On Sun, Oct 6, 2024 at 6:49 AM Frank Plowman <p...@frankplowman.com> wrote:
> H.266 (V3) section 6.3.3 dictates that the division of the picture into
> subpictures must be exhaustive and mutually exclusive, i.e. that each
> CTU "belongs to" one and only one subpicture. In most cases this is
> guaranteed by the syntax, but in the case sps_subpic_same_size_flag=0,
> we must check this is true ourselves.
>
> Signed-off-by: Frank Plowman <p...@frankplowman.com>
> ---
> libavcodec/cbs_h266_syntax_template.c | 46 +++++++++++++++++++++++++--
> 1 file changed, 44 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/cbs_h266_syntax_template.c
> b/libavcodec/cbs_h266_syntax_template.c
> index b4165b43b3..822ee26f46 100644
> --- a/libavcodec/cbs_h266_syntax_template.c
> +++ b/libavcodec/cbs_h266_syntax_template.c
> @@ -1191,7 +1191,7 @@ static int FUNC(sps)(CodedBitstreamContext *ctx,
> RWContext *rw,
> win_left_edge_ctus >
> current->sps_subpic_ctu_top_left_x[i]
> ? win_left_edge_ctus -
> current->sps_subpic_ctu_top_left_x[i]
> : 0,
> - MAX_UINT_BITS(wlen), 1, i);
> + tmp_width_val -
> current->sps_subpic_ctu_top_left_x[i] - 1, 1, i);
> } else {
> infer(sps_subpic_width_minus1[i],
> tmp_width_val -
> @@ -1208,7 +1208,7 @@ static int FUNC(sps)(CodedBitstreamContext *ctx,
> RWContext *rw,
> win_top_edge_ctus >
> current->sps_subpic_ctu_top_left_y[i]
> ? win_top_edge_ctus -
> current->sps_subpic_ctu_top_left_y[i]
> : 0,
> - MAX_UINT_BITS(hlen), 1, i);
> + tmp_height_val -
> current->sps_subpic_ctu_top_left_y[i] - 1, 1, i);
> } else {
> infer(sps_subpic_height_minus1[i],
> tmp_height_val -
> @@ -1242,6 +1242,48 @@ static int FUNC(sps)(CodedBitstreamContext *ctx,
> RWContext *rw,
> infer(sps_loop_filter_across_subpic_enabled_flag[i],
> 0);
> }
> }
> + // If the subpic partitioning structure is signalled
> explicitly,
> + // validate it constitutes an exhaustive and mutually
> exclusive
> + // coverage of the picture, per 6.3.3. If the partitioning
> is not
> + // provided explicitly, then it is ensured by the syntax and
> we need
> + // not check.
> + if (!current->sps_subpic_same_size_flag) {
> + char *ctu_in_subpic = av_mallocz(tmp_width_val *
> tmp_height_val);
>
Thank you for the patch.
The slices will cover the entire subpicture without any overlap, and the
CTUs will cover the entire slice without any overlap.
We will check num_slices_in_subpic[] in FUNC(pps). How about summing all
the values in num_slices_in_subpic[] and verifying if it equals
sps_num_subpics_minus1 + 1?
+ if (!ctu_in_subpic)
> + return AVERROR(ENOMEM);
> + for (i = 0; i <= current->sps_num_subpics_minus1; i++) {
> + const unsigned x0 =
> current->sps_subpic_ctu_top_left_x[i];
> + const unsigned y0 =
> current->sps_subpic_ctu_top_left_y[i];
> + const unsigned w =
> current->sps_subpic_width_minus1[i] + 1;
> + const unsigned h =
> current->sps_subpic_height_minus1[i] + 1;
> + av_assert0(x0 + w - 1 < tmp_width_val);
> + av_assert0(y0 + h - 1 < tmp_height_val);
> + for (unsigned x = x0; x < x0 + w; x++) {
> + for (unsigned y = y0; y < y0 + h; y++) {
> + const unsigned idx = y * tmp_width_val + x;
> + if (ctu_in_subpic[idx]) {
> + av_log(ctx->log_ctx, AV_LOG_ERROR,
> + "Subpictures overlap.\n");
> + av_freep(&ctu_in_subpic);
> + return AVERROR_INVALIDDATA;
> + }
> + ctu_in_subpic[idx] = 1;
> + }
> + }
> + }
> + for (unsigned x = 0; x < tmp_width_val; x++) {
> + for (unsigned y = 0; y < tmp_height_val; y++) {
> + const unsigned idx = y * tmp_width_val + x;
> + if (!ctu_in_subpic[idx]) {
> + av_log(ctx->log_ctx, AV_LOG_ERROR,
> + "Subpictures do not cover the entire
> picture.\n");
> + av_freep(&ctu_in_subpic);
> + return AVERROR_INVALIDDATA;
> + }
> + }
> + }
> + av_freep(&ctu_in_subpic);
> + }
> } else {
> infer(sps_subpic_ctu_top_left_x[0], 0);
> infer(sps_subpic_ctu_top_left_y[0], 0);
> --
> 2.46.2
>
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