Re: [FFmpeg-devel] [PATCH v2] lavc/vp9: reset segmentation fields when segmentation isn't enabled

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

llyyr.public@gmail.com:
> From: llyyr <llyyr.public@gmail.com>
> 
> Fields under the segmentation switch are never reset on a new frame, and
> retain the value from the previous frame. This bugs out a bunch of
> hwaccel drivers when segmentation is disabled but update_map isn't
> reset because they don't ignore values behind switches. This commit also
> resets the temporal field, though it may not be required.
> 
> We also do this for vp8 [1] so this commit is just mirroring the vp8
> logic.
> 
> This fixes an issue with certain samples [2] that causes blocky
> artifacts with vaapi, d3d11va and cuda (and possibly others).
> Mesa worked around [3] this by ignoring these fields if
> segmentation.enabled is 0, but d3d11va still displays blocky artifacts.
> 
> [1] https://git.ffmpeg.org/gitweb/ffmpeg.git/blob/HEAD:/libavcodec/vp8.c#l811

You should probably not link to HEAD here, because the line number will
be wrong in the future.

> [2] https://github.com/mpv-player/mpv/issues/13533
> [3] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27816
> 
> Signed-off-by: llyyr <llyyr.public@gmail.com>
> ---
>  libavcodec/vp9.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/libavcodec/vp9.c b/libavcodec/vp9.c
> index 6e2d18bf9595..8ede2e2eb358 100644
> --- a/libavcodec/vp9.c
> +++ b/libavcodec/vp9.c
> @@ -709,6 +709,12 @@ static int decode_frame_header(AVCodecContext *avctx,
>                  s->s.h.segmentation.feat[i].skip_enabled = get_bits1(&s->gb);
>              }
>          }
> +    } else {
> +        // Reset fields under segmentation switch if segmentation is disabled.
> +        // This is necessary because some hwaccels don't ignore these fields
> +        // if segmentation is disabled.
> +        s->s.h.segmentation.temporal = 0;
> +        s->s.h.segmentation.update_map = 0;
>      }
>  
>      // set qmul[] based on Y/UV, AC/DC and segmentation Q idx deltas

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