aacenc: add a faster version of twoloop as the "fast" coder

Does nothing fancy but still sounds very decent at 128kbps.
Still room to improve by bringing in the low pass and PNS management
from the main big twoloop which should improve its quality but not
sacrifice that much speed.
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

libavcodec/aaccoder.c

@@ -396,34 +396,148 @@ static void search_for_quantizers_fast(AVCodecContext *avctx, AACEncContext *s,
                                        SingleChannelElement *sce,
                                        const float lambda)
 {
-    int i, w, w2, g;
-    int minq = 255;
-
-    memset(sce->sf_idx, 0, sizeof(sce->sf_idx));
+    int start = 0, i, w, w2, g;
+    int destbits = avctx->bit_rate * 1024.0 / avctx->sample_rate / avctx->channels * (lambda / 120.f);
+    float dists[128] = { 0 }, uplims[128] = { 0 };
+    float maxvals[128];
+    int fflag, minscaler;
+    int its  = 0;
+    int allz = 0;
+    float minthr = INFINITY;
+
+    // for values above this the decoder might end up in an endless loop
+    // due to always having more bits than what can be encoded.
+    destbits = FFMIN(destbits, 5800);
+    //XXX: some heuristic to determine initial quantizers will reduce search time
+    //determine zero bands and upper limits
     for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
-        for (g = 0; g < sce->ics.num_swb; g++) {
+        start = 0;
+        for (g = 0;  g < sce->ics.num_swb; g++) {
+            int nz = 0;
+            float uplim = 0.0f, energy = 0.0f;
             for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                 FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[(w+w2)*16+g];
-                if (band->energy <= band->threshold) {
-                    sce->sf_idx[(w+w2)*16+g] = 218;
+                uplim += band->threshold;
+                energy += band->energy;
+                if (band->energy <= band->threshold || band->threshold == 0.0f) {
                     sce->zeroes[(w+w2)*16+g] = 1;
-                } else {
-                    sce->sf_idx[(w+w2)*16+g] = av_clip(SCALE_ONE_POS - SCALE_DIV_512 + log2f(band->threshold), 80, 218);
-                    sce->zeroes[(w+w2)*16+g] = 0;
+                    continue;
                 }
-                minq = FFMIN(minq, sce->sf_idx[(w+w2)*16+g]);
+                nz = 1;
             }
+            uplims[w*16+g] = uplim *512;
+            sce->band_type[w*16+g] = 0;
+            sce->zeroes[w*16+g] = !nz;
+            if (nz)
+                minthr = FFMIN(minthr, uplim);
+            allz |= nz;
+            start += sce->ics.swb_sizes[g];
         }
     }
-    for (i = 0; i < 128; i++) {
-        sce->sf_idx[i] = 140;
-        //av_clip(sce->sf_idx[i], minq, minq + SCALE_MAX_DIFF - 1);
+    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
+        for (g = 0;  g < sce->ics.num_swb; g++) {
+            if (sce->zeroes[w*16+g]) {
+                sce->sf_idx[w*16+g] = SCALE_ONE_POS;
+                continue;
+            }
+            sce->sf_idx[w*16+g] = SCALE_ONE_POS + FFMIN(log2f(uplims[w*16+g]/minthr)*4,59);
+        }
     }
-    //set the same quantizers inside window groups
-    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w])
-        for (g = 0;  g < sce->ics.num_swb; g++)
-            for (w2 = 1; w2 < sce->ics.group_len[w]; w2++)
-                sce->sf_idx[(w+w2)*16+g] = sce->sf_idx[w*16+g];
+
+    if (!allz)
+        return;
+    abs_pow34_v(s->scoefs, sce->coeffs, 1024);
+    ff_quantize_band_cost_cache_init(s);
+
+    for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
+        start = w*128;
+        for (g = 0;  g < sce->ics.num_swb; g++) {
+            const float *scaled = s->scoefs + start;
+            maxvals[w*16+g] = find_max_val(sce->ics.group_len[w], sce->ics.swb_sizes[g], scaled);
+            start += sce->ics.swb_sizes[g];
+        }
+    }
+
+    //perform two-loop search
+    //outer loop - improve quality
+    do {
+        int tbits, qstep;
+        minscaler = sce->sf_idx[0];
+        //inner loop - quantize spectrum to fit into given number of bits
+        qstep = its ? 1 : 32;
+        do {
+            int prev = -1;
+            tbits = 0;
+            for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
+                start = w*128;
+                for (g = 0;  g < sce->ics.num_swb; g++) {
+                    const float *coefs = sce->coeffs + start;
+                    const float *scaled = s->scoefs + start;
+                    int bits = 0;
+                    int cb;
+                    float dist = 0.0f;
+
+                    if (sce->zeroes[w*16+g] || sce->sf_idx[w*16+g] >= 218) {
+                        start += sce->ics.swb_sizes[g];
+                        continue;
+                    }
+                    minscaler = FFMIN(minscaler, sce->sf_idx[w*16+g]);
+                    cb = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
+                    for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
+                        int b;
+                        dist += quantize_band_cost_cached(s, w + w2, g,
+                                                          coefs + w2*128,
+                                                          scaled + w2*128,
+                                                          sce->ics.swb_sizes[g],
+                                                          sce->sf_idx[w*16+g],
+                                                          cb, 1.0f, INFINITY,
+                                                          &b, NULL, 0);
+                        bits += b;
+                    }
+                    dists[w*16+g] = dist - bits;
+                    if (prev != -1) {
+                        bits += ff_aac_scalefactor_bits[sce->sf_idx[w*16+g] - prev + SCALE_DIFF_ZERO];
+                    }
+                    tbits += bits;
+                    start += sce->ics.swb_sizes[g];
+                    prev = sce->sf_idx[w*16+g];
+                }
+            }
+            if (tbits > destbits) {
+                for (i = 0; i < 128; i++)
+                    if (sce->sf_idx[i] < 218 - qstep)
+                        sce->sf_idx[i] += qstep;
+            } else {
+                for (i = 0; i < 128; i++)
+                    if (sce->sf_idx[i] > 60 - qstep)
+                        sce->sf_idx[i] -= qstep;
+            }
+            qstep >>= 1;
+            if (!qstep && tbits > destbits*1.02 && sce->sf_idx[0] < 217)
+                qstep = 1;
+        } while (qstep);
+
+        fflag = 0;
+        minscaler = av_clip(minscaler, 60, 255 - SCALE_MAX_DIFF);
+
+        for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
+            for (g = 0; g < sce->ics.num_swb; g++) {
+                int prevsc = sce->sf_idx[w*16+g];
+                if (dists[w*16+g] > uplims[w*16+g] && sce->sf_idx[w*16+g] > 60) {
+                    if (find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]-1))
+                        sce->sf_idx[w*16+g]--;
+                    else //Try to make sure there is some energy in every band
+                        sce->sf_idx[w*16+g]-=2;
+                }
+                sce->sf_idx[w*16+g] = av_clip(sce->sf_idx[w*16+g], minscaler, minscaler + SCALE_MAX_DIFF);
+                sce->sf_idx[w*16+g] = FFMIN(sce->sf_idx[w*16+g], 219);
+                if (sce->sf_idx[w*16+g] != prevsc)
+                    fflag = 1;
+                sce->band_type[w*16+g] = find_min_book(maxvals[w*16+g], sce->sf_idx[w*16+g]);
+            }
+        }
+        its++;
+    } while (fflag && its < 10);
 }
 
 static void search_for_pns(AACEncContext *s, AVCodecContext *avctx, SingleChannelElement *sce)
@@ -828,7 +942,7 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
     },
     [AAC_CODER_FAST] = {
         search_for_quantizers_fast,
-        encode_window_bands_info,
+        codebook_trellis_rate,
         quantize_and_encode_band,
         ff_aac_encode_tns_info,
         ff_aac_encode_ltp_info,