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Using a tracker to analyze motion in footage

From: Maya Rendering for After Effects Composites

Video: Using a tracker to analyze motion in footage

At this stage of Project 1, we have applied a tracker to the shot1 footage. Now if you open up the scene file, and you see that the tracker is missing, or at least it's grayed out, there is a way to get that back. We can just go Motion Source and change it from None, which sometimes it gets set to, to the name of footage that actually carries the tracker, in this case shot1, and it often comes back. Now if you still don't see it, it's possible the tracker is also set to None, in terms of Current Track. So just pick the tracker you are working with, like Tracker1 in this case, and then all these features come back.

Using a tracker to analyze motion in footage

At this stage of Project 1, we have applied a tracker to the shot1 footage. Now if you open up the scene file, and you see that the tracker is missing, or at least it's grayed out, there is a way to get that back. We can just go Motion Source and change it from None, which sometimes it gets set to, to the name of footage that actually carries the tracker, in this case shot1, and it often comes back. Now if you still don't see it, it's possible the tracker is also set to None, in terms of Current Track. So just pick the tracker you are working with, like Tracker1 in this case, and then all these features come back.

Also once this comes back, the Track Points should be visible on the layer view. Again, you have to do this in the layer view and not the Composition view. So if you are on the Composition view, switch over to layer view. In any case, we have the tracker, we have the TrackPoint positioned over the feature on that piece of tape which is the X. Now we are ready to analyze. So you can use the analyzation buttons down here at the bottom of the tracker. There is a Analyze forward it and also Analyze backward. This is based on what frame you're currently on. Now we set the Time slider on frame 10 because the X part was nice and clear at that frame.

So what we can do is choose to go one direction to the other. I am going to start by going forward. I will click the Analyze forward button. What happens is it's going to go through the footage one frame at a time. When it reaches the end in this case, it stops and what you're left with as a result is a motion path. If I zoom in closer, you can see the motion path is composed of both segments between keyframe boxes. These little hollow boxes are keyframes that are placed on the tracker's properties. The former path that represents where the X is going over time, or where that feature is going over time.

Now once the tracker stops, you can interactively play it back to see how well it's doing. You can just crab the time indicator and move it across, and we'd see how well that motion path is sticking to the center of the X. So, so far, the center of the X is pretty much lined up with those keyframe boxes. So we're doing pretty good at this stage. Now, we have only analyzed for frame 10 to the end, we start to do with Frame 0 through 9. So what I can do is go back to frame 10, then and use Analyze backward button, let's click that and see how that does.

Once it's done, it finished the motion path, and I can playback timeline and see how well it does. So here it's doing well, so go towards zero, pretty good, and now it some has an problems. See how it drifts off? So when I am on Frame 0, the center of that TrackPoint does not match some of the X. That's a problem. Why'd that happened? Well, there's lots of motion blur. Motion blur tends to confuse the motion tracker because pattern becomes too soft and blurry. Some really here the first two frames are a problem, after that it's doing okay.

So what do you do in that situation? Now this arises a lot because often the footage is so varied that you never get a perfect motion path at the start. There are several solutions. The easiest one in this case is to manually adjust the motion path to fix it, because we are only really dealing with two frames that are a problem in this case. What you can do is go to the problem frame like frame 0, zoom in and then interactively click-drag the box. Now I'm just going to drag it by its empty center to where you think it should be for that frame, say, about right here.

Once you let go, the motion path is Updated, plus a little keyframe box is updated. So Frame 0 is actually correct now. I can go to the next frame, frame 1 and again that one is off a little bit, so then I can click-drag the TrackPoint until it lines up. Again you are lying at the center so that little tiny center X needs to line up with the center of my big X on my tape. And you can adjust this as many times as you want to. All right. So frame 0 and 1 are now correct, and everything else looks pretty good. So we have been able to analyze the footage with the Analyze buttons, both forward and backwards, we've looked at how good that motion path wound up, and then we figured out a way to fix the first two frames which had drifted off. And the quick solution in that case is to manually adjust the TrackPoint position.

Show transcript

This video is part of

Image for Maya Rendering for After Effects Composites
Maya Rendering for After Effects Composites

34 video lessons · 5140 viewers

Lee Lanier
Author

 
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  1. 2m 0s
    1. Welcome
      47s
    2. Using the exercise files
      1m 13s
  2. 29m 49s
    1. Working with image sequences
      7m 24s
    2. Importing reference video as an image plane
      5m 13s
    3. Matching the 3D camera to the video footage
      4m 23s
    4. Lighting the model
      5m 35s
    5. Creating mattes and shadows in preparation for rendering
      7m 14s
  3. 15m 38s
    1. Using the Render Layer Editor
      4m 21s
    2. Splitting a scene into multiple render passes
      6m 6s
    3. Adding flexibility by assigning material and render overrides
      5m 11s
  4. 15m 2s
    1. Creating render passes using mental ray
      3m 50s
    2. Batch rendering render passes: Project one
      5m 24s
    3. Batch rendering render passes: Project two
      5m 48s
  5. 19m 4s
    1. Importing render passes into After Effects
      6m 25s
    2. Recombining render passes in a composition
      6m 31s
    3. Transforming multiple render passes as a single unit
      6m 8s
  6. 48m 7s
    1. Setting up a motion tracker
      5m 17s
    2. Using a tracker to analyze motion in footage
      3m 56s
    3. Adjusting tracker options for better results
      7m 2s
    4. Matching layer motion by applying tracker data
      6m 26s
    5. Refining a layer's transparency with rotoscoping
      6m 45s
    6. Improving layer movement with the Smoother tool
      5m 7s
    7. Improving the CG by adding blur and effects
      8m 7s
    8. Adding shadow to make the composite believable
      5m 27s
  7. 32m 36s
    1. Recombining render passes for project two
      5m 17s
    2. Removing unwanted elements with a garbage mask
      4m 57s
    3. Applying motion tracking data to a null layer
      6m 38s
    4. Adjusting shadows and matte edges
      8m 12s
    5. Using color correction to improve layer integration
      7m 32s
  8. 25m 46s
    1. Stabilizing shaky video with the Tracker
      8m 2s
    2. Tracking rectangular elements with the Perspective corner pin option
      5m 31s
    3. Adjusting corner pin points and paths
      6m 56s
    4. Applying corner pin data to multiple layers
      5m 17s
  9. 1m 16s
    1. Next steps
      1m 16s

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