[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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Hi,
please find attached a patch to propagate the SSE for a frame into the
encoder stats.
Since libx264 already provides PSNR values, this is done by basically
inverting the formula to recover the SSE values.

Would it be possible to also append other values to the errors vector?
E.g., libx264 also computes SSIM but other values could be provided.

Best,
Elias



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From dfd47efb7f7cb264fef62d0d8fb70ff8168bdfd7 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] Add the SSE calculation for libx264.

Since libx264 only provides a per-frame per-channel PSNR, this is inverted to get back the SSE.
---
 libavcodec/libx264.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
index 77a9f173b4..0fae155ff2 100644
--- a/libavcodec/libx264.c
+++ b/libavcodec/libx264.c
@@ -129,6 +129,8 @@ typedef struct X264Context {
     int roi_warned;

     int mb_info;
+
+    int64_t sse[3];
 } X264Context;

 static void X264_log(void *p, int level, const char *fmt, va_list args)
@@ -726,7 +728,40 @@ 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));
+        int error_count = 0;
+        int64_t *errors = NULL;
+
+        if (ctx->flags & AV_CODEC_FLAG_PSNR) {
+            double scale[3] = { 1,
+                (1 << pix_desc->log2_chroma_h) * (double)(1 << pix_desc->log2_chroma_w),
+                (1 << pix_desc->log2_chroma_h) * (double)(1 << pix_desc->log2_chroma_w),
+            };
+            double mse;
+            int i;
+
+            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]);
+
+            for (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 * ctx->height / scale[i];
+
+                /* psnr = -10 * log10(max_value * max_value / mse) */
+                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 */
+                x4->sse[i] = (int64_t)floor(mse * plane_size);
+            };
+
+            errors = x4->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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