All language subtitles for 1. Using the Read Node

Hi there.

I'm Conrad, and welcome to my course on Retiming Footage in Nuke.

In this course we will cover all of the retiming options available to us from

the basics of adjusting frame ranges through to using optical flow technology to

make footage playback much slower than it was shot.

I'll also show you how to use expressions to link your

retimes to other nodes in your script.

In this lesson I'll explain to you the very basics of trimming down your

source material and setting up your Nuke project to match.

Nuke isn't great at browsing through large amounts of media,

so by the time we've got to the compositing stage of the project we will

want to know exactly which frames we will be working with.

This should be done in the edit suite,

and the edit should be locked before you start working on your visual effects.

We'll be working with this clip of a guy celebrating with champagne.

Let's assume we've already decided the part of the shot we

want starts at frame 220 and ends at 274.

This gives us 55 frames to work with.

So here we are in a new Nuke script.

You can see that by default Nuke creates a script

with a frame range of 1 to 100,

but when we load in our footage Nuke changes the frame

range to match the length of the clip, 0 to 360.

We want to change the frame range of the Nuke script to only

show the frames we've selected in the edit.

To change the frame range of the script we need to open the project settings.

You can do this from either the Edit menu or with your

cursor over the Node graph by hitting S.

We will set our first frame to 220 and our last frame to 274.

Now when we hit Play in the viewer we can see our selection.

In a simple world this would be it,

but imagine we have to add this clip to an existing project that

already had other clips and animated key frames.

If we were to adjust the frame range of that script we

would mess up all of our existing work.

Most video editing applications call the first frame of a clip frame 0,

but in Visual Effects we start at frame 1.

Actually, instead of frame 1 we usually start at 1001.

This gives us some wiggle room if the edit does change after we've started or

if we need pre-roll for any of our renders or simulations.

If we started at frame 1 and needed to add frames to the head of our

shot we would end up with negative frame numbers.

It's possible, but it would cause all kinds of complications,

so I'm going to set my start frame at 1001,

and my end frame at 1055, 55 frames in total.

Now if we go to our first frame and hit Play you'll

see that we have a frozen image.

This is because I've clicked when its frame range of 0

to 360 is well outside our new range, which starts at 1001.

Nuke is just holding the final frame of the clip as a freeze frame.

If we change this frame range dropdown from Global to Input it changes the

timeline to match whatever is connected to the viewer.

It doesn't change the project frame range that we just set.

This is useful to preview elements,

but to save confusion it's best to keep it set to Global while you're working.

So let's look at the different ways you can slip the timing of this clip,

so that it lines up with your project.

The first way is to use the controls inside the Read node.

Here you can select the range of the source that you want Nuke to read in.

I'm going to set the first frame to 220, and the last frame to 274.

Nuke will now ignore all of the frames outside of this range,

and treat frame 220 as the first frame of the clip.

This still hasn't slipped the frames in time,

but we can do that by selecting start at from this

dropdown and entering 1001 in this box.

This simply tells Nuke where in the timeline it

should start playing the footage.

In this case,

it is now going to start playing frame 220 of the

clip on frame 1001 of the timeline.

This is a very logical process,

but we're effectively trimming off the frames outside of our range.

Nuke will never read them in.

Usually this is okay,

but there are some operations that might benefit from having

extra frames outside of the working frame range.

We could leave the frame range as it was,

so we weren't losing any frames, but change the start frame to 781.

This shifts frame 0 of the clip to frame 781 of the Nuke timeline,

which means frame 220 lines up with 1001 of the project.

Let's look at the other options in the frame dropdown.

Offset slips the frames of the clip a given number of frames along the timeline.

An offset of one means that frame two of the footage now

lines up with frame one of the timeline.

A -1 offset would move frame 2 of the footage to frame 3 of the timeline.

So, in this case,

an offset of -781 would line up frame 220 of the clip

with frame 1001 on the timeline.

We could also use the expression option.

In this case, we would type in frame, -781.

This is telling Nuke not to look at the current frame,

but at a frame 781 frames back down the timeline.

In this case,

the expression option is overly complicated compared

to the offset or start at options,

but there are other expressions which makes this option more powerful.

We could, for example, use an expression to speed up the footage.

If we type frame*2 Nuke will take the frame number that we are viewing,

multiply it by 2, and then read that frame in from the source.

So frame one would become frame two, frame two would become frame four,

frame three would become frame six and so on.

Alternatively, we could slow down footage by a factor of 2 by using frame/2.

In this case, frame two becomes frame one,

frame four becomes frame two, and frame six becomes frame three.

You can see that the Read node isn't doing any frame interpolation.

It is simply rounding the result of the expression to the

nearest whole number and displaying that frame.

So if we wanted to have frame 220 line up with the first frame of our comp,

but then play it back at double speed, we could use frame-891 in brackets,

and then multiply the result of that by 2.

If we sped the clip up by a factor of 2 frame 220 would become frame 110.

Frame 1001 - 110 is 891,

so that is the offset we need to apply to the frame number after we have

sped it up to line 220 with our first frame of our comp.

So you can see that we can do quite a lot right inside the Read node,

but all these numbers can be a bit hard to visualize mentally.

This is why the foundry added the Dope Sheets in Nuke a few versions back.

It gives us a familiar timeline interface that helps us

with these time-based operations.

The Dope Sheet will display any Read nodes and certain

time nodes that are in your script.

We will also show any animated properties of any nodes

that are open in the properties bin.

With the Read node open you can see this gray bar that

represents the frames of the footage.

We can drag either end, like we would in an editing package,

to trim the frame range of the clip,

and we can slide the frames along the timeline to offset them.

You can see the properties change in the node as you

adjust them in the Dope Sheet,

and the resulting numbers are the same that we entered manually before.

So now that we have set up the project frame range,

and lined up the frames that we want to work with,

we are ready to start working on our shot.