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This is a problem I've been trying to come up with a solution for for a couple of days now, but wasn't able to.

Basically, I have an image sequence of a spinning tornado, which does 1 full loop in 32 frames, and I want to slow it down by a factor of 4. My idea was- since I want to slow down to 1/4th speed, I could make it do only a 1/4th rotation, instead a full rotation, which could be made into a seamless loop by creating 4 parallel animations, and offsetting them by 1 frame and cross-fading between them. But this didn't really work.

I also tried to introduce "steps" into the animation, by making each of the 32 frames last for 4 frames each, making the whole loop 128 frames long, and again, making 4 copies and offsetting them by 1 frame and overlaying them on top of one another, but that didn't work either.

If anyone could help me with this I'd greatly appreciate it. You can download the blend file with the image sequence here.

enter image description here

Here's the result with Luis Quintana's method:

enter image description here

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  • $\begingroup$ in the Output panel > Frame Range, there's a Time Stretching value that can allow you to speed up or speed down your animation, but if you have some physics it may not slow it down $\endgroup$
    – moonboots
    Mar 15 at 10:55
  • $\begingroup$ But that would increase the amount of frames the loop would be made of. I want to keep it 32 frames. There are no physics involved, this is just a looping vdb that I rendered into an image sequence. $\endgroup$
    – Geri
    Mar 15 at 11:12
  • $\begingroup$ I don't trully understand your question. Why not just slow down your tornado spin by 4, and increase your frame number by 4 ? You can't still have a full rotation and the same number of frames, if you want to slow it down. $\endgroup$
    – Lutzi
    Mar 17 at 18:57
  • $\begingroup$ From my post, I was trying to make it so that instead of looping once every full rotation, it would loop once every 1/4th rotation. I want to keep it 32 frames total for optimization, because I want to put it in a game. $\endgroup$
    – Geri
    Mar 17 at 20:32

1 Answer 1

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I suppose that you want to make a 32 frame duration loop.

To make a sequence loop fade in the sequence and over it, fade out the same sequence but with an offset so that the first frame and the last frame of the loop are the same.

To use the tornado loop as example:

In the Video Sequence Editor

(Shift-A) Add the Image Sequence and

(Shift-A) Add an Effect Strip>Speed Control (Stretch and Interpolation On).

Drag the end of the sequence strip to stretch it to the desired length.

Duplicate it and offset (Drag) it so the first frame of the sequence is the same as the last one in the timeline (this is a must for a smooth fade).

Select an effect strip, shift-select the other and with the effect strips selected (NOT the sequences) add a Transition>Cross.

Stretching to half speed you have this: enter image description here

In the timeline the first and last frames show the same sequence image, while the top sequence fades out, the bottom one fades in.

If you decide to stretch to a slower speed, you may choose a different section of the sequence but make sure you see the same frame at the begining and the end of the timeline.

EDIT: This is the method explained in a simple way.

You may have noticed that being the same the first and the last images of the loop, it freezes a frame when the loop restarts.

A simple solution for a 32-frame loop is doing the above but in a 33 frame timeline and render only the first 32 frames (in animation is common practice to key the loops at frame 0 and render from frame 1).

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  • $\begingroup$ Awesome, thanks! That worked. So basically the key was the interpolation. That will do the work of fading between the frames on the stretched sequence. Then I can simply place the 2 sequences end to end with an overlap that has the length of the original sequence. $\endgroup$
    – Geri
    Mar 18 at 18:59
  • $\begingroup$ I had to modify the workflow just a bit, since this method will will not work for images with alpha channels, so I used the shader editor for the cross fading. $\endgroup$
    – Geri
    Mar 18 at 19:01

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