Re: [FFmpeg-devel] [PATCH] avcodec/vvc/ps: reset sps_id_used on PS uninit

[Nuo Mi <nuomi2021@gmail.com>]

On Mon, Apr 8, 2024 at 11:15 PM Frank Plowman <post@frankplowman.com> wrote:

> On 08/04/2024 15:12, Nuo Mi wrote:
> > On Mon, Apr 8, 2024 at 4:37 PM Frank Plowman <post@frankplowman.com>
> wrote:
> >
> >> On 07/04/2024 15:48, James Almer wrote:
> >>> On 4/7/2024 10:38 AM, Nuo Mi wrote:
> >>>> On Sun, Apr 7, 2024 at 11:05 AM James Almer <jamrial@gmail.com>
> wrote:
> >>>>
> >>>>> Signed-off-by: James Almer <jamrial@gmail.com>
> >>>>> ---
> >>>>>   libavcodec/vvc/ps.c | 1 +
> >>>>>   1 file changed, 1 insertion(+)
> >>>>>
> >>>>> diff --git a/libavcodec/vvc/ps.c b/libavcodec/vvc/ps.c
> >>>>> index 3c71c34bae..83ee75fb62 100644
> >>>>> --- a/libavcodec/vvc/ps.c
> >>>>> +++ b/libavcodec/vvc/ps.c
> >>>>> @@ -912,6 +912,7 @@ void ff_vvc_ps_uninit(VVCParamSets *ps)
> >>>>>           ff_refstruct_unref(&ps->sps_list[i]);
> >>>>>       for (int i = 0; i < FF_ARRAY_ELEMS(ps->pps_list); i++)
> >>>>>           ff_refstruct_unref(&ps->pps_list[i]);
> >>>>> +    ps->sps_id_used = 0;
> >>>>>
> >>>> Hi James,
> >>>> thank you for the patch.
> >>>>
> >>>> Is this really necessary?
> >>>> vvc_ps_uninit will be called by vvc_decode_free,
> >>>> We are not supposed to use any member of VVCParamSets after
> >>>> vvc_decode_free.
> >>>
> >>> My bad, i thought it was also called on every flush() call.
> >>>
> >>> Something like the following:
> >>>
> >>>> diff --git a/libavcodec/vvc/dec.c b/libavcodec/vvc/dec.c
> >>>> index eb447604fe..463536512e 100644
> >>>> --- a/libavcodec/vvc/dec.c
> >>>> +++ b/libavcodec/vvc/dec.c
> >>>> @@ -963,6 +963,8 @@ static av_cold void
> >>>> vvc_decode_flush(AVCodecContext *avctx)
> >>>>          ff_vvc_flush_dpb(last);
> >>>>      }
> >>>>
> >>>> +    s->ps->sps_id_used = 0;
> >>>> +
> >>>>      s->eos = 1;
> >>>>  }
> >>>
> >>> Should be done on FFCodec.flush() (like when seeking) as the previous
> >>> state is no longer valid, right?
> >>
> >> Yes I agree, I think this is needed.  Cases where the random access
> >> point has no leading pictures should be covered by the existing logic as
> >> these always fall at the start of a CVS, but I think this is needed to
> >> cover the case in which there are leading pictures.
> >>
> > This patch isn't necessary.
> > Leading pictures won't carry SPS.
> > IDR, CRA, and GDR will carry SPS, but they will also start a new CVS,
> which
> > will covered by the current logic.
> >
>
> I may be misunderstanding the spec, NoOutputBeforeRecoveryFlag is set
> for pictures which have no leading pictures, no?  In any case take, for
> instance, a CRA picture.  In most cases, CRA pictures have
> NoOutputBeforeRecoveryFlag=0, therefore are not CLVSS pictures and
> sps_id_used is not reset by the existing logic.  Do we not need to reset
> sps_id_used when seeking to a CRA then?
>
After seeking, we'll set s->last_eos to 1.
For a CRA, decode_recovery_flag will set s->no_output_before_recovery_flag
to s->last_eos.
So no_output_before_recovery_flag will be 1, not 0.

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