[FFmpeg-devel] [PATCH] lavc/vvc: Fix check whether QG is in first tile col

[Nuo Mi]

On Wed, Mar 20, 2024 at 3:48 AM Frank Plowman <post at frankplowman.com> wrote:

> The second part of this condition is intended to check whether the
> current quantisation group is in the first CTU column of the current
> tile.  The issue is that ctb_to_col_bd gives the x-ordinate of the first
> column of the current tile *in CTUs*, while xQg gives the x-ordinate of
> the quantisation group *in samples*.  Rectify this by shifting xQg by
> ctb_log2_size to get xQg in CTUs before comparing.
>
> Fixes FFVVC issues #201 and #203.
>
Thank you, Frank.
Pushed.

> ---
>  libavcodec/vvc/vvc_ctu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/vvc/vvc_ctu.c b/libavcodec/vvc/vvc_ctu.c
> index 519bd1ba76..8ba12c8d9f 100644
> --- a/libavcodec/vvc/vvc_ctu.c
> +++ b/libavcodec/vvc/vvc_ctu.c
> @@ -96,7 +96,7 @@ static int get_qp_y_pred(const VVCLocalContext *lc)
>      if (lc->na.cand_up) {
>          const int first_qg_in_ctu = !(xQg & ctb_size_mask) &&  !(yQg &
> ctb_size_mask);
>          const int qPy_up          = fc->tab.qp[LUMA][x_cb + (y_cb - 1) *
> min_cb_width];
> -        if (first_qg_in_ctu && pps->ctb_to_col_bd[xQg >> ctb_log2_size]
> == xQg)
> +        if (first_qg_in_ctu && pps->ctb_to_col_bd[xQg >> ctb_log2_size]
> == xQg >> ctb_log2_size)
>              return qPy_up;
>      }
>
> --
> 2.42.0
>
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