[FFmpeg-devel] [PATCH] avcodec/vvc decode: ALF filtering without CC-ALF

[Nuo Mi]

Hi Chris and Frank,
Thank you for the patch and review.

On Mon, Dec 2, 2024 at 10:27 PM Chris Warrington via ffmpeg-devel <
ffmpeg-devel at ffmpeg.org> wrote:

> When a stream has ALF filtering enabled but not CC-ALF, the CC-ALF set
> indexes alf->ctb_cc_idc are being read uninitialized during ALF filtering.
>
> This change initializes alf->ctb_cc_idc whenever ALF is enabled.
>
> Ref. https://trac.ffmpeg.org/ticket/11325
>
> ---
>  libavcodec/vvc/ctu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/vvc/ctu.c b/libavcodec/vvc/ctu.c
> index a32abdeb62..c972dcc33e 100644
> --- a/libavcodec/vvc/ctu.c
> +++ b/libavcodec/vvc/ctu.c
> @@ -2288,6 +2288,7 @@ static void alf_params(VVCLocalContext *lc, const
> int rx, const int ry)
>      ALFParams *alf                = &CTB(fc->tab.alf, rx, ry);
>
>      alf->ctb_flag[LUMA] = alf->ctb_flag[CB] = alf->ctb_flag[CR] = 0;
> +    alf->ctb_cc_idc[0] = alf->ctb_cc_idc[1] = 0;
>
This will introduce two writes for all blocks, even if there is no CC ALF.
How about checking the sps_ccalf_enabled_flag in ff_vvc_alf_filter?

>      if (sh->sh_alf_enabled_flag) {
>          alf->ctb_flag[LUMA] = ff_vvc_alf_ctb_flag(lc, rx, ry, LUMA);
>          if (alf->ctb_flag[LUMA]) {
> @@ -2318,7 +2319,6 @@ static void alf_params(VVCLocalContext *lc, const
> int rx, const int ry)
>          const uint8_t cc_enabled[] = { sh->sh_alf_cc_cb_enabled_flag,
> sh->sh_alf_cc_cr_enabled_flag };
>          const uint8_t cc_aps_id[]  = { sh->sh_alf_cc_cb_aps_id,
> sh->sh_alf_cc_cr_aps_id };
>          for (int i = 0; i < 2; i++) {
> -            alf->ctb_cc_idc[i] = 0;
>              if (cc_enabled[i]) {
>                  const VVCALF *aps = fc->ps.alf_list[cc_aps_id[i]];
>                  alf->ctb_cc_idc[i] = ff_vvc_alf_ctb_cc_idc(lc, rx, ry, i,
> aps->num_cc_filters[i]);
> --
> 2.43.0
>
>
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