aaccoder: add frequency scaling and quantization correction for PNS

This commit once again improves the PNS implementation by scaling the
thresholds with frequency. The thresholds get looser as the frequency
increases since higher frequencies are basically noise to human ears.

Also, this introduces quantization error correction for PNS. Should
the error be too much, no PNS will be used. The energy_ratio is used
to regulate the actual encoded PNS energy: if the generated PNS
energy is higher than the energy from the psy system, energy_ratio
is used to correct it so that hopefully once requantized and
transmitted the value in the decoder will be closer to what the
encoder has.

Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

1 files changed, 17 insertions, 11 deletions

diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index 8a241d2c06..cf4b11b3bc 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -876,36 +876,39 @@ static void search_for_pns(AACEncContext *s, AVCodecContext *avctx, SingleChanne
         for (g = 0;  g < sce->ics.num_swb; g++) {
             int noise_sfi, try_pns = 0;
             float dist1 = 0.0f, dist2 = 0.0f, noise_amp;
-            float energy = 0.0f, threshold = 0.0f, spread = 0.0f;
+            float pns_energy = 0.0f, energy_ratio, dist_thresh;
+            float sfb_energy = 0.0f, threshold = 0.0f, spread = 0.0f;
+            float freq_boost = FFMAX(0.88f*start*freq_mult/NOISE_LOW_LIMIT, 1.0f);
             if (start*freq_mult < NOISE_LOW_LIMIT) {
                 start += sce->ics.swb_sizes[g];
                 continue;
+            } else {
+                dist_thresh = FFMIN(0.008f*(NOISE_LOW_LIMIT/start*freq_mult), 1.11f);
             }
             for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                 band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
-                energy    += band->energy;
-                spread    += band->spread;
-                threshold += band->threshold;
+                sfb_energy += band->energy;
+                spread     += band->spread;
+                threshold  += band->threshold;
             }
-            sce->pns_ener[w*16+g] = energy;
 
             if (sce->zeroes[w*16+g]) {
                 try_pns = 1;
-            } else if (energy < threshold) {
+            } else if (sfb_energy < threshold*freq_boost) {
                 try_pns = 1;
             } else if (spread > spread_threshold) {
                 try_pns = 0;
-            } else if (energy < threshold*thr_mult) {
+            } else if (sfb_energy < threshold*thr_mult*freq_boost) {
                 try_pns = 1;
             }
 
-            if (!try_pns || !energy) {
+            if (!try_pns || !sfb_energy) {
                 start += sce->ics.swb_sizes[g];
                 continue;
             }
 
-            noise_sfi = av_clip(roundf(log2f(energy)*2), -100, 155);  /* Quantize */
-            noise_amp = -ff_aac_pow2sf_tab[noise_sfi + POW_SF2_ZERO]; /* Dequantize */
+            noise_sfi = av_clip(roundf(log2f(sfb_energy)*2), -100, 155); /* Quantize */
+            noise_amp = -ff_aac_pow2sf_tab[noise_sfi + POW_SF2_ZERO];    /* Dequantize */
             for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                 float band_energy, scale;
                 band = &s->psy.ch[s->cur_channel+0].psy_bands[(w+w2)*16+g];
@@ -914,6 +917,7 @@ static void search_for_pns(AACEncContext *s, AVCodecContext *avctx, SingleChanne
                 band_energy = s->fdsp->scalarproduct_float(PNS, PNS, sce->ics.swb_sizes[g]);
                 scale = noise_amp/sqrtf(band_energy);
                 s->fdsp->vector_fmul_scalar(PNS, PNS, scale, sce->ics.swb_sizes[g]);
+                pns_energy += s->fdsp->scalarproduct_float(PNS, PNS, sce->ics.swb_sizes[g]);
                 abs_pow34_v(NOR34, &sce->coeffs[start+(w+w2)*128], sce->ics.swb_sizes[g]);
                 abs_pow34_v(PNS34, PNS, sce->ics.swb_sizes[g]);
                 dist1 += quantize_band_cost(s, &sce->coeffs[start + (w+w2)*128],
@@ -929,7 +933,9 @@ static void search_for_pns(AACEncContext *s, AVCodecContext *avctx, SingleChanne
                                             NOISE_BT,
                                             lambda/band->threshold, INFINITY, NULL, 0);
             }
-            if (dist2 < dist1) {
+            energy_ratio = sfb_energy/pns_energy; /* Compensates for quantization error */
+            sce->pns_ener[w*16+g] = energy_ratio*sfb_energy;
+            if (energy_ratio > 0.80f && energy_ratio < 1.20f && dist1/dist2 > dist_thresh) {
                 sce->band_type[w*16+g] = NOISE_BT;
                 sce->zeroes[w*16+g] = 0;
                 if (sce->band_type[w*16+g-1] != NOISE_BT && /* Prevent holes */