[FFmpeg-devel] [PATCH 1/2] fftools/cmdutils: make the default swscale flags identical for simple and complex filter graph

[Nicolas George]

Linjie Fu (12021-08-01):
> Checked swscale, it uses bicubic by default.
> Scale filter sets the flags to bilinear if sws_scale_opt is not initialized
> by sws_dict.
> 
> We should use the same default flags for both simple and complex filter
> graphs, either from swscale, or from scale filter.
> If prefer to keep it identical with swscale, we may modify the flags in the
> scale filter.

Thanks. I also think that unless there is a good reason, we should rely
on a single default, from the lowest level. So:

- remove flags="bilinear" from vf_scale;

- remove setting defaults in ffmpeg.

Unless somebody can find a good reason for different defaults.

Michael, it is your commit, 8155bbc944c314fc202d31b0e4a3c77b8efc8dde,
that introduced it. Any comments?

Also, the current code in libswscale looks nonsensical:

        if (dstW < srcW && dstH < srcH)
            flags |= SWS_BICUBIC;
        else if (dstW > srcW && dstH > srcH)
            flags |= SWS_BICUBIC;
        else
            flags |= SWS_BICUBIC;

It was originally 6b3ff6f91a535d6383f41ca7bdf760165dcb6015 with some
logic, but it was cancelled by the merge commit
5710f55e490d0c3cf7348b3ca91c8c0fe4274be2.

"The default is left at bicubic until someone has compared the scalers
properly speed and quality wise."

But eight years later nobody did.

Regards,

-- 
  Nicolas George
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