[FFmpeg-devel] [PATCH v6 4/9] avcodec: add cbs for h266/vvc

[Mark Thompson]

On 18/02/2021 15:20, Nuo Mi wrote:
>>
>>>> +                return AVERROR(ENOMEM);
>>>> +        }
>>>> +        h266->ph = (H266RawPH*)h266->ph_ref->data;
>>>> +        memcpy(h266->ph, &current->sh_picture_header,
>>> sizeof(H266RawPH));
>>>
>>> This memcpy() is naughty - if that was a ref to a previous picture header
>>> then you've just overwritten the reference while the other unit still holds
>>> it.
>>>
>>> If the slice is unit->content then unit->content_ref is a reference to a
>>> superstructure of the picture header, avoiding the copy, but I'm not sure
>>> it's the right way to do it.
>>>
>>> Is it right that the two possible options here are:
>>> * Store a ref, which might be to a newly-allocated buffer or might be to
>>> a previous unit.
>>>
>> * Store the whole structure in the private context.
>>>
>> ?
>>>
>>> If the structure isn't too large, then the second option feels much
>>> simpler.
>>>
>>> If it is large such that holding references and avoiding copies is
>>> beneficial (which is quite large, every ref entails a malloc/free
>>> call-pair), then we probably want that ref to always be to the unit?
>>>
>> If we store the whole structure, it's hard to detect the picture header
>> missing case.
>>
> Also, if we use this as start point of the native decoder, the native
> decoder may need ref the picture header for multi-thread decoding.

I think it would be reffing all of the units of the picture, which would include the picture header.

- Mark