[FFmpeg-devel] [PATCH] avcodec/cbs_h266: Fix regression in DVB clip introduced by 93281630a71c06642adfebebb0d4b105a4e02e91

[Nuo Mi]

On Mon, Nov 11, 2024 at 4:27 AM Frank Plowman <post at frankplowman.com> wrote:

>
>
> On 10/11/2024 12:13, Nuo Mi wrote:
> > This commit introduced a regression to
> VVC_HDR_UHDTV1_OpenGOP_3840x2160_50fps_HLG10_mosaic.ts.
> >
> > Root Cause:
> > The AV_CEIL_RSHIFT(a, b) macro uses bit tricks that work only when -a is
> a negative value.
> > However, due to integer promotion rules, this behavior does not extend
> to the unsigned int type.
> >
> > See "6.3.1.1 Boolean, characters, and integers" in the "ISO/IEC 9899"
> for details.
> >
> > Reported-by: Frank Plowman <post at frankplowman.com>
> > ---
> >  libavcodec/cbs_h266_syntax_template.c | 12 ++++++------
> >  1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/libavcodec/cbs_h266_syntax_template.c
> b/libavcodec/cbs_h266_syntax_template.c
> > index b21d07491b..6b2d6534ef 100644
> > --- a/libavcodec/cbs_h266_syntax_template.c
> > +++ b/libavcodec/cbs_h266_syntax_template.c
> > @@ -1162,7 +1162,7 @@ static int FUNC(sps)(CodedBitstreamContext *ctx,
> RWContext *rw,
> >              for (i = 1; i <= current->sps_num_subpics_minus1; i++) {
> >                  if (!current->sps_subpic_same_size_flag) {
> >                      if (current->sps_pic_width_max_in_luma_samples >
> ctb_size_y) {
> > -                        const unsigned int win_right_edge =
> > +                        const int win_right_edge =
> >                              current->sps_pic_width_max_in_luma_samples
> >                            - current->sps_conf_win_right_offset *
> sub_width_c;
> >                          us(wlen, sps_subpic_ctu_top_left_x[i], 0,
> > @@ -1172,7 +1172,7 @@ static int FUNC(sps)(CodedBitstreamContext *ctx,
> RWContext *rw,
> >                          infer(sps_subpic_ctu_top_left_x[i], 0);
> >                      if (current->sps_pic_height_max_in_luma_samples >
> >                          ctb_size_y) {
> > -                        const unsigned int win_bottom_edge =
> > +                        const int win_bottom_edge =
> >                              current->sps_pic_height_max_in_luma_samples
> >                            - current->sps_conf_win_bottom_offset *
> sub_height_c;
> >                          us(hlen, sps_subpic_ctu_top_left_y[i], 0,
> > @@ -1183,9 +1183,9 @@ static int FUNC(sps)(CodedBitstreamContext *ctx,
> RWContext *rw,
> >                      if (i < current->sps_num_subpics_minus1 &&
> >                          current->sps_pic_width_max_in_luma_samples >
> >                          ctb_size_y) {
> > -                        const unsigned int win_left_edge =
> > +                        const int win_left_edge =
> >                              current->sps_conf_win_left_offset *
> sub_width_c;
> > -                        const unsigned int win_left_edge_ctus =
> > +                        const int win_left_edge_ctus =
> >                              AV_CEIL_RSHIFT(win_left_edge,
> ctb_log2_size_y);
> >                          us(wlen, sps_subpic_width_minus1[i],
> >                             win_left_edge_ctus >
> current->sps_subpic_ctu_top_left_x[i]
> > @@ -1200,9 +1200,9 @@ static int FUNC(sps)(CodedBitstreamContext *ctx,
> RWContext *rw,
> >                      if (i < current->sps_num_subpics_minus1 &&
> >                          current->sps_pic_height_max_in_luma_samples >
> >                          ctb_size_y) {
> > -                        const unsigned int win_top_edge =
> > +                        const int win_top_edge =
> >                              current->sps_conf_win_top_offset *
> sub_height_c;
> > -                        const unsigned int win_top_edge_ctus =
> > +                        const int win_top_edge_ctus =
> >                              AV_CEIL_RSHIFT(win_top_edge,
> ctb_log2_size_y);
> >                          us(hlen, sps_subpic_height_minus1[i],
> >                             win_top_edge_ctus >
> current->sps_subpic_ctu_top_left_y[i]
>
> LGTM!
>
Thank you. Frank.
Merged and backported to 7.1 with help from James

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