Re: [FFmpeg-devel] [PATCH] lavc/vaapi_h264: Fix merging fields in DPB with missing references

[Mark Thompson <sw@jkqxz.net>]

On 07/05/2024 07:00, David Rosca wrote:
> If there are missing references, h264 decode does error concealment
> by copying previous refs which means there will be duplicated surfaces
> and this code would try to merge them instead of correctly appending
> to DPB. Make sure the fields were actually merged before early return.
> ---
>  libavcodec/vaapi_h264.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/vaapi_h264.c b/libavcodec/vaapi_h264.c
> index b47531ce1c..c62a320e97 100644
> --- a/libavcodec/vaapi_h264.c
> +++ b/libavcodec/vaapi_h264.c
> @@ -112,8 +112,9 @@ static int dpb_add(DPB *dpb, const H264Picture *pic)
>                  } else {
>                      va_pic->BottomFieldOrderCnt = temp_va_pic.BottomFieldOrderCnt;
>                  }
> +                return 0;
>              }
> -            return 0;
> +            break;
>          }
>      }
>  

I agree that the old code did nasty things, but can you explain a bit more about the reasoning for what you've got now?

I'm thinking that given duplication a top field could appear twice, so you'd want to merge twice if you have the matching bottom field.

Thanks,

- Mark
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