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Help With AE Motion Tracking

W

wheatgrinder

Hi all,
Im having a bugger of a time with my overly complex motion tracking project in AfterEffects CS3.

What I have is a scene, hand held, of an overlook of a city. Its a "home" video look where someone is watching the action and is whipping the camera from point of interest to point of interest...

There are whip pans, and almost 180 degrees of panning from start to finish of the shot. Also, the same view will come in, then go out, then come back in, which requires decent tracking across the entire shot.


So far I have been able to use the motion tracker and created several motion tracks, applied them to null objects, and parented the VFX and null tracks properly so that I have one MASTER null object that that seems to track ALMOST perfectly. The trouble is the "almost" inst good enough. :no:

Its seems I should be able to go in and hand tweak the keyframes that arent right, my method seems to be faulty as it has an unexpected side effect..

What Im doing is this;
  1. I find the place in the video where I want to "adjust the tracking"
  2. I open the null object into which I have applied the tracking data for that bit of the scene.
  3. I select all the keyframes for that null object.
  4. I adjust the position of null object using the slider controls (affecting multiple frames...)

which works fine. That part of the scene is now perfectly tracked and the overlay VFX look great...

Well, not so great because the REST OF THE TRACK is now off! All the parented null objects now seem to be OFF the exact same amount that I corrected for the "fixed" null object.

I'm guessing that the relationship between parents and children is two way. Or that step 4 in my process, selecting and adjusting multeiple keyframes has some other consequences that I dont understand.

The questions:
  • Is there another way to do this? Iv spent enough time that I could have hand tracked, frame by frame, the entire sequence, so I'm not above doing that! I just want a solid reference to hang my VFX's on.

  • Can I prevent the changes to child null object from being reflected in the parent?

I think I will try copying all the location key frames form the many null objects into ONE null object. And use that new null object as the master track. This I think will at least prevent the tweaks to one keyframe affecting another.



Thanks.
 
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Doing more web searching.. writing my problem out above is helping me to frame the questions for more accurate Google-ing..

I find on livedocs regarding multi selecting keyframes.. .. answering my question about step 4.

"You can also change the value of several layers at once in layer bar mode by parenting them."

Seems thats EXACTLY what is happening to me!
 
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M1chae1 said:
Have you run through the motion tracking tutorials on Video Copilot?

Maybe running through these few will help you solve your problem:

http://www.videocopilot.net/tutorials/the_healer/

http://www.videocopilot.net/tutorials/basic_sky_replacement/

http://www.videocopilot.net/tutorials/earthquake_with_32bpc/

Good luck.
Click to expand...

yeah, I LOVE those..
I feel that I understand tracking through the shot using multiple null data objects, its just the editing of the tracking data after the fact that is throwing me.

Seems I might have answered my own question already.. see above
 
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wheatgrinder said:
I think I will try copying all the location key frames form the many null objects into ONE null object. And use that new null object as the master track. This I think will at least prevent the tweaks to one keyframe affecting another.
Click to expand...
That's exactly what I did when I recently had a longer shot to track in AE. There's a plugin for AE called Mocha that helps with Motin Tracking and can do tracking even when points are not in the frame all the time. It's quite pricy though: http://www.imagineersystems.com/products/mocha/
 
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Tracking depends on recognizing pixel groupings between frames, if you've got a bunch of whip pans, there isn't any tracking solution that is going to just work... you're going to wind up having to do a good deal of keyframing by hand

But, the good news is that won't have to be totally accurate since you're going to have a great deal of motion blur from the whip pans.

So... Create a null layer for each of the points of interest, and from the first frame of the non-whip-panned part to the last frame of that part before another pan, track it in AE.. then apply those keyframes to the null.

After you've done each of them, go back and manually add keyframes before and after each that moves them far enough in the right direction of the whip pan. Once you've got that done, follow Andrew Kramers instructions on linking multiple nulls together, and you'll wind up with a bunch of nulls parented to each other that work together to give you basically a perfect track. Getting to that point is going to involve a good deal of manual effort though.

But, once done, you'll be able to move to the proper point in the timeline, add whatever you're going to comp in, and parent it to a null, turn motion blur on for it and the comp, and you're set.
 
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Will Vincent said:
Tracking depends on recognizing pixel groupings between frames, if you've got a bunch of whip pans, there isn't any tracking solution that is going to just work... you're going to wind up having to do a good deal of keyframing by hand

But, the good news is that won't have to be totally accurate since you're going to have a great deal of motion blur from the whip pans.

So... Create a null layer for each of the points of interest, and from the first frame of the non-whip-panned part to the last frame of that part before another pan, track it in AE.. then apply those keyframes to the null.

After you've done each of them, go back and manually add keyframes before and after each that moves them far enough in the right direction of the whip pan. Once you've got that done, follow Andrew Kramers instructions on linking multiple nulls together, and you'll wind up with a bunch of nulls parented to each other that work together to give you basically a perfect track. Getting to that point is going to involve a good deal of manual effort though.

But, once done, you'll be able to move to the proper point in the timeline, add whatever you're going to comp in, and parent it to a null, turn motion blur on for it and the comp, and you're set.
Click to expand...


Oh, I get it, I think! You let AE interpolate the whip pans, instead of what I did which is manually track them..
cool! VERY COOL

I dig your work flow, it focuses on getting the important parts right first. Doing it like this makes me think that my tracking of the whip pans was ending up a little "off" and thus the next tracking effort down the time line was a little more off, etc.. hence my need to go back and clean up, which is where I started having real problems...

My method seem to track OK, but my problem is (was) "making adjustments" to the child objects after the fact, and then having those changes find there way back into the parent, thereby screwing everything up. I believe (iv yet to prove it) the the root of my problem is that Iv been multi-selecting the keyframes, and adjusting them "relative" which seems to push up and down the child-parent hierarchy. (thats how I read the online doc anyway) but your flow should result in not NEEDING so much tweaking and that single frame adjustments may be all this is necessary..

Iv already spent several hours on this, whats another 3 or 4.

THANKS A BILLION!
 
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wheatgrinder said:
Oh, I get it, I think! You let AE interpolate the whip pans, instead of what I did which is manually track them..
Click to expand...
Not exactly.. You'll still have to manually add the keyframes, AE won't automatically do the inbetweens for you. But you will start and stop the tracker for each part that can be tracked by AE, and apply the tracked points to a null...

It's basically the same idea as what Andrew Kramer is doing in the Set Extensions tutorial, but since you can't rely on AE to track points during the whip pans, you'll have to manually add a few in there so that you can later parent the nulls to eachother as necessary.

What you'll end up with is a single null that moves properly throughout the entire shot that precomps or other layers can be parented to once they've been properly positioned at the right point on the timeline.
 
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Thanks for the clarification.

So, do I add the whip pan key frames to the existing null objects, or create new null objects?
Seems like it shouldn't matter.. new ones would be "cleaner" in my brain..

Thanks
 
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wheatgrinder said:
Thanks for the clarification.

So, do I add the whip pan key frames to the existing null objects, or create new null objects?
Seems like it shouldn't matter.. new ones would be "cleaner" in my brain..

Thanks
Click to expand...

It probably wouldn't matter. I think it would be cleaner to use the nulls that you're applying your tracking data to though, otherwise you'll end up with a lot of excess null layers that are only there to make the track work, and they junk up the comp a bit... Of course I think you are able to hide them if necessary, but anyway, the way it has to be done so that parenting things together works properly is to have a keyframe with the same relative position on the same from for the next null in the chain..

Follow the basic usage as explained in that set extension tutorial, and you should be able to extrapolate the method from there. You're a software engineer.. I've got faith you'll be able to work it out. ;)
 
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Ah Dang it! Im so close, but I end up with the same problem. Everything is looking close, but I as soon as I try and edit ANY of the keyframes in the child nulls everything shifts around in the parents, and since Im parenting about 20 nulls, it gets hairy quickly!

Thanks
 
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