Playing with Twixtor


Slow motion frame interpolation

Dave Newson - December 18th 2011

For a range of projects I was interested in how well we could do slow motion.

I have access to a Canon D60 (thanks girlfriend!) which can do 60 frames-per-second; this 60 FPS footage can be slowed down to 40% speed and rendered out 24 FPS, giving that filmic look. This is often how actual movies do slow-motion, as film cameras tend to have options of 24 or 60 FPS.

Despite this, I wanted to know if we could go even slower via software interpolation, and found a plugin for After Effects called Twixtor. Twixtor has the ability a step further than After Effects standard frame interpolation, which often results in blurry inter-fading frames, or very warped footage.

There really was no plan for the footage I would test this out with, I simply took the camera down to our local park to see what I could find. I found a Magpie.

For a range of projects I was interested in how well we could do slow motion.

I have access to a Canon D60 (thanks girlfriend!) which can do 60 frames-per-second; this 60 FPS footage can be slowed down to 40% speed and rendered out 24 FPS, giving that filmic look. This is often how actual movies do slow-motion, as film cameras tend to have options of 24 or 60 FPS.

Despite this, I wanted to know if we could go even slower via software interpolation, and found a plugin for After Effects called Twixtor. Twixtor has the ability a step further than After Effects standard frame interpolation, which often results in blurry inter-fading frames, or very warped footage.

There really was no plan for the footage I would test this out with, I simply took the camera down to our local park to see what I could find. I found a Magpie.

After trying Twixtor, I came to the following conclusions:

  • Interpolating 4 whole frames (10% speed) is a big ask; the software can sometimes go bananas for no good reason (see the fence, as marked in the video), and you’ll see a lot of inter-frame fading-blur on fast moving objects. You can probably reduce this by filming so that the slow motion footage includes blur on fast moving objects, but this is a little counter to what slow motion is about.

  • Interpolating one frame (20% speed) isn’t so bad, and you can probably get away with it so long as you don’t have continuous high-speed motion in your shot.

  • Interpolating blurry footage can still confuse Twixtor, so already mid-paced source footage which is clean and clear is probably the best source to use.

As a result, I’m not sure I’d recommend Twixtor for serious project-critial use. If you can get your mits on a higher speed camera, such as the 120 FPS of a GoPro HD Hero2, or ideally the Phantom Flex (I wish), you’ll be in a much better state.

If you’re just arsing about in your back garden however, who cares?


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