[FFmpeg-devel] libavc/libx264: add support to propagate SSE values through encoder stats

[Anton Khirnov]

Quoting Carotti, Elias via ffmpeg-devel (2023-10-11 12:54:21)
> diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
> index 77a9f173b4..85bd870f5d 100644
> --- a/libavcodec/libx264.c
> +++ b/libavcodec/libx264.c
> @@ -726,7 +726,39 @@ FF_ENABLE_DEPRECATION_WARNINGS
> 
>      pkt->flags |= AV_PKT_FLAG_KEY*pic_out.b_keyframe;
>      if (ret) {
> -        ff_side_data_set_encoder_stats(pkt, (pic_out.i_qpplus1 - 1) * FF_QP2LAMBDA, NULL, 0, pict_type);
> +        const AVPixFmtDescriptor *pix_desc = av_pix_fmt_desc_get(csp_to_pixfmt(pic_out.img.i_csp));

There's a problem here - we do not handle all values of i_csp.
E.g. we have no equivalent of X264_CSP_NV12 | X264_CSP_HIGH_DEPTH, which
x264 will use for YUV420P10 input.

The best solution is probably to use AVCodecContext.pix_fmt and assume
that x264 doesn't do any nontrivial (i.e. other than interleaving and
such) pixel format transformations internally.

> +        int error_count = 0;
> +        int64_t *errors = NULL;
> +        int64_t sse[3] = {0};
> +
> +        if (ctx->flags & AV_CODEC_FLAG_PSNR) {
> +            double scale[3] = { 1,
> +                (double)(1 << pix_desc->log2_chroma_h) * (1 << pix_desc->log2_chroma_w),
> +                (double)(1 << pix_desc->log2_chroma_h) * (1 << pix_desc->log2_chroma_w),
> +            };
> +
> +            error_count = pix_desc->nb_components;
> +
> +            av_log(ctx, AV_LOG_DEBUG, "PSNR values from libx264: %.3f %.3f %.3f.\n",
> +                   pic_out.prop.f_psnr[0], pic_out.prop.f_psnr[1], pic_out.prop.f_psnr[2]);

In my tests libx264 prints these values by itself, so this seems
redundant.

-- 
Anton Khirnov