The issue is that clipping the interpolated temporal sample against
the spatially predicted sample causes artifacts to appear.

Discovered while writing the Vulkan version (where I omitted the
same check).

The clipping in the code is carried over from yadif. Removing the
same code in yadif does not make any difference to the output.
I think that the check was simply ill-adapted to the new prediction
code and does more harm.

I tested replacing the range clip with only an FFMAX, and only an
FFMIN, but in both cases, artifacts still appeared.

Test sample 1: https://files.lynne.ee/testsamples/mbaff_1080i60_idx.mkvTest sample 2: https://files.lynne.ee/testsamples/mbaff_bdmv_1080i60_8slice.mkv

Command line:
./ffmpeg_g -cpuflags 0 -i <INPUT> -vf bwdif=mode=send_field -c:v rawvideo -y <OUTPUT>.nut
Make sure to disable the assembly.

Comparisons:
https://files.lynne.ee/bwdif_01_before.png
https://files.lynne.ee/bwdif_01_after.png
Generated from sample 1 via:
ffmpeg -ss 00:00:00.184 -i <INPUT>.nut -vf crop=w=420:h=240:x=700:y=300,scale=iw*2:ih*2 -y <OUTPUT>.png

https://files.lynne.ee/bwdif_02_before.png
https://files.lynne.ee/bwdif_02_after.pngffmpeg -ss 00:00:00.417 -i <INPUT>.nut -vf crop=w=420:h=240:x=1100:y=200,scale=iw*2:ih*2 -y <OUTPUT>.png