[FFmpeg-devel] [PATCH] lavc/vvc: Error pps_single_slice_per_subpic_flag

[Nuo Mi]

On Sat, Feb 3, 2024 at 9:54 PM Frank Plowman <post at frankplowman.com> wrote:

> On 02/02/2024 14:39, Nuo Mi wrote:
> > On Thu, Feb 1, 2024 at 10:01 PM <post at frankplowman.com> wrote:
> >
> >> From: Frank Plowman <post at frankplowman.com>
> >>
> >> pps_single_slice_per_subpic_flag is not yet supported.  Support is WIP,
> >> but in the meantime throw an error when trying to decode a bitstream
> >> with it set, avoiding an out-of-bounds array access.
> >>
> >> Fixes: out-of-bounds array access for conformance bitstreams
> >> SUBPIC_C_ERICSSON_1, SUBPIC_D_ERICSSON_1, MNUT_A_Nokia_4 and
> >> MNUT_B_Nokia_3.
> >>
> >> Signed-off-by: Frank Plowman <post at frankplowman.com>
> >> ---
> >>   libavcodec/vvc/vvc_ps.c | 21 ++++++++++++++++-----
> >>   1 file changed, 16 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/libavcodec/vvc/vvc_ps.c b/libavcodec/vvc/vvc_ps.c
> >> index 2cf156b323..bd81d70e71 100644
> >> --- a/libavcodec/vvc/vvc_ps.c
> >> +++ b/libavcodec/vvc/vvc_ps.c
> >> @@ -381,11 +381,16 @@ static void pps_multi_tiles_slice(VVCPPS *pps,
> const
> >> int tile_idx, const int i,
> >>       }
> >>   }
> >>
> >> -static void pps_rect_slice(VVCPPS* pps)
> >> +static int pps_rect_slice(VVCPPS* pps)
> >>   {
> >>       const H266RawPPS* r = pps->r;
> >>       int tile_idx = 0, off = 0;
> >>
> >> +    if (r->pps_single_slice_per_subpic_flag) {
> >> +        avpriv_report_missing_feature(NULL,
> >> "pps_single_slice_per_subpic_flag");
> >> +        return AVERROR_PATCHWELCOME;
> >> +    }
> >> +
> >>       for (int i = 0; i < r->pps_num_slices_in_pic_minus1 + 1; i++) {
> >>           if (!r->pps_slice_width_in_tiles_minus1[i] &&
> >>               !r->pps_slice_height_in_tiles_minus1[i]) {
> >> @@ -396,9 +401,11 @@ static void pps_rect_slice(VVCPPS* pps)
> >>           }
> >>           tile_idx = next_tile_idx(tile_idx, i, r);
> >>       }
> >> +
> >> +    return 0;
> >>   }
> >>
> >> -static void pps_no_rect_slice(VVCPPS* pps)
> >> +static int pps_no_rect_slice(VVCPPS* pps)
> >>   {
> >>       const H266RawPPS* r = pps->r;
> >>       int ctu_x, ctu_y, off = 0;
> >> @@ -409,20 +416,24 @@ static void pps_no_rect_slice(VVCPPS* pps)
> >>               pps_add_ctus(pps, &off, ctu_x, ctu_y,
> >> r->col_width_val[tile_x], r->row_height_val[tile_y]);
> >>           }
> >>       }
> >> +
> >> +    return 0;
> >>   }
> >>
> >>   static int pps_slice_map(VVCPPS *pps)
> >>   {
> >> +    int ret;
> >> +
> >>       pps->ctb_addr_in_slice = av_calloc(pps->ctb_count,
> >> sizeof(*pps->ctb_addr_in_slice));
> >>       if (!pps->ctb_addr_in_slice)
> >>           return AVERROR(ENOMEM);
> >>
> >>       if (pps->r->pps_rect_slice_flag)
> >> -        pps_rect_slice(pps);
> >> +        ret = pps_rect_slice(pps);
> >>       else
> >> -        pps_no_rect_slice(pps);
> >> +        ret = pps_no_rect_slice(pps);
> >>
> >> -    return 0;
> >> +    return ret;
> >>   }
> >>
> > Thank you Frank. This changed  too much code.
> > How about we only check the sps_num_subpics_minus1 in decode_sps.
>
> I wrote it like this so that the avpriv_report_missing_feature is where
> the feature would need to be, helping readability and searchability.

We need to make changes to both the cbs and the decoder for subpic support.
pps_slice_map is not the first place.

> I
> could remove the return from pps_rect_slice and pps_no_rect_slice which
> would get rid of a handful of changed lines but the changes are trivial
> so it is not a big deal imo.
>
Once we implemented subpic, both pps_rect_slice and pps_no_rect_slice are
not supposed to return a value. We need to change it back


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