[FFmpeg-devel] [PATCH] avcodec/h264_refs: reset MMCO when invalid mmco code is found

[Paul B Mahol]

On 12/9/18, Mark Thompson <sw at jkqxz.net> wrote:
> On 09/12/2018 08:52, Paul B Mahol wrote:
>> On 12/7/18, Paul B Mahol <onemda at gmail.com> wrote:
>>> On 12/7/18, Michael Niedermayer <michael at niedermayer.cc> wrote:
>>>> On Fri, Dec 07, 2018 at 10:36:23AM +0100, Paul B Mahol wrote:
>>>>> On 12/7/18, Paul B Mahol <onemda at gmail.com> wrote:
>>>>>> On 12/7/18, Michael Niedermayer <michael at niedermayer.cc> wrote:
>>>>>>> On Thu, Dec 06, 2018 at 03:26:41PM +0100, Paul B Mahol wrote:
>>>>>>>> This recovers state with #7374 linked sample.
>>>>>>>>
>>>>>>>> Work funded by Open Broadcast Systems.
>>>>>>>>
>>>>>>>> Signed-off-by: Paul B Mahol <onemda at gmail.com>
>>>>>>>> ---
>>>>>>>>  libavcodec/h264_refs.c | 2 +-
>>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/libavcodec/h264_refs.c b/libavcodec/h264_refs.c
>>>>>>>> index eaf965e43d..5645a203a7 100644
>>>>>>>> --- a/libavcodec/h264_refs.c
>>>>>>>> +++ b/libavcodec/h264_refs.c
>>>>>>>> @@ -718,6 +718,7 @@ int ff_h264_execute_ref_pic_marking(H264Context
>>>>>>>> *h)
>>>>>>>>              }
>>>>>>>>              break;
>>>>>>>>          case MMCO_RESET:
>>>>>>>> +        default:
>>>>>>>>              while (h->short_ref_count) {
>>>>>>>>                  remove_short(h, h->short_ref[0]->frame_num, 0);
>>>>>>>>              }
>>>>>>>> @@ -730,7 +731,6 @@ int ff_h264_execute_ref_pic_marking(H264Context
>>>>>>>> *h)
>>>>>>>>              for (j = 0; j < MAX_DELAYED_PIC_COUNT; j++)
>>>>>>>>                  h->last_pocs[j] = INT_MIN;
>>>>>>>>              break;
>>>>>>>> -        default: assert(0);
>>>>>>>>          }
>>>>>>>>      }
>>>>>>>
>>>>>>> mmco[i].opcode should not be invalid, its checked around the point
>>>>>>> where
>>>>>>> this
>>>>>>> array is filled.
>>>>>>> unless there is something iam missing
>>>>>>
>>>>>> Yes, you are missing big time.
>>>>>> If you think by "checked" about those nice asserts they are not
>>>>>> enabled
>>>>>> at
>>>>>> all.
>>>>>>
>>>>>
>>>>> There is check for invalid opcode, but stored invalid opcode is not
>>>>> changed.
>>>>
>>>> Theres no question that we end with a invalid value in the struct, but
>>>> that
>>>> is not intended to be in there. You can see that this is not intended by
>>>> simply looking at the variable that holds the number of entries, it is
>>>> not written at all in this case.
>>>>
>>>> So for example if this code stores 5 correct looking mmcos and the 6th
>>>> is
>>>> invalid, 6 are in the array but the number of entries is just left where
>>>> it
>>>> was, that could be maybe 3 or 8 or 1. Just "defaulting out" the invalid
>>>> value
>>>> later doesnt feel ideal.
>>>
>>> Nope, mmco state is left in inconsistent state, and my patch fix it. As
>>> you
>>> provided nothing valuable to consider as alternative I will apply it.
>>>
>>
>> What about converting any invalid mmco opcode to mmco reset and
>> updating mmco size too?
>> Currently mmco size is left in previous state.
>
> Don't invent a new RESET (= 5) operation - that type is special and its
> presence implies other constraints which we probably don't want to think
> about here (around frame_num in particular).
>
> I think END / truncating the list would be best option?
>

Nope, that would still put it into bad state. With your approach decoder does
not recover from artifacts. Try sample from bug report #7374.