[FFmpeg-devel] [PATCH] lavfi/bwdif: remove interpolated sample clipping

[Paul B Mahol]

On Sun, Jul 2, 2023 at 10:25 PM Lynne <dev at lynne.ee> wrote:

> Jul 2, 2023, 21:38 by onemda at gmail.com:
>
> > On Sun, Jul 2, 2023 at 9:13 PM Lynne <dev at lynne.ee> wrote:
> >
> >> Jul 2, 2023, 20:48 by onemda at gmail.com:
> >>
> >> > On Sun, Jul 2, 2023 at 6:57 PM Lynne <dev at lynne.ee> wrote:
> >> >
> >> >> Jul 2, 2023, 18:54 by dev at lynne.ee:
> >> >>
> >> >> > 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
> >> >> >
> >> >>
> >> >> Corrected links for the second sample:
> >> >>
> >> >> https://files.lynne.ee/bwdif_02_before.png
> >> >> https://files.lynne.ee/bwdif_02_after.png
> >> >> ffmpeg -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
> >> >>
> >> >> I'm sure I hit a newline. The artifacts are a lot more noticeable in
> the
> >> >> second sample.
> >> >>
> >> >
> >> > Single png images are not way to prove something.
> >> >
> >> > Please provide videos and not just single file that exhibit this
> issue.
> >> > (Keep showing same file over and over is not going to help show that
> it
> >> > helps)
> >> >
> >> > Also how PSNR/SSIM/VMAF changes before after not just in single sample
> >> but
> >> > in more samples.
> >> >
> >>
> >> I posted samples and instructions. Enough for a discussion.
> >> I'm not posting gigabytes of uncompressed samples.
> >> PSNR is irrelevant if there are visible artifacts.
> >>
> >
> > Nope, you havent.
> >
> > Some strange samples.
> > PSNR is relevant as also SSIM and VMAF.
> >
>
> Fair enough, on a 4k60 game recording, with lots of text and movement,
> ffmpeg -i game_4k60test.mkv -filter_complex "[0:0] split [t1] [t2] ; [t2]
> interlace [t2] ; [t2] bwdif=mode=send_field [t2] ; [t1] [t2] ssim [t3]"
> -map "[t3]" -f null -
>
> Before:
> 0.990397 (20.175775)
> After:
> 0.990417 (20.184970)
> Slightly higher, but not really significant.
>
> PSNR (average):
> 32.711758
> vs
> 32.704465
> Slightly lower, but not really significant.
>
>
Not very conclusive, I guess I need to test it myself on this sample
visually:

https://media.xiph.org/video/derf/y4m/west_wind_easy_1080p.y4m


>
> > Ignoring this does not help project, but just force tyrannic behavior.
> >
>
> Relax, I'm not going to make you write a stablediffusion filter source :)
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