properly.
I am tracking RGB since the color difference is greater than the Luminance difference here. Always have Subpixel on. It's not changing enough to Adapt Feature On Every Frame, but I do tend to set this to either Stop Tracking when my Confidence goes too low, or tell After Effects to automatically Adapt Feature at that point if the Confidence gets too low. Let me use Stop Tracking for now. Click OK. Remember my start point, 210 in this case, Analyze forward, and you'll notice by the way that my track did indeed stop before reaching the end of the clip.
I will press U and I will see that my Confidence did indeed drop below 80%. Now, if I think that the Track Point is still accurate, I can go ahead and continue from this point in time After Effects will take a brand-new snapshot of my feature at this frame, not back where I started, and then continue forward. So let's go ahead and finish the track in that direction. Now that I have done that portion of the track, I'll back up my Current Time Indictor to the point where I started and then I'll Analyze in the other direction.
Again, my Confidence fell below 80 %, After Effects stopped the track. I can see whether or not this looks like it's still on track or not. If it's not, I might need to start over with a different Track Point. But if it's still on track, I'll go ahead and continue analyzing from this point on until I'm done. Now, what this constant starting and stopping is telling me is that I do have some trouble with my Track Point. After Effects is having trouble following it in an accurate fashion. So I am going to go back to where I had a very high Confidence, like 100% here, and redo my Track Point.
And this is where things get tricky. I don't want to move my Attach Point. If I do, there will be a discontinuous jump in my keyframes that will then get pasted onto another layer. So if I want to adjust my Track Points without moving the Attach Point, I need to do one of two things. I need to be careful that I am moving just a corner of my Feature or Search Region, which does not move the Track Point. Or if I need to pick up and move these boxes altogether, I need to hold Option+Shift on Mac or Alt+Shift on Windows, which will allow me to move my Region without moving the Attach Point.
So I am going to reset this to maybe this area, this mountain to track. My Attach Point stayed here, but now I am searching on a region down here. I Analyze from that point back in time, and After Effects is much happier with that track. The Feature Region that I was tracking has a discontinuous jump, but watch the Attach Point. It remains continuous. So as long as you're careful what you are doing and that you're not moving the Attach Point, you can indeed alter the Feature and Search Regions during the middle of a track.
Let me show you another example of this. I am going to delete this Tracker. I am going to search through this shot to look for another interesting part of it to maybe add another layer to. Now, this little snowy plateau here does indeed look interesting to me. Say, I want to put something like a sign, a flag, or a man standing on that plateau. To do that, I'll Track Motion, pick something with high contrast track, like maybe that peak there or this peak off to the side. This peak off to the side has a lot of interesting details, because I have brown, I have green, and I have white, I have lot of contrast to track here.
But I want to move my Attach Point over to here, because that's where I want my flag or my man to be standing. I Zoom in and I reposition the Attach Point to somewhere in the middle of that plateau. I look at my Options, RGB track is a good idea here, because I have contrast and color. And I will keep the Stop Tracking option, because I was very instructive last time around. It will also demonstrate a bug in After Effects. I'll click OK and I will Analyze backward. Watch what happens. My track stops, because I lose Confidence.
I say, well, it still looks good, continue the track, and something has gone wrong here. The track continued even though the feature it was tracking went off the screen. This is a bug I've observed in After Effects before. For some reason the Stop Tracking doesn't work when the feature actually disappears. Well, believe it or not. That's not a problem. I am going to go ahead and look for my last good frame here. See, right there is bad, because they're staying in the same place even when the feature has gone off-screen. I'll say around there is my last good frame.
I don't want to move the Attach Point, because I want to keep my flag pulled there. All I need to do is find another feature in this shot to keep tracking in this point in time until that plateau goes off the screen. To move my Track Points without moving the Attach Point, I hold Option+Shift on Mac or Alt+Shift on Windows to get the four-headed arrow at the bottom of my cursor, and pick up and move this track region until I find something else good. Now that's something interesting right there, I've got this little black area in the middle of this red and green. I can probably even do a Luminance track on that rather than RGB track.
My Attach Point is still back here, but now my Track Point is over here. I'll Analyze from that point forward. I've stopped the track manually, because my point that I was tracking has gone off-screen, but that doesn't really matter to me, because now my plateau has completely disappeared and life is okay. As I scroll through this, watch carefully what's going on with this Attach Point. These keyframes indicate the Feature Region, and there is this jump in it when I relocate it to a new feature to track, but my Attach Point does indeed keep the same position on that plateau that I wanted to and even go safely off-screen as I follow my brand-new Track Point.
And I would cut off my track somewhere around there, because now my layer is completely off-screen and I don't need to worry about those keyframes anymore. I will Zoom back out and reposition my frame. So I hope that reduces some of your apprehension using the Tracker. You just need to think a little bit more about what is your tracking, then go ahead and track forward, track backward, or spice together multiple tracks to get the continuous result that you want.
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