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I have some gopro videos I would like to convert from 4:3 to 16:9. Stretching uniformly or cropping is not a problem...but I would like to apply a non-linear stretch, with the lateral parts of the video more stretched than the center.

That's exaclty what is described in this video https://youtu.be/e74d2nHBhyI?t=59 The "Hor Dyn" control applies the distortion only horizontally and allows for getting better results in the center of the videos.

I tried the lens distortion k1-k2-k3 parameters in VFX but they distort also in the vertical direction. Same as using a lens distortion node.

So I'm stuck.

Any help is greatly appreciated. Many thanks!

Matt

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  • $\begingroup$ My first idea would be, if you can't do it in the Video Editor, maybe get the clip with "Images as Planes" import. If you then subdivide the plane you have to scale the UVs on the X axis with proportional editing, so that the outer parts get scaled more than the inner parts... $\endgroup$ Jul 2, 2021 at 8:06

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Elaborating on Gordon Brinkmann's suggestion, you can put your video as an image texture on a plane and then modify the coordinates e.g. using Vector Curves. Below, I've put two points on {0; 0}, {1; 1}, because those are the limits (beginning and end) of the UV coordinates, then a point on {0.5; 0.5}, as the middle isn't supposed to change, then two points between a middle and either of the limits: {0.25; 0.25}, {0.75; 0.75} and then adjust the Y value of those 2 last points to get stretching:

The animation is there to show changing Fac value is not equivalent to moving the points.

An alternative that's easier to adjust if you don't need the freedom of a curve, is to use to use the object coordinate -1..1, apply some mathematics (e.g. raise it to some power) and convert to the UV coordinate in the end:

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  • $\begingroup$ It could work...I'll play a bit with it. Thanks a lot! :) $\endgroup$
    – Matt Brown
    Jul 2, 2021 at 12:57
  • $\begingroup$ Yes, the second option was what I had in mind, only switched (the center stretched less than the lateral areas). $\endgroup$ Jul 2, 2021 at 13:28
  • $\begingroup$ Negative exponent will do that: i.imgur.com/CQQItVH.gif $\endgroup$ Jul 2, 2021 at 23:56
  • $\begingroup$ I can't manage to get the object coordinates to be -1, 1 and get a symmetric stretch. It should be something rather simple but I'm stuck... $\endgroup$
    – Matt Brown
    Jul 14, 2021 at 20:52
  • $\begingroup$ @MattBrown you can use a setup like this to easily check the coordinates: i.imgur.com/YxmPZSn.gif if your coordinates are wider/shorter, e.g. -0.7...0.7 then just divide it by that number to convert to -1...1 range. $\endgroup$ Jul 14, 2021 at 21:34

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