AAC encoder: improve SF range utilization

This patch does 4 things, all of which interact and thus it
woudln't be possible to commit them separately without causing
either quality regressions or assertion failures.

Fate comparison targets don't all reflect improvements in
quality, yet listening tests show substantially improved quality
and stability.

1. Increase SF range utilization.

The spec requires SF delta values to be constrained within the
range -60..60. The previous code was applying that range to
the whole SF array and not only the deltas of consecutive values,
because doing so requires smarter code: zeroing or otherwise
skipping a band may invalidate lots of SF choices.

This patch implements that logic to allow the coders to utilize
the full dynamic range of scalefactors, increasing quality quite
considerably, and fixing delta-SF-related assertion failures,
since now the limitation is enforced rather than asserted.

2. PNS tweaks

The previous modification makes big improvements in twoloop's
efficiency, and every time that happens PNS logic needs to be
tweaked accordingly to avoid it from stepping all over twoloop's
decisions. This patch includes modifications of the sort.

3. Account for lowpass cutoff during PSY analysis

The closer PSY's allocation is to final allocation the better
the quality is, and given these modifications, twoloop is now
very efficient at avoiding holes. Thus, to compute accurate
thresholds, PSY needs to account for the lowpass applied
implicitly during twoloop (by zeroing high bands).

This patch makes twoloop set the cutoff in psymodel's context
the first time it runs, and makes PSY account for it during
threshold computation, making PE and threshold computations
closer to the final allocation and thus achieving better
subjective quality.

4. Tweaks to RC lambda tracking loop in relation to PNS

Without this tweak some corner cases cause quality regressions.
Basically, lambda needs to react faster to overall bitrate
efficiency changes since now PNS can be quite successful in
enforcing maximum bitrates, when PSY allocates too many bits
to the lower bands, suppressing the signals RC logic uses to
lower lambda in those cases and causing aggressive PNS.

This tweak makes PNS much less aggressive, though it can still
use some further tweaks.

Also update MIPS specializations and adjust fuzz

Also in lavc/mips/aacpsy_mips.h: remove trailing whitespace

1 files changed, 13 insertions, 7 deletions

diff --git a/libavcodec/aacpsy.c b/libavcodec/aacpsy.c
index 40b3b41..71eeb3e 100644
--- a/libavcodec/aacpsy.c
+++ b/libavcodec/aacpsy.c
@@ -305,7 +305,7 @@ static av_cold int psy_3gpp_init(FFPsyContext *ctx) {
     float prev, minscale, minath, minsnr, pe_min;
     int chan_bitrate = ctx->avctx->bit_rate / ((ctx->avctx->flags & CODEC_FLAG_QSCALE) ? 2.0f : ctx->avctx->channels);
 
-    const int bandwidth    = ctx->avctx->cutoff ? ctx->avctx->cutoff : AAC_CUTOFF(ctx->avctx);
+    const int bandwidth    = ctx->cutoff ? ctx->cutoff : AAC_CUTOFF(ctx->avctx);
     const float num_bark   = calc_bark((float)bandwidth);
 
     ctx->model_priv_data = av_mallocz(sizeof(AacPsyContext));
@@ -595,26 +595,30 @@ static float calc_reduced_thr_3gpp(AacPsyBand *band, float min_snr,
 
 #ifndef calc_thr_3gpp
 static void calc_thr_3gpp(const FFPsyWindowInfo *wi, const int num_bands, AacPsyChannel *pch,
-                          const uint8_t *band_sizes, const float *coefs)
+                          const uint8_t *band_sizes, const float *coefs, const int cutoff)
 {
     int i, w, g;
-    int start = 0;
+    int start = 0, wstart = 0;
     for (w = 0; w < wi->num_windows*16; w += 16) {
+        wstart = 0;
         for (g = 0; g < num_bands; g++) {
             AacPsyBand *band = &pch->band[w+g];
 
             float form_factor = 0.0f;
             float Temp;
             band->energy = 0.0f;
-            for (i = 0; i < band_sizes[g]; i++) {
-                band->energy += coefs[start+i] * coefs[start+i];
-                form_factor  += sqrtf(fabs(coefs[start+i]));
+            if (wstart < cutoff) {
+                for (i = 0; i < band_sizes[g]; i++) {
+                    band->energy += coefs[start+i] * coefs[start+i];
+                    form_factor  += sqrtf(fabs(coefs[start+i]));
+                }
             }
             Temp = band->energy > 0 ? sqrtf((float)band_sizes[g] / band->energy) : 0;
             band->thr      = band->energy * 0.001258925f;
             band->nz_lines = form_factor * sqrtf(Temp);
 
             start += band_sizes[g];
+            wstart += band_sizes[g];
         }
     }
 }
@@ -655,9 +659,11 @@ static void psy_3gpp_analyze_channel(FFPsyContext *ctx, int channel,
     const uint8_t *band_sizes  = ctx->bands[wi->num_windows == 8];
     AacPsyCoeffs  *coeffs      = pctx->psy_coef[wi->num_windows == 8];
     const float avoid_hole_thr = wi->num_windows == 8 ? PSY_3GPP_AH_THR_SHORT : PSY_3GPP_AH_THR_LONG;
+    const int bandwidth        = ctx->cutoff ? ctx->cutoff : AAC_CUTOFF(ctx->avctx);
+    const int cutoff           = bandwidth * 2048 / wi->num_windows / ctx->avctx->sample_rate;
 
     //calculate energies, initial thresholds and related values - 5.4.2 "Threshold Calculation"
-    calc_thr_3gpp(wi, num_bands, pch, band_sizes, coefs);
+    calc_thr_3gpp(wi, num_bands, pch, band_sizes, coefs, cutoff);
 
     //modify thresholds and energies - spread, threshold in quiet, pre-echo control
     for (w = 0; w < wi->num_windows*16; w += 16) {