[FFmpeg-devel] [PATCH] avcodec/aacenc: add high energy check to exclude unsuitable bands from PNS (PR #20521)

[Agent45 via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #20521 opened by Agent45
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20521
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20521.patch

Add a maximum energy check in mark_pns() , adapted from search_for_pns(). 
Extremely high-energy bands should be excluded early from PNS to prevent harsh artifacts.  
This resolves issue #20200.


>From b116bf897cb68a076f19304e728d957835d32b2a Mon Sep 17 00:00:00 2001
From: Agent45 <agent45@noreply.code.ffmpeg.org>
Date: Sun, 14 Sep 2025 21:03:37 +0000
Subject: [PATCH] avcodec/aacenc: add high energy check to exclude unsuitable
 bands from PNS

Add a maximum energy check in mark_pns() , adapted from search_for_pns().
Extremely high-energy bands should be excluded early from PNS to prevent harsh artifacts.
This resolves issue #20200.
---
 libavcodec/aaccoder.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index 7f1c4cdcc1..346338331d 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -636,6 +636,7 @@ static void mark_pns(AACEncContext *s, AVCodecContext *avctx, SingleChannelEleme
     int bandwidth, cutoff;
     const float lambda = s->lambda;
     const float freq_mult = avctx->sample_rate*0.5f/wlen;
+    const float thr_mult = NOISE_LAMBDA_REPLACE*(100.0f/lambda);
     const float spread_threshold = FFMIN(0.75f, NOISE_SPREAD_THRESHOLD*FFMAX(0.5f, lambda/100.f));
     const float pns_transient_energy_r = FFMIN(0.7f, lambda / 140.f);
 
@@ -690,7 +691,10 @@ static void mark_pns(AACEncContext *s, AVCodecContext *avctx, SingleChannelEleme
              * 3. on short window groups, all windows have similar energy (variations in energy would be destroyed by PNS)
              */
             sce->pns_ener[w*16+g] = sfb_energy;
-            if (sfb_energy < threshold*sqrtf(1.5f/freq_boost) || spread < spread_threshold || min_energy < pns_transient_energy_r * max_energy) {
+            if (sfb_energy < threshold*sqrtf(1.5f/freq_boost) ||
+				sfb_energy > 100.0f * threshold*thr_mult*freq_boost ||
+				spread < spread_threshold ||
+				min_energy < pns_transient_energy_r * max_energy) {
                 sce->can_pns[w*16+g] = 0;
             } else {
                 sce->can_pns[w*16+g] = 1;
-- 
2.49.1

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