Tutorial Guide of Using Twixtor

Dec 12, 2011

Slow motion has become very popular nowadays in the era of HDSLR. A high-speed camera is far out of our reach in term of affordability but there is another option which you can just shoot with your HDSLR and make the slow motion effects in post production. This can be done by using Twixtor.

In this post, we are featuring tutorial of how to use Twixtor by Elliott. Elliot wanted to share his knowledge of Twixtor so that everyone could benefit from getting the best results out of this tutorial.

In the first part of the tutorial Elliott demonstrates the main principles of Twixtor which you can apply to any video, and how to tidy up any unwanted warping.

Before you start, for best results use a shutter speed that will match your final frame rate to avoid blurry slow motion. Also, use the highest frame rate setting on your camera possible e.g. 60p, 60i or if you are using a 5D Mark II use 30p; The more frames Twixtor gets to play with, the better!

In part 2, Elliott explains Twixtor Pro and how you can take advantage of open and closed masks to help calculate where the pixels should move frame to frame. Resulting in a far better interpolated image.

Happy learning!

Part one

Part 2

BTW, I want to share with you this from a perspective of Philip Bloom.

 

Let me quickly explain how Twixtor works: It takes your footage [generally your transcoded 50fps, or 60fps footage and "guesses/interpolates" your missing/in-between frames

I guess with every project the approach is somewhat different. When Twixtor becomes a part of my workflow I need to become increasingly more aware of the way I am shooting so that I have workable footage in post.

I wanted to shoot something different to all the other Twixtor stuff I've been seeing - which have all been shot outside. I wanted to try shooting super slomo using the Canon 7D and Twixtor in interiors.

Here are a few key things to consider when working with Twixtor:

Shooting Workflow:

1. Shoot at a fast shutter: anything 1/2000 - 1/4000s. [so your lighting needs to be good]

2. Shoot against a plain/solid colored background – sky/wall etc etc.

3. Shoot at the highest point of action. The law of nature is that what must goes up, must come down. Its the movement at the top of an arc/trajectory that works best for Twixtor because that’s when things generally move the slowest, more frames of the relevant action for Twixtor to work with.

4. When you shoot really close/tight, slow the action down manually ie – move slower and fake slow motion [all the tight sequences in 'Gravity' was done this way and then slowed down a little more with the tools]. Its easier to get good results with Twixtor when the action is shot from a distance, because of the fact that the action will happen across more frames – ie – Imagine moving your arms up and down – a distance 50 centimeters right in front of the camera – the camera will only catch SOME of that action as your arms pass by the front of the lens, for maybe 1-3 frames. However if you move away from the camera and shoot say 10-15 meters away from the lens, you would catch the ENTIRE action across say 7-10 frames – giving Twixtor more information to work with

5. Shoot at 50 or 60fps. When you shoot high-speed you give Twixtor more info to work with – it is a shame that you have to forgo resolution

6. Shoot as much as you can – try to get the action from different angles – reshoot stuff if wasn’t working, or if your settings weren’t correct. SHOOT MUCH!

Post Workflow:

1. Use Twixtor in After Effects – for some reason Twixtor works best in After Effects – for me at least. Probably because After Effects’ ability to manipulate time is so effective.

So here’s what I do in a typical scenario.

- Edit the entire piece in an NLE [Non-linear Editor - like Final Cut] and then I’d

leave sections in the timeline open, or maybe reference clips that I want to

work with eventually in After Effects using Twixtor – you can’t do too much in

FCP at this stage because we’re going to be playing with time-changes – which

can screw up things if you don’t work carefully]

- Move the whole piece over to After Effects via an XML script called Popcorn

Island FCPtoAE. You need to export an XML from FCP by going to File >

Export > XML [ for FORMAT click Apple XML Interchange Format, Version 5]

- Open AE and go to scripts – look for FCPtoAE and then pull up the exported

XML

- Now click on the clip you want to use Twixtor on:  from the MENU go to LAYER

> TIME > ENABLE TIME REMAPPING. This allows you to extend a clip our for

longer – because when you start slowing stuff down, the clip needs to become

longer, which you can now easily do by enabling time remapping – just pull out

the edges using the drag function on the clip

2. Check that your Twixtor settings match your footage ie – Make sure your frame rate is correct when you set up Twixtor’s settings. If its not correct then Twixtor will stutter across your footage

- I typically shoot and edit in 23.976fps because I like the film aesthetic.

- I generally find that manipulating the image to a slower speed – say anything

between 2-5% yields better results than trying to get something workable at

30%. I don’t know why that is, but I reckon it has something to do with the fact

that with many more frames created it uses those created frames to reference

from in order to create more ‘interpolated/guessed’ frames.

3. Consider using an aspect matte to hide warping. I often use an aspect ratio of 2.4:1 in my work as a lot of my warping happens at the edges of my shots, thus a matte will hide the really bad sections. One instance of this was a shot in the short of mine called [Fo'tis'ma], where my good friend Franzwa is taking off from a ledge [Its the tight - slightly angled down shot at 34s]. The warping on his hand was REALLY bad – especially because the shot was rather tight and he was coming down at such a pace. It was because of that shot not working at 16:9 that I decided to make the whole piece 2.4:1 [IMAGE 1 & 2]

4. Avoid warping by editing well. Many times Twixtor works for only a few frames – if that’s the case I’ll only use it for a few frames and will cut to the next image – to avoid things looking crappy [obviously this must be done tastefully]. Don’t hang on too long on a shot that was good to start with but warped into mush at the end – EDIT WELL.

I trust this helps some of you out.

Source: Philip Bloom