/* * Common code between AC3 encoder and decoder * Copyright (c) 2000 Fabrice Bellard. * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /** * @file ac3.c * Common code between AC3 encoder and decoder. */ #include "avcodec.h" #include "ac3.h" #include "bitstream.h" static uint8_t bndtab[51]; static uint8_t masktab[253]; static inline int calc_lowcomp1(int a, int b0, int b1, int c) { if ((b0 + 256) == b1) { a = c; } else if (b0 > b1) { a = FFMAX(a - 64, 0); } return a; } static inline int calc_lowcomp(int a, int b0, int b1, int bin) { if (bin < 7) { return calc_lowcomp1(a, b0, b1, 384); } else if (bin < 20) { return calc_lowcomp1(a, b0, b1, 320); } else { return FFMAX(a - 128, 0); } } void ff_ac3_bit_alloc_calc_psd(int8_t *exp, int start, int end, int16_t *psd, int16_t *bndpsd) { int bin, i, j, k, end1, v; /* exponent mapping to PSD */ for(bin=start;bin<end;bin++) { psd[bin]=(3072 - (exp[bin] << 7)); } /* PSD integration */ j=start; k=masktab[start]; do { v=psd[j]; j++; end1 = FFMIN(bndtab[k+1], end); for(i=j;i<end1;i++) { /* logadd */ int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255); v = FFMAX(v, psd[j]) + ff_ac3_latab[adr]; j++; } bndpsd[k]=v; k++; } while (end > bndtab[k]); } void ff_ac3_bit_alloc_calc_mask(AC3BitAllocParameters *s, int16_t *bndpsd, int start, int end, int fgain, int is_lfe, int deltbae, int deltnseg, uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba, int16_t *mask) { int16_t excite[50]; /* excitation */ int bin, k; int bndstrt, bndend, begin, end1, tmp; int lowcomp, fastleak, slowleak; /* excitation function */ bndstrt = masktab[start]; bndend = masktab[end-1] + 1; if (bndstrt == 0) { lowcomp = 0; lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1], 384); excite[0] = bndpsd[0] - fgain - lowcomp; lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2], 384); excite[1] = bndpsd[1] - fgain - lowcomp; begin = 7; for (bin = 2; bin < 7; bin++) { if (!(is_lfe && bin == 6)) lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1], 384); fastleak = bndpsd[bin] - fgain; slowleak = bndpsd[bin] - s->sgain; excite[bin] = fastleak - lowcomp; if (!(is_lfe && bin == 6)) { if (bndpsd[bin] <= bndpsd[bin+1]) { begin = bin + 1; break; } } } end1=bndend; if (end1 > 22) end1=22; for (bin = begin; bin < end1; bin++) { if (!(is_lfe && bin == 6)) lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin); fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain); slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain); excite[bin] = FFMAX(fastleak - lowcomp, slowleak); } begin = 22; } else { /* coupling channel */ begin = bndstrt; fastleak = (s->cplfleak << 8) + 768; slowleak = (s->cplsleak << 8) + 768; } for (bin = begin; bin < bndend; bin++) { fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain); slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain); excite[bin] = FFMAX(fastleak, slowleak); } /* compute masking curve */ for (bin = bndstrt; bin < bndend; bin++) { tmp = s->dbknee - bndpsd[bin]; if (tmp > 0) { excite[bin] += tmp >> 2; } mask[bin] = FFMAX(ff_ac3_hth[bin >> s->halfratecod][s->fscod], excite[bin]); } /* delta bit allocation */ if (deltbae == DBA_REUSE || deltbae == DBA_NEW) { int band, seg, delta; band = 0; for (seg = 0; seg < deltnseg; seg++) { band += deltoffst[seg]; if (deltba[seg] >= 4) { delta = (deltba[seg] - 3) << 7; } else { delta = (deltba[seg] - 4) << 7; } for (k = 0; k < deltlen[seg]; k++) { mask[band] += delta; band++; } } } } void ff_ac3_bit_alloc_calc_bap(int16_t *mask, int16_t *psd, int start, int end, int snroffset, int floor, uint8_t *bap) { int i, j, k, end1, v, address; /* special case, if snroffset is -960, set all bap's to zero */ if(snroffset == -960) { memset(bap, 0, 256); return; } i = start; j = masktab[start]; do { v = (FFMAX(mask[j] - snroffset - floor, 0) & 0x1FE0) + floor; end1 = FFMIN(bndtab[j] + ff_ac3_bndsz[j], end); for (k = i; k < end1; k++) { address = av_clip((psd[i] - v) >> 5, 0, 63); bap[i] = ff_ac3_baptab[address]; i++; } } while (end > bndtab[j++]); } /* AC3 bit allocation. The algorithm is the one described in the AC3 spec. */ void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap, int8_t *exp, int start, int end, int snroffset, int fgain, int is_lfe, int deltbae,int deltnseg, uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba) { int16_t psd[256]; /* scaled exponents */ int16_t bndpsd[50]; /* interpolated exponents */ int16_t mask[50]; /* masking value */ ff_ac3_bit_alloc_calc_psd(exp, start, end, psd, bndpsd); ff_ac3_bit_alloc_calc_mask(s, bndpsd, start, end, fgain, is_lfe, deltbae, deltnseg, deltoffst, deltlen, deltba, mask); ff_ac3_bit_alloc_calc_bap(mask, psd, start, end, snroffset, s->floor, bap); } /** * Initializes some tables. * note: This function must remain thread safe because it is called by the * AVParser init code. */ void ac3_common_init(void) { int i, j, k, l, v; /* compute bndtab and masktab from bandsz */ k = 0; l = 0; for(i=0;i<50;i++) { bndtab[i] = l; v = ff_ac3_bndsz[i]; for(j=0;j<v;j++) masktab[k++]=i; l += v; } bndtab[50] = l; }