Original subtitles

During this class we've covered some of the most useful

nodes in the ReSharper menu in detail.

There are lots of other nodes in the retime category,

but you could go your whole career without using some of them.

In this video we're going to quickly go through these nodes and

point out some scenarios where they might be useful.

The first two nodes, add and remove 3:2 pulldown,

are used when you're dealing with footage that has a 3:2 pulldown.

This is a process that was used to fit film shot at 24 frames a

second into NTSC video with a frame rate of 29.

97 frames a second.

This would spread four frames of the original film

across five frames of the video.

This worked because NTSC video is interlaced,

meaning that each frame is split across two fields.

Each field contained half of the image.

The 3:2 pulldown would map some frames from the film to 2

fields and some of the frames to 3 fields.

A 3:2 pulldown has to be removed before you start working Nuke,

so that you have whole frames to work with.

If you are rendering your finished images back to the same source you'll

need to add the 3:2 pulldown process back to your sequence at the end of

your Nuke script before you write out the frames.

You only need to worry about 3:2 pulldown if your footage

originated on film at 24 frames a second,

and it was then transferred to video tape,

and the video tape was NTSC.

I've never had to deal with 3:2 pulldown in my entire career,

partly because I used to work in a country that had PAL video instead of NTSC,

but as HD standards can now deal with native 24 frames a second 3:2

pulldown will only become less and less common.

The only time I can imagine you needing to worry about this is

if you ever get archive footage to work with.

The next node is AppendClip.

This simply allows you to play one clip after another.

You connect the clip you want to play first into the one input,

and the clip you want to play second into the two input.

The node deals with all the different start frames for you and

rearranges everything for you to play in sequence.

You can even create a cross dissolve and define how many frames it should take.

You can connect multiple inputs to the same

AppendClip node to create a sequence.

The FrameBlend node averages together a defined number

of frames to create a blended image.

It can be used in combination with some of the simpler

Retime nodes to create a smoother result,

but it won't be as effective as the other methods we've

covered in this class for creating motion blur.

If you add it to a moving clip you can create a cool motion trail effect.

If you have a static camera you can blend the frames together to

either create a single frame with reduced noise or grain or maybe

remove moving objects in the image, like rain.

You can see that if we apply it to the shot of the man with the champagne,

and blend the first 42 frames together,

we get a much smoother version of the background without

all of the ugly compression artifacts.

This would be useful if you wanted to use a single frame of the

image to create a patch or a matte painting.

The FrameHold node is very simple and really useful.

It simply freezes a sequence on a certain frame.

It also works with animated geometry and cameras.

I use it all the time, especially when I'm doing paint work.

The FrameRange node adjusts the first and the last frame of your clip.

It only effects how Nuke treats the sequence rather

than actually discarding the frames.

If you have your viewer range set to input,

then the FrameRange node will change the range displayed in the viewer.

If you use it in conjunction with an AppendClip node it

will change the timing of your input.

The other frames are still available outside the range that you define.

The TemporalMedian is similar to the FrameBlend,

except it creates the median rather than the

average value of the blended frames,

and it only uses one frame before and one frame after the current frame.

You can also use the core slider to limit the effect,

and only blend pixels together if they are similar.

The main purpose of this node is to remove noise or grain from a sequence,

but there are other more sophisticated Denoise options in Nuke these days,

so you probably won't use this node very often.

The TimeBlur node can be used to create motion blur.

It does so by sampling subdivisions of time between frames.

If you plug this into raw footage it doesn't have any effect because

nothing is happening between the frames at subframe level,

but if you have an animated roto or an animated transform

you can see that it samples the animation many more times

to create a motion blur effect.

The division slider defines how many samples the node will make.

The more samples the smoother the result, but the slower the calculations.

The shutter setting and the shutter offset defines how the samples

are distributed around the current point in time.

The TimeBlur node calculates everything above it in

your script for every sample.

If your script is big or they're heavy nodes this can get really slow.

You can place a NoTimeBlur node above the section of

your script that needs motion blur,

and it will limit the region of your script that gets calculated multiple times.

The TimeBlur setup was created back before some of the nodes

in Nuke had built-in motion blur settings,

but now that all of the transform and paint and roto tools have motion blur

settings in you really don't need to use this anymore.

The TimeClip node combines a lot of the features available in other nodes.

You can change the frame range of a clip,

shift a clip in time, reverse the clip,

and use an expression to change the speed of a clip.

This node was designed with a Dope Sheet in mind,

so it's a good option if you enjoy using that view.

The final group of nodes in the retime menu are based on motion vectors.

These motion vectors are the same kind of vectors that Kronos and OFlow

generate when they're using optical flow retimes.

The VectorGenerator produces three different channels; motion,

forwards and backwards.

These channels represent how each pixel is moving

relative to the frame before and after it.

Generating these vectors separately from the Kronos or

OFlow nodes has several advantages.

Firstly, they are relatively slow to generate,

so you can prerender them, and read them back in,

and connect them to Retime node to speed up your work.

You can use motion vectors from one image to distort a different image.

This can create some cool effects.

In this example,

you can see that if we create motion vectors based

on the man spraying champagne,

and use it to drive the retime of the basketball clip you get a really odd,

but interesting result.

You can use vectors to drive other custom effects that need to

be driven by the movement of your image.

The SmartVector node writes out motion vectors in a particular

format to be used with the VectorWarp node.

These are new tools in Nuke X that use vectors to track images

onto the moving surfaces of other images.

We won't cover that in this lesson,

but the vectors that are generated by the SmartVector node are similar to

the motion vectors generated by the VectorGenerator,

but they're stored differently.

If you have SmartVectors rendered out you can use the

VectorToMotion node to convert the SmartVectors to vectors

that can be used in a Retime node.

So to summarize this module,

cleaning up retimes can take a lot of time and effort.

Make sure that you have the retime approved before

you start the cleanup process.

You can use rig-removal techniques like painting,

patching and projecting to clean up artifacts.

There are lots of Retime nodes that you might never use.

Vectors can be generated from one image and applied to another.

This brings us to the end of the Time Shifting and Retiming in Nuke course.

I hope you've enjoyed it,

and you can use what you've learned to help make your

work even more exciting and dramatic.

To summarize some of the main points of the course try to make

sure that you have the timing of your shot correct before you

start working on more complicated VFX work.

There are many different ways to achieve the same result.

Make sure you think about adding motion blur to any footage you speed up,

and slowing footage down is a complex task for Nuke,

which will often result in artifacts that may need to be cleaned up.