[FFmpeg-devel] Controlling sws dithering.

[Michael Niedermayer]

On Wed, Jul 07, 2021 at 01:44:29PM +0200, Steinar Apalnes wrote:
> Hi,
> 
> I tried posting a similar question to the ffmpeg user list but got no
> response. So I'm trying my luck here now. The thing is I need to be able to
> control how the sws dither behaves.
> Using a build from master (26.06.2021) I would expect to see different
> frame hash on the these two commands:
> 
> ffmpeg -f lavfi -i mandelbrot -vf scale=sws_dither=none,format=rgb4_byte
> -vframes 1 -f framehash -
> ffmpeg -f lavfi -i mandelbrot -vf scale=sws_dither=ed,format=rgb4_byte
> -vframes 1 -f framehash -
> 
> But they are identical:
> b1c1ff5ea2221c0d0afaa86dec593491fd85fa2d5f5a377ff9c2e6c3ab5be5bb
> Also, the following variations creates the same results.
> 
> ffmpeg -f lavfi -i mandelbrot -sws_dither none -pix_fmt rgb4_byte -vframes
> 1 -f framehash -
> ffmpeg -f lavfi -i mandelbrot -sws_dither ed -pix_fmt rgb4_byte -vframes 1
> -f framehash -
> 
> Does anyone have a clue on what I might be doing wrong or is the sws dither
> control simply broken?

you found a bug, dither none was not supported for the codepath this used
i will post a patch fixing this in a moment

thx

[...]
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