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

[Frank Plowman]

Hi both,

Can we push either of these?  Someone else has reported the same issue
on Trac (#11325).  The difference between the two proposed
implementations seems rather superficial to me.

Thanks and happy new year,
Frank

On 03/12/2024 02:17, Nuo Mi wrote:
> 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]);
>> --