Original subtitles

In the previous video I showed you how to set up a

non-linear retime with the TimeWarp node.

In this video we're going to use that node as a master node

to control other retimes in your script.

I will also show you how you can export this data in a way

that can be used in other applications.

It's common to end up with several Retime nodes in your

script that need the same retime data.

Perhaps you want to use several Kronos nodes,

each with different settings for better results in

different areas of the frame or perhaps you have two layers

that need the same retime applied,

but you get a better result if you retime each layer

separately before you merge them.

Let's connect a Kronos node to this clip, and set the method to Frame.

We want to connect the Frame property and the Kronos node to the Frame

variable in the TimeWarp node that we set up before.

We can do this by opening the TimeWarp node and,

while holding down the Command key, Ctrl if you aren't on a Mac,

dragging the graph icon next to the frame variable to

the frame variable in the Kronos node.

You will see a little green circle up here in the

bottom right corner of the Kronos node,

and if you press Alt or Option and E you can see a green line

from the TimeWarp node to the Kronos node.

This signifies that the Kronos node has an expression

linking it to the TimeWarp node.

If you copy and paste the Kronos node,

the new node will also be connected to the TimeWarp node.

You can connect as many other Retime nodes to the

TimeWarp like this as you like.

This way the TimeWarp node becomes the master retime control.

Any changes there will be applied to all the other Retime nodes in your script.

You can also apply this retime data to nodes other than Retime nodes.

In this example,

I had a Multiply node that I have animated to create a flash

every time the guy's foot hits the ground.

I did this animation before I knew the footage was going to be retimed,

and now that we have the retime I don't want to

have to reanimate the whole thing.

I could connect the multiply before the retime,

but the flashing might mess with the results of the optical flow,

so I want to apply the effect after the retime,

but now the flashes don't match the action.

I can use an expression to apply the retime from the

TimeWarp to the animation of the Multiply node.

If we open up the TimeWarp node and hover our cursor over

the input frame control the tool hint will show us that the

control is also called lookup.

The name that shows whenever you hover over a property is the name that

you need to use in expression to refer to that control.

If we open up the Kronos node and right-click on the frame control,

and choose Edit expression, we can see that the expression says,

parent.

TimeWarp3.

lookup.

This is telling Kronos to use the lookup value from the node

TimeWarp3 at the parent or top level of our script.

Because the Kronos node is also at the top level of the

script we could delete the parent part, and the expression will still work.

Parent is only relevant when we start working with gizmos and groups.

Let's copy the rest of the expression.

Now let's open the Multiply node and choose Edit

expression for the multiplier value here.

Because this property has already been animated the

expression will already have the word curve.

This means that the node is getting the multiply value from

the animation curve in the Curve Editor.

This value changes over time,

so the node will read the value of the curve on each frame,

but if we add a set of brackets after the word curve,

and paste in the expression from the Kronos node we will now

be telling the Multiply node to read the animation value from

a different point on the curve.

Rather than reading the value from the current frame,

it will now read the value from the frame specified by the retime.

Now when we play it back you can see that the flashes match the action again.

As compositors we're usually the first department in the

VFX pipeline to deal with the retime.

Once we have it set up, and have got it approved by the editorial department,

we will probably need to send the retime information to other departments.

We usually do this by exporting an ASCII text file that

can be read by other pieces of software.

To do this open up your TimeWarp node,

and then right-click on the input frame value,

and choose File, Export Ascii.

With the default settings Nuke will create a simple text file with the

value of the retime curve for every frame on a new line.

Now if we open the text file we can see the numbers.

If we create a new empty TimeWarp node and choose File,

Import Ascii, and select the file that we just created,

we can see that the new node now has the same values as

the node we exported the text file from.

We can now send this ASCII file to other departments.

So to summarize this module,

working with speed values is often the most logical approach

when we're setting up a nonlinear read time,

but using frame numbers is more compatible with other software.

Often,

the editorial department has already decided what the retime should look like,

and we can use expressions to link retime information between nodes.

In the next module I'm going to show you some techniques

for cleaning up the retime artifacts, including using a 3D projection setup,

and some more uses for expressions.