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

["Carotti, Elias via ffmpeg-devel" <ffmpeg-devel@ffmpeg.org>]

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On Fri, 2023-10-13 at 16:16 +0200, Anton Khirnov wrote:
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> 
> 
> 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.
> 


I see. Wouldn't not outputting the SSE values when csp_to_pixfmt()
returns AV_PIX_FMT_NONE work better? 
That wouldn't be worse than it is today (meaning that right now we
don't get those values for any pix_fmt).
Anyway, I did as you suggested and used AVCodecContext.pix_fmt.


> > <snip>
> > +            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.

removed.




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From b702fcd76cf0626f75a941875f31add50d08894d Mon Sep 17 00:00:00 2001
From: Elias Carotti <eliascrt _at_ amazon _dot_ .it>
Date: Fri, 15 Sep 2023 20:05:43 +0200
Subject: [PATCH] avcodec/libx264: Add the SSE computation for libx264.

Since libx264 only provides a per-frame per-channel PSNR, this is inverted to get back the SSE.
---
 libavcodec/libx264.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
index 77a9f173b4..6ebe210039 100644
--- a/libavcodec/libx264.c
+++ b/libavcodec/libx264.c
@@ -726,7 +726,36 @@ 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(ctx->pix_fmt);
+        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;
+
+            for (int i = 0; i < pix_desc->nb_components; ++i) {
+                double max_value = (double)(1 << pix_desc->comp[i].depth) - 1.0;
+                double plane_size = ctx->width * (double)ctx->height / scale[i];
+
+                /* psnr = 10 * log10(max_value * max_value / mse) */
+                double mse = (max_value * max_value) / pow(10, pic_out.prop.f_psnr[i] / 10.0);
+
+                /* SSE = MSE * width * height / scale -> because of possible chroma downsampling */
+                sse[i] = (int64_t)floor(mse * plane_size + .5);
+            };
+
+            errors = sse;
+        }
+
+        ff_side_data_set_encoder_stats(pkt, (pic_out.i_qpplus1 - 1) * FF_QP2LAMBDA,
+                                       errors, error_count, pict_type);
+
         if (wallclock)
             ff_side_data_set_prft(pkt, wallclock);
     }
--
2.34.1


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