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

[Frank Plowman <post@frankplowman.com>]

On 09/04/2024 14:36, Nuo Mi wrote:
> 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 state is no longer valid, right?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.

I see, my mistake.  Yes in this case I do not think sps_id_used must be
explicitly reset.

-- 
Frank
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