Best resizer in Avisynth?

[Master Tape]

I want to be able to downscale some videos, mainly SD footage which was recorded from a HD channel (upscaled)

Is there any good script that simply downscales the resolution without adding anything else (such as sharpening, edge enhancement, ect)

[pandy]

IMHO Spline34 or Spline64 - personally prefer spline resizers over other (most other resizer is build on principle windowing Sinc or windowing function itself and ringing is unavoidable - you can simplify that they approach is objective bandwidth/frequency not vision).
http://avisynth.nl/index.php/Resize
https://en.wikipedia.org/wiki/Spline_interpolation

[Master Tape]

I've heard good things about Spline. I was using BiCubicResizer but just entering the resolution i wanted it in and nothing else, but then again i don't know what else these resizers add when processing.

I've also just found out you can downscale/upscale in FFmpeg aswell (which i use to encode the .avs file) Don't suppose anyone knows if you get any artefacts that way aswell?

[jagabo]

"Best" depends in part on your source and whether you are upscaling or downscaling. Sharper isn't always better.

When I'm looking for a sharpening resize I usually use Spline36Resize(). It gives sharp results with minimal oversharpening halos, aliasing and moire artifacts. But when I'm downscaling a very sharp source I usually use BilinearResize(). That gives a more natural look without creating or exacerbating oversharpening halos, and the least moire artifacts. When upscaling SD to HD I usually used nnedi3_rpow2(), sometimes preceded or followed with a mild aWarpSharp() and Sharpen(). That's best at retaining sharp edges without creating aliasing artifacts and oversharpening halos.

[pandy]

I've heard good things about Spline. I was using BiCubicResizer but just entering the resolution i wanted it in and nothing else, but then again i don't know what else these resizers add when processing.

I've also just found out you can downscale/upscale in FFmpeg aswell (which i use to encode the .avs file) Don't suppose anyone knows if you get any artefacts that way aswell?

I think that quality of resizers are comparable especially on open source as they frequently share same code with some small modifications. Ffmpeg may deliver marginally lower quality due a less predictable behaviour - there are some issues in signal path related to color space conversion and quantization range - Avisynth on other way is very reliable on this as everything is explicitly controlled by you - no magic in behind (ffmpeg may call rescale silently and well it is written especially those older parts by people that don't care too much about accuracy of conversion - this is my very personal opinion about ffmpeg - unless you not doing research and you are not videophile purist then ffmpeg should be fine but if you need bitexact perfection then probably Avisynth seem to be correct choice).