[FFmpeg-devel] [PATCH] avfilter: add scale2ref_npp video filter

[Timo Rothenpieler]

On 13.09.2021 11:07, Roman Arzumanyan wrote:
> This patch adds scale2ref_npp video filter which is similar to scale2ref, but accelerated by NPP. CLI sample:
> 
> 
> ./ffmpeg \
> 
>    -hwaccel cuda -hwaccel_output_format cuda \
> 
>    -i ./bbb_sunflower_1080p_30fps_normal.mp4 \
> 
>    -i ./920px-Wilber-huge-alpha.png \
> 
>    -filter_complex "[0:v]scale_npp=format=yuv420p[v0];[1:v]hwupload_cuda[v1];[v1][v0]scale2ref_npp=w=oh*mdar:h=ih/4[foreg][backg];[backg][foreg]overlay_cuda=x=(main_w-overlay_w),scale_npp=w=1280:720[out]" \
> 
>    -map "[out]" -c:v h264_nvenc -y ./output_overlay.mp4
> 

Some nits first:
Please configure your editor to get rid of trailing white spaces.

The commit message of the actual patch does not follow the usual schema, 
even though the subject of the mail does.

Missing a libavfilter minor version bump.

Missing docs. Can just be a simple docstring header referring to 
software scale2ref and normal scale_npp for identical options.

configure bits are missing. Just a second line otherwise identical to 
the scale_npp_filter_deps one.


Then, why is there a bunch of swscale stuff in the filter, which is then 
never used?
I'd guess those are leftovers from software scale2ref?
For example the swscale.h include, and calls to sws_freeContext in 
nppscale_uninit, and likewise the variables they refer to, of type 
SwsContext. They don't seem to be used anywhere.

The interlaced variable also seems to be never actually used, outside of 
logging it once.


Generally, the filter logic looks sound to me, which isn't surprising, 
given it's the same logic software-scale2ref uses, just some missing 
cleanup.
Would also love to see the same done to scale_cuda.

On that subject: I do wonder if there is some better way to implement 
the pretty much identical logic in multiple filters. Duplicating all 
that code is rather ugly and creates quite some maintenance burden if it 
gets enhanced/fixed in one of the filters but not the others.
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