if something is going wrong with transcoding, the first thing to do is reading the log
in this case you'll see a lot of vapoursynth errors there, meaning the video was converted w/o interpolation script active
errors are PROBABLY because the video size after lavfi doesn't fall into the size range provided for RIFE: min_shapes=[2560,1440],max_shapes=[3840,2176]
a workaround for this is enable "perf. boost" in the RIFE proifle
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there's another problem here, not sure what could be a workaround for this one...
RIFE/trt wants frame size divisible by 32, thus SVP crops 16 px from the bottom (2160 -> 2144 px)
and it do so even after your lavfi transformation, making (1920;896) -> (1920;880), which is NOT divisible by 32 again
if you somehow will make (1920;912) in the lavfi - it will work