Which spline resizer is ffmpeg using?

[codemaster]

I found that there are 3 spline resizers: spline16, spline36, and spline64.

I'm encoding with this command:

ffmpeg -i "infile.mkv" ^
-codec:v libx264 -preset slower -tune film ^
-x264-params level=4.1:crf=23:min-keyint=24:keyint=240:colormatrix=bt709 ^
-vf "crop=1920:816, scale=1280:544:flags=spline, setsar=1" ^
-an ^
"outfile.mp4"

The version of ffmpeg I'm using is 4.3.1.

Question 1: For the above command, which resizer was used by ffmpeg to scale the image? spline16, spline36, or spline64?

Question 2: How do I specify, in the ffmpeg parameters, that I want ffmpeg to use the spline36 resizer? Or how can I prevent the use of spline16, and ensure that only spline36 or spline64 will be used?

[jagabo]

I think you want to use zscale instead of scale.
http://ffmpeg.org/ffmpeg-filters.html#zscale-1