aaccoder.c

                    if (sce->ics.num_windows == 1 && maxval < t) {
                        maxval  = t;
                        peakpos = start+i;
                    }
                }
            }
            if (sce->ics.num_windows == 1) {
                start2 = FFMAX(peakpos - 2, start2);
                end2   = FFMIN(peakpos + 3, end2);
            } else {
                start2 -= start;
                end2   -= start;
            }
            start += size;
            thr = pow(thr / (avg_energy * (end2 - start2)), 0.3 + 0.1*(lastband - g) / lastband);
            t   = 1.0 - (1.0 * start2 / last);
            uplim[w*16+g] = distfact / (1.4 * thr + t*t*t + 0.075);
        }
    }
    memset(sce->sf_idx, 0, sizeof(sce->sf_idx));
    abs_pow34_v(s->scoefs, sce->coeffs, 1024);
    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;
            const int size      = sce->ics.swb_sizes[g];
            int scf, prev_scf, step;
            int min_scf = -1, max_scf = 256;
            float curdiff;
            if (maxq[w*16+g] < 21.544) {
                sce->zeroes[w*16+g] = 1;
                start += size;
                continue;
            }
            sce->zeroes[w*16+g] = 0;
            scf  = prev_scf = av_clip(SCALE_ONE_POS - SCALE_DIV_512 - log2f(1/maxq[w*16+g])*16/3, 60, 218);
            for (;;) {
                float dist = 0.0f;
                int quant_max;

                for (w2 = 0; w2 < sce->ics.group_len[w]; w2++) {
                    int b;
                    dist += quantize_band_cost(s, coefs + w2*128,
                                               scaled + w2*128,
                                               sce->ics.swb_sizes[g],
                                               scf,
                                               ESC_BT,
                                               lambda,
                                               INFINITY,
                                               &b);
                    dist -= b;
                }
                dist *= 1.0f / 512.0f / lambda;
                quant_max = quant(maxq[w*16+g], ff_aac_pow2sf_tab[POW_SF2_ZERO - scf + SCALE_ONE_POS - SCALE_DIV_512]);
                if (quant_max >= 8191) { // too much, return to the previous quantizer
                    sce->sf_idx[w*16+g] = prev_scf;
                    break;
                }
                prev_scf = scf;
                curdiff = fabsf(dist - uplim[w*16+g]);
                if (curdiff <= 1.0f)
                    step = 0;
                else
                    step = log2f(curdiff);
                if (dist > uplim[w*16+g])
                    step = -step;
                scf += step;
                scf = av_clip_uint8(scf);
                step = scf - prev_scf;
                if (FFABS(step) <= 1 || (step > 0 && scf >= max_scf) || (step < 0 && scf <= min_scf)) {
                    sce->sf_idx[w*16+g] = av_clip(scf, min_scf, max_scf);
                    break;
                }
                if (step > 0)
                    min_scf = prev_scf;
                else
                    max_scf = prev_scf;
            }
            start += size;
        }
    }
    minq = sce->sf_idx[0] ? sce->sf_idx[0] : INT_MAX;
    for (i = 1; i < 128; i++) {
        if (!sce->sf_idx[i])
            sce->sf_idx[i] = sce->sf_idx[i-1];
        else
            minq = FFMIN(minq, sce->sf_idx[i]);
    }
    if (minq == INT_MAX)
        minq = 0;
    minq = FFMIN(minq, SCALE_MAX_POS);
    maxsf = FFMIN(minq + SCALE_MAX_DIFF, SCALE_MAX_POS);
    for (i = 126; i >= 0; i--) {
        if (!sce->sf_idx[i])
            sce->sf_idx[i] = sce->sf_idx[i+1];
        sce->sf_idx[i] = av_clip(sce->sf_idx[i], minq, maxsf);
    }
}

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));
    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 = 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;
                    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;
                }
                minq = FFMIN(minq, sce->sf_idx[(w+w2)*16+g]);
            }
        }
    }
    for (i = 0; i < 128; i++) {
        sce->sf_idx[i] = 140;
        //av_clip(sce->sf_idx[i], minq, minq + SCALE_MAX_DIFF - 1);
    }
    //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];
}

static void search_for_ms(AACEncContext *s, ChannelElement *cpe,
                          const float lambda)
{
    int start = 0, i, w, w2, g;
    float M[128], S[128];
    float *L34 = s->scoefs, *R34 = s->scoefs + 128, *M34 = s->scoefs + 128*2, *S34 = s->scoefs + 128*3;
    SingleChannelElement *sce0 = &cpe->ch[0];
    SingleChannelElement *sce1 = &cpe->ch[1];
    if (!cpe->common_window)
        return;
    for (w = 0; w < sce0->ics.num_windows; w += sce0->ics.group_len[w]) {
        start = 0;
        for (g = 0;  g < sce0->ics.num_swb; g++) {
            if (!cpe->ch[0].zeroes[w*16+g] && !cpe->ch[1].zeroes[w*16+g]) {
                float dist1 = 0.0f, dist2 = 0.0f;
                for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
                    FFPsyBand *band0 = &s->psy.ch[s->cur_channel+0].psy_bands[(w+w2)*16+g];
                    FFPsyBand *band1 = &s->psy.ch[s->cur_channel+1].psy_bands[(w+w2)*16+g];
                    float minthr = FFMIN(band0->threshold, band1->threshold);
                    float maxthr = FFMAX(band0->threshold, band1->threshold);
                    for (i = 0; i < sce0->ics.swb_sizes[g]; i++) {
                        M[i] = (sce0->pcoeffs[start+(w+w2)*128+i]
                              + sce1->pcoeffs[start+(w+w2)*128+i]) * 0.5;
                        S[i] =  M[i]
                              - sce1->pcoeffs[start+(w+w2)*128+i];
                    }
                    abs_pow34_v(L34, sce0->coeffs+start+(w+w2)*128, sce0->ics.swb_sizes[g]);
                    abs_pow34_v(R34, sce1->coeffs+start+(w+w2)*128, sce0->ics.swb_sizes[g]);
                    abs_pow34_v(M34, M,                         sce0->ics.swb_sizes[g]);
                    abs_pow34_v(S34, S,                         sce0->ics.swb_sizes[g]);
                    dist1 += quantize_band_cost(s, sce0->coeffs + start + (w+w2)*128,
                                                L34,
                                                sce0->ics.swb_sizes[g],
                                                sce0->sf_idx[(w+w2)*16+g],
                                                sce0->band_type[(w+w2)*16+g],
                                                lambda / band0->threshold, INFINITY, NULL);
                    dist1 += quantize_band_cost(s, sce1->coeffs + start + (w+w2)*128,
                                                R34,
                                                sce1->ics.swb_sizes[g],
                                                sce1->sf_idx[(w+w2)*16+g],
                                                sce1->band_type[(w+w2)*16+g],
                                                lambda / band1->threshold, INFINITY, NULL);
                    dist2 += quantize_band_cost(s, M,
                                                M34,
                                                sce0->ics.swb_sizes[g],
                                                sce0->sf_idx[(w+w2)*16+g],
                                                sce0->band_type[(w+w2)*16+g],
                                                lambda / maxthr, INFINITY, NULL);
                    dist2 += quantize_band_cost(s, S,
                                                S34,
                                                sce1->ics.swb_sizes[g],
                                                sce1->sf_idx[(w+w2)*16+g],
                                                sce1->band_type[(w+w2)*16+g],
                                                lambda / minthr, INFINITY, NULL);
                }
                cpe->ms_mask[w*16+g] = dist2 < dist1;
            }
            start += sce0->ics.swb_sizes[g];
        }
    }
}

AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
    [AAC_CODER_FAAC] = {
        search_for_quantizers_faac,
        encode_window_bands_info,
        quantize_and_encode_band,
        set_special_band_scalefactors,
        search_for_ms,
    },
    [AAC_CODER_ANMR] = {
        search_for_quantizers_anmr,
        encode_window_bands_info,
        quantize_and_encode_band,
        set_special_band_scalefactors,
        search_for_ms,
    },
    [AAC_CODER_TWOLOOP] = {
        search_for_quantizers_twoloop,
        codebook_trellis_rate,
        quantize_and_encode_band,
        set_special_band_scalefactors,
        search_for_ms,
    },
    [AAC_CODER_FAST] = {
        search_for_quantizers_fast,
        encode_window_bands_info,
        quantize_and_encode_band,
        set_special_band_scalefactors,
        search_for_ms,
    },
};