Re: [FFmpeg-devel] [PATCH 1/2] lavc/vvc: Fix NumEntryPoints derivation

[Frank Plowman <post@frankplowman.com>]

On 02/03/2025 12:41, Nuo Mi wrote:
> On Sun, Feb 23, 2025 at 8:05 PM Frank Plowman <post@frankplowman.com> wrote:
> 
>> If pps_single_slice_per_subpic_flag is 1,
>> slice_{width,height}_in_ctus 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>
>> ---
>>  libavcodec/cbs_h266_syntax_template.c | 34 ++++++++++++++++++++++-----
>>  1 file changed, 28 insertions(+), 6 deletions(-)
>>
>> diff --git a/libavcodec/cbs_h266_syntax_template.c
>> b/libavcodec/cbs_h266_syntax_template.c
>> index 58211026bb..b84f3e29db 100644
>> --- a/libavcodec/cbs_h266_syntax_template.c
>> +++ b/libavcodec/cbs_h266_syntax_template.c
>> @@ -3440,13 +3440,35 @@ 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
>> +                    height =
>> pps->pps_slice_height_in_tiles_minus1[slice_idx] + 1;
>>
>   pps_slice_height_in_tiles_minus1 is also undefined if
> pps_single_slice_per_subpic_flag is true.

Good catch!  Fixed in v2.

Thanks,
Frank

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