Re: [FFmpeg-devel] [PATCH v2] lavc/vvc: Fix NumEntryPoints derivation

[Nuo Mi <nuomi2021@gmail.com>]

On Thu, Mar 6, 2025 at 2:40 AM Frank Plowman <post@frankplowman.com> wrote:

> If pps_single_slice_per_subpic_flag is 1,
> slice_{width,height}_in_tiles are undefined and we must instead get the
> dimensions of the slice by referring to the corresponding subpicture.
>
> Signed-off-by: Frank Plowman <post@frankplowman.com>
> ---
> Changes since v1:
> * slice_height_in_tiles is also undefined if
>   pps->pps_single_slice_per_subpic_flag is 1,
>   so also derive that from the subpic info.
> ---
>  libavcodec/cbs_h266_syntax_template.c | 49 +++++++++++++++++++++++----
>  1 file changed, 43 insertions(+), 6 deletions(-)
>
> diff --git a/libavcodec/cbs_h266_syntax_template.c
> b/libavcodec/cbs_h266_syntax_template.c
> index 58211026bb..05634bc19c 100644
> --- a/libavcodec/cbs_h266_syntax_template.c
> +++ b/libavcodec/cbs_h266_syntax_template.c
> @@ -3440,13 +3440,50 @@ static int FUNC(slice_header)
> (CodedBitstreamContext *ctx, RWContext *rw,
>              for (i = 0; i < current->curr_subpic_idx; i++) {
>                  slice_idx += pps->num_slices_in_subpic[i];
>              }
> -            width_in_tiles =
> -                pps->pps_slice_width_in_tiles_minus1[slice_idx] + 1;
>
> -            if (entropy_sync)
> -                height = pps->slice_height_in_ctus[slice_idx];
> -            else
> -                height = pps->pps_slice_height_in_tiles_minus1[slice_idx]
> + 1;
> +            if (pps->pps_single_slice_per_subpic_flag) {
> +                const int width_in_ctus =
> sps->sps_subpic_width_minus1[slice_idx] + 1;
> +                const int subpic_l =
> sps->sps_subpic_ctu_top_left_x[slice_idx];
> +                const int subpic_r = subpic_l + width_in_ctus;
> +
> +                int ctb_x = 0, tile_x = 0;
> +                for (; ctb_x < subpic_l && tile_x <
> pps->num_tile_columns; tile_x++)
> +                    ctb_x += pps->col_width_val[tile_x];
> +
> +                width_in_tiles = 0;
> +                for (; ctb_x < subpic_r && tile_x <
> pps->num_tile_columns; tile_x++) {
> +                    ctb_x += pps->col_width_val[tile_x];
> +                    width_in_tiles++;
> +                }
> +
> +                if (entropy_sync)
> +                    height = sps->sps_subpic_height_minus1[slice_idx] + 1;
> +                else {
> +                    const int height_in_ctus =
> sps->sps_subpic_height_minus1[slice_idx] + 1;
> +                    const int subpic_t =
> sps->sps_subpic_ctu_top_left_y[slice_idx];
> +                    const int subpic_b = subpic_t + height_in_ctus;
> +
> +                    int ctb_y = 0, tile_y = 0, height_in_tiles;
> +                    for (; ctb_y < subpic_t && tile_y <
> pps->num_tile_rows; tile_y++)
> +                        ctb_y += pps->row_height_val[tile_y];
> +
> +                    height_in_tiles = 0;
> +                    for (; ctb_y < subpic_b && tile_y <
> pps->num_tile_rows; tile_y++) {
> +                        ctb_y += pps->row_height_val[tile_y];
> +                        height_in_tiles++;
> +                    }
>
Hi Frank,
Thank you for the v2.
Same logic as width_in_tiles, with only a few different parameters. Better
to avoid duplication.
How about using a single function: size_in_tiles(size_in_ctu, top_left,
tile_val, num_tile)?

> +
> +                    height = height_in_tiles;
> +                }
> +            } else {
> +                width_in_tiles =
> +                    pps->pps_slice_width_in_tiles_minus1[slice_idx] + 1;
> +
> +                if (entropy_sync)
> +                    height = pps->slice_height_in_ctus[slice_idx];
> +                else
> +                    height =
> pps->pps_slice_height_in_tiles_minus1[slice_idx] + 1;
> +            }
>
>              current->num_entry_points = width_in_tiles * height;
>          } else {
> --
> 2.47.0
>
>
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