- [Instructor] Tracking is a fundamental
skill required of all compositors.
In this brief overview of tracking,
we'll see how to set up trackers on their targets
and how to use the tracking data
for both stabilizing a plate and a matchmove shot.
So, the first thing we have to
do is add our transform tracker.
So we'll select our target clip,
come over to the transform tab,
come down to the tracker node.
Click and it opens up in the property bin!
Now the first thing you do when
you're tracking is you study your shot.
So we come down here and click play,
and I like to ping pong or bounce
my shot while I am studying it.
You're formulating your tracking strategy.
Now this is a particularly easy shot.
I chose it, 'cause it's a great training example.
Your shots will be much more difficult, I promise you.
Stop this and we'll jump the Playhead to frame one.
Now there are two kinds of tracking.
Auto tracking for easy targets.
You just drop your tracker and let her rip
for the whole shot.
For harder targets that are bouncing around
or have motion blur, you have key frame tracking
where we're going to drop key frames
at various points in the shot to help guide the tracker.
Let's start with auto tracking 'cause it's nice and simple.
We come over to our property panel and we'll click add track
and a tracker pops up on the screen.
We'll click and drag it over to our target,
which I chose this little guy here,
'cause it's such a nice, easy target to lock onto.
Before you start your tracking,
you have to go visit the settings tab.
This is where you set the parameters for the tracking task
and for auto tracking, this twirl down here
has a couple of important things for you to look at.
Always set the warp type.
This means what kind of motion
is the tracking algorithm looking for in the plate?
In this case, we're looking for both
translate and rotation but not scale.
We're not zooming, camera's not moving in and out.
So warp type will be translate and rotate.
The second thing is the error value here.
The way the tracker works is the first frame
you drop down, in this case frame one,
it snapshots that and saves it as the reference frame.
Then it compares frame two, to the reference,
frame three to the reference, frame four to the reference
and so on collecting an error code every time.
The further away it gets from the reference frame,
the larger the error becomes.
Whenever it exceeds this error value,
it'll snapshot a new reference frame
and resume the tracking from that point.
This is all transparent to you.
Okay, let's do some tracking.
So we'll come back up here, go back to the tracker tab,
and we'll come up here to our tracker controls.
This means to stop tracking.
Yeah, (laughs) you do not use the Playhead controls here.
You move the tracker. (laughs)
It has its own set up here at the top.
Okay, so stop tracking, track forward one frame,
track all the way forward to the end of the clip,
track forward a frame range.
And these are the same commands for tracking backwards.
Yes, you can track forwards and backwards.
Alright, let's give it a track
by saying track forward for the entire shot, go.
And off it goes.
You can see the error code down here, very tiny.
This was like I said a very easy track.
We get our tracking X and Y data up here
and as we scrub through the timeline,
you can actually see the code values changing.
That's telling you exactly where it was each frame.
Now, we're going to track another point,
but make sure I put the Playhead on frame one first.
Now, good technique is to track one tracker at a time.
So I'm going to turn off track one so I don't re-track it.
And then I'm going to add my second tracker
by saying add track.
I'm going to track on this little building over here,
position it just so.
Now I have to set my keyframes.
I have set my skip frame value here for 20
so I can just hop 20 frames and add a new keyframe.
You see, and it shows up over here.
First key frame, second key frame.
You want to make sure that these line up very well.
Okay, let's keep going, jump forward 20 frames,
set a new keyframe there,
jump forward 20, a new keyframe.
By the way, in a real shot, you would
not necessarily go exactly every 20 frames.
You would roll through the shot, looking for a big movement
and then you would drop a keyframe there.
You might have keyframes close together in some parts
and father apart in others.
This is simply illustrating the
process of keyframe tracking.
And we'll get our last frame in here.
You want to make sure that your keyframes are very close.
This one, number one looks like 21.
One looks like 41, one looks like 61,
one looks like 81, and one looks like 100.
Okay, if any one of these was seriously off,
we would have to correct it.
Okay, I love my keyframes and I am ready to track.
The keyframe tracking command is right here.
So, I do not have to position my Playhead on frame one now
because keyframe tracker always jumps
to the first frame in the timeline,
so play and we be trackin'!
And we're done, okay!
As I click on the screen,
it removes all of the tracking overlays.
Okay, I've got two good tracks
so I'm going to enable both of them.
Now, what's this TRS?
You can have many trackers in a plate.
You might have three, you might have 17.
What these letters up here are for,
is to stipulate this tracker, track one
will contribute to calculations of translation,
or rotation or scale.
I only want translation and rotation.
So I'm going to enable this tracker for both.
Track two, translation and rotation as well.
You might have a situation where one of the trackers
you only want to use him for translation,
so you would turn off the rotation.
If you don't do this, then you will
create a problem at the other end.
We go to the transform tab.
The transform tab tells the system
how to use the tracking data that you've just collected.
Now, you'll recall, that I set the trackers
to be both translate and rotation calculations.
So here are my translate and rotation calculations
right there, along with my center point here.
If I went back here and said, do not
use these for rotation computations.
We come back here, no rotation.
Okay?
So you have to set these correctly.
The transform tab, has a couple of missions.
Number one, the transform up here,
stipulates what the tracker node
is going to do to the clip itself.
If I set this to stabilize,
it's actually going to stabilize the clip.
Also, my data has switched to stabilizing data
that is, it just reverses all the values.
Let's take a look.
I'm going to turn off all overlays,
set my Playhead to the beginning
and I'm on ping pong or bounce as Nuke calls it.
Now let's push in a little bit just to challenge ourselves
and let's see how we did at stabilizing it.
I put my cursor right here and we walk through this shot
and my goodness it looks nice and steady.
They key point to remember is that
when you set it to stabilize, it's going to perform
a stabilize operation on your clip.
If you set it to matchmove, the data suddenly
switches polarity to a matchmove,
but it's going to perform the matchmove on your clip.
That's really not what you want usually.
So we set it to none.
Transform set to none means one, do not move my clip.
Two, interpret all my tracking data to be matchmove data.
So by default, you're getting matchmove data here.
So with that in mind, let's matchmove something.
Let's take this medieval tower, oh let me put my overlays
back on so we can see what we're doing.
We'll take this matchmove tower here.
I'll add a transform node to it,
and then we'll add a merge node
and comp it over our clip.
Of course, right now,
the clip is going to wobble like a son of a gun (laughs)
and the medieval tower is going to
be rock steady, so no matchmove,
What I need to do, is link matchmove
tracker data to the transform node
so that it'll move the tower before the merge node.
Alright, so we're done with this merge node
let's get rid of him, let's float this transform
property panel here, to help make this easier to follow.
I'm going to line it up carefully.
Okay, so now were going to perform the link
between the tracker node and the transform node.
Critical point, you must always bring the center over,
any rotation or scale has a center of rotation
and a center of scale, if you do not
link this over you will be wrong.
Command or control, click,
drag and drop, there is the center linked.
Rotation, command or control, click, and drop
and translate, click and drop.
Okay.
I can close my transform tab, and now,
I can close everything, and now we'll play
and have and admiration moment.
And there we go, Weinrich medieval tower,
beautifully matchmoved to a background plate.
Tracking is a skill that takes practice,
because each shot provides different challenges
to both you and the tracker node.
And you will have to track a lot
of shots to become truly proficient.