Deoldify Vapoursynth filter

[Dan64]

How does it compare to ddcolor?

  It depends on the model used, the Video model in "deoldify" has been calibrated to be flicker free in videos. Unfortunately in "ddcolor" all the models have some flickering.   
  The colors in "ddcolor" are more saturated while "deoldify" is more conservative and the color is desatured in order to avoid the flickering.
  The 2 models have different behavior and maybe the best result can be reached using them in combination (see Merge()).

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iirc render_factor slowed down deolidfy quite a bit, but helped with stabilizing the colors. (iirc. one needed to use 20+ to get usable results)
do you have any experience with this (it's quite a while since I last used deoldify)

Yes the render_factor controls the number of iteration for the convergence of the colors to be assigned to the image.
Higher values decrease the speed.
I forget to specify that a reasonable range of values for render_factor is between 10 and 44, being 21 a good default.
In term of speed render_factor affect the speed as input_size in "ddcolor".    
With render_factor=30, "deoldify" has about the same speed of "ddcolor" with  input_size =1024.