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

[Nuo Mi]

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.

> 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.

>
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