[FFmpeg-devel] [PATCH 5/6] avcodec/h264: Avoid using gray gap frames as references

[James Almer]

On 11/14/2023 2:20 PM, Michael Niedermayer wrote:
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>   libavcodec/h264_refs.c | 11 +++++++++++
>   libavcodec/h264dec.c   |  1 +
>   libavcodec/h264dec.h   |  1 +
>   3 files changed, 13 insertions(+)
> 
> diff --git a/libavcodec/h264_refs.c b/libavcodec/h264_refs.c
> index 92778e737a5..9bc7b20988f 100644
> --- a/libavcodec/h264_refs.c
> +++ b/libavcodec/h264_refs.c
> @@ -410,6 +410,17 @@ int ff_h264_build_ref_list(H264Context *h, H264SliceContext *sl)
>                   else
>                       return -1;
>               }
> +            if (h->noref_gray>0 && sl->ref_list[list][index].parent->gray && h->non_gray) {
> +                for (int j=0; j<sl->list_count; j++) {
> +                    int list2 = (list+j)&1;
> +                    if (h->default_ref[list2].parent && !h->default_ref[list2].parent->gray
> +                        && !(!FIELD_PICTURE(h) && (h->default_ref[list2].reference&3) != 3)) {
> +                        sl->ref_list[list][index] = h->default_ref[list2];
> +                        av_log(h, AV_LOG_DEBUG, "replacement of gray gap frame\n");
> +                        break;
> +                    }
> +                }
> +            }
>               av_assert0(av_buffer_get_ref_count(sl->ref_list[list][index].parent->f->buf[0]) > 0);
>           }
>       }
> diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
> index 7ea55db75dd..b48821db244 100644
> --- a/libavcodec/h264dec.c
> +++ b/libavcodec/h264dec.c
> @@ -1091,6 +1091,7 @@ static const AVOption h264_options[] = {
>       { "nal_length_size", "nal_length_size", OFFSET(nal_length_size), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 4, VDX },
>       { "enable_er", "Enable error resilience on damaged frames (unsafe)", OFFSET(enable_er), AV_OPT_TYPE_BOOL, { .i64 = -1 }, -1, 1, VD },
>       { "x264_build", "Assume this x264 version if no x264 version found in any SEI", OFFSET(x264_build), AV_OPT_TYPE_INT, {.i64 = -1}, -1, INT_MAX, VD },
> +    { "noref_gray", "Avoid using gray gap frames as references", OFFSET(noref_gray), AV_OPT_TYPE_INT, {.i64 = 1}, -1, 1, VD },

Should be AV_OPT_TYPE_BOOL, and there's no point allowing -1. That's 
only useful for example when used with external modules as "use the 
default from the external library".

>       { NULL },
>   };
>   
> diff --git a/libavcodec/h264dec.h b/libavcodec/h264dec.h
> index 366626c056c..591769ab258 100644
> --- a/libavcodec/h264dec.h
> +++ b/libavcodec/h264dec.h
> @@ -571,6 +571,7 @@ typedef struct H264Context {
>       int ref2frm[MAX_SLICES][2][64];     ///< reference to frame number lists, used in the loop filter, the first 2 are for -2,-1
>   
>       int non_gray;                       ///< Did we encounter a intra frame after a gray gap frame
> +    int noref_gray;
>   } H264Context;
>   
>   extern const uint16_t ff_h264_mb_sizes[4];