[FFmpeg-devel] [PATCH v9 07/13] vvcdec: add inv transform 1d

[Nuo Mi]

On Tue, Jan 2, 2024 at 11:55 PM Lynne <dev at lynne.ee> wrote:

> Jan 2, 2024, 14:01 by nuomi2021 at gmail.com:
>
> > On Mon, Jan 1, 2024 at 10:50 PM Lynne <dev at lynne.ee> wrote:
> >
> >> Jan 1, 2024, 15:16 by nuomi2021 at gmail.com:
> >>
> >> > + */
> >> > +void ff_vvc_inv_dct2_4(int *coeffs, const ptrdiff_t stride, const
> >> size_t nz)
> >> > +{
> >> > +    const int a = 64, b = 83, c = 36;
> >> > +    const int x0 = coeffs[0 * stride], x1 = coeffs[1 * stride];
> >> > +    const int x2 = coeffs[2 * stride], x3 = coeffs[3 * stride];
> >> > +    const int E[2] = {
> >> > +        a * (x0 + G2(+x2)),
> >> > +        a * (x0 + G2(-x2)),
> >> > +    };
> >> > +    const int O[2] = {
> >> > +        b * x1 + G2(+c * x3),
> >> > +        c * x1 + G2(-b * x3),
> >> > +    };
> >> > +
> >> > +    coeffs[0 * stride] = E[0] + O[0];
> >> > +    coeffs[1 * stride] = E[1] + O[1];
> >> > +    coeffs[2 * stride] = E[1] - O[1];
> >> > +    coeffs[3 * stride] = E[0] - O[0];
> >> > +}
> >> >
> >>
> >> Is that how the transforms are specified (matrices)?
> >>
> > Yes, a, b, c are matrix coeffs.
> >
>
> Awful codec design carried over from HEVC.
> Whatever.
>
>
> >> Also, why are you not adding the transformed residual *directly* to the
> >> input.
> >> This is how all our other decoders do this, because it skips a copy.
> This
> >> isn't
> >> something you can quite optimize later on.
> >>
> > It is possible, but it's a bit more complicated than other codecs.
> > For chroma, we need to perform lmcs_scale_chroma before adding it to the
> > residual.
> > Let's track it with https://github.com/ffvvc/FFmpeg/issues/177, and fix
> it
> > later.
> >
>
> At the resolutions VVC is designed to deal with, a fully memory copy
> can add significant overhead, and this could be tricky to do later on.
> It would also block SIMD code from being added.
>
> I wouldn't mind templaing the transforms for luma and chroma,
> and integrating lmcs_scale_chroma directly in the transforms.
> Would that help?
>
Yes, we can do many things here:
1. Make dsp function accept 2D instead of 1D (already done by
https://github.com/ffvvc/FFmpeg/pull/164).
2. Template it and incorporate LMCS-related things in 2D.
3. Implement the ASM code.
I plan to combine 1, 2, and 3 into one patch set.

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