[FFmpeg-devel] [PATCH v2 10/16] avfilter/vf_scale: strip metadata when changing colorspace

[Niklas Haas]

On Sat, 07 Dec 2024 22:47:57 +0100 Niklas Haas <ffmpeg at haasn.xyz> wrote:
> On Fri, 06 Dec 2024 10:17:48 -0500 Leo Izen <leo.izen at gmail.com> wrote:
> >
> >
> > On 12/6/24 9:32 AM, Niklas Haas wrote:
> > > From: Niklas Haas <git at haasn.dev>
> > >
> > > This is no longer relevant after a change in color space.
> > > ---
> > >   libavfilter/vf_scale.c | 12 ++++++++++++
> > >   1 file changed, 12 insertions(+)
> > >
> > > diff --git a/libavfilter/vf_scale.c b/libavfilter/vf_scale.c
> > > index e33617468a..a56d452c6c 100644
> > > --- a/libavfilter/vf_scale.c
> > > +++ b/libavfilter/vf_scale.c
> > > @@ -868,6 +868,18 @@ scale:
> > >       if (scale->out_transfer != AVCOL_TRC_UNSPECIFIED)
> > >           out->color_trc = scale->out_transfer;
> > >
> > > +    if (in->color_primaries != out->color_primaries ||
> > > +        in->color_trc != out->color_trc)
> > > +    {
> > > +        av_frame_remove_side_data(out, AV_FRAME_DATA_MASTERING_DISPLAY_METADATA);
> > > +        av_frame_remove_side_data(out, AV_FRAME_DATA_DYNAMIC_HDR_PLUS);
> > > +        av_frame_remove_side_data(out, AV_FRAME_DATA_DYNAMIC_HDR_VIVID);
> > > +        av_frame_remove_side_data(out, AV_FRAME_DATA_CONTENT_LIGHT_LEVEL);
> > > +        av_frame_remove_side_data(out, AV_FRAME_DATA_ICC_PROFILE);
> > > +        av_frame_remove_side_data(out, AV_FRAME_DATA_DOVI_METADATA);
> > > +        av_frame_remove_side_data(out, AV_FRAME_DATA_DOVI_RPU_BUFFER);
> > > +    }
> > > +
> > >       av_reduce(&out->sample_aspect_ratio.num, &out->sample_aspect_ratio.den,
> > >                 (int64_t)in->sample_aspect_ratio.num * outlink->h * link->w,
> > >                 (int64_t)in->sample_aspect_ratio.den * outlink->w * link->h,
> >
> > I think Mastering Display Metadata may still be relevant after a change
> > in TRC but not primaries (e.g. after linearization), since it only
> > references the gamut of the mastering display.
>
> That is true; but I think I'd rather handle this as a separate patch
> that re-attaches a modified / inferred set of MDM reflecting the new state
> after tone/gamut mapping.

In particular, we also need a way for the user to specify what primaries and
HDR signal range they want on the output, and whether or not they want any
inverse tone mapping / gamut expansion.

I will add an API like this to vf_scale in a later series; for now I want the
basic functionality to be in place and working.

>
> We need to strip the original and attach a modified copy in either case, and
> the status quo after this patch seems no less wrong than not stripping this
> metadata. (Otherwise, the behavior you get is something very strange like
> HDR-in-SDR curves and other things that one should not get by default)
>
> >
> > - Leo Izen (Traneptora)
> >
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