mirror of
https://github.com/FFmpeg/FFmpeg.git
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262 lines
7.6 KiB
C
262 lines
7.6 KiB
C
/*
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* Common code between AC3 encoder and decoder
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* Copyright (c) 2000 Fabrice Bellard.
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file ac3.c
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* Common code between AC3 encoder and decoder.
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*/
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#include "avcodec.h"
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#include "ac3.h"
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#include "ac3tab.h"
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#include "bitstream.h"
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static inline int calc_lowcomp1(int a, int b0, int b1, int c)
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{
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if ((b0 + 256) == b1) {
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a = c;
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} else if (b0 > b1) {
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a = FFMAX(a - 64, 0);
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}
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return a;
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}
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static inline int calc_lowcomp(int a, int b0, int b1, int bin)
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{
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if (bin < 7) {
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return calc_lowcomp1(a, b0, b1, 384);
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} else if (bin < 20) {
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return calc_lowcomp1(a, b0, b1, 320);
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} else {
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return FFMAX(a - 128, 0);
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}
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}
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/* AC3 bit allocation. The algorithm is the one described in the AC3
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spec. */
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void ac3_parametric_bit_allocation(AC3BitAllocParameters *s, uint8_t *bap,
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int8_t *exp, int start, int end,
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int snroffset, int fgain, int is_lfe,
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int deltbae,int deltnseg,
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uint8_t *deltoffst, uint8_t *deltlen, uint8_t *deltba)
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{
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int bin,i,j,k,end1,v,bndstrt,bndend,lowcomp,begin;
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int fastleak,slowleak,address,tmp;
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int16_t psd[256]; /* scaled exponents */
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int16_t bndpsd[50]; /* interpolated exponents */
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int16_t excite[50]; /* excitation */
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int16_t mask[50]; /* masking value */
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/* exponent mapping to PSD */
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for(bin=start;bin<end;bin++) {
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psd[bin]=(3072 - (exp[bin] << 7));
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}
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/* PSD integration */
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j=start;
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k=masktab[start];
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do {
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v=psd[j];
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j++;
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end1 = FFMIN(bndtab[k+1], end);
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for(i=j;i<end1;i++) {
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/* logadd */
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int adr = FFMIN(FFABS(v - psd[j]) >> 1, 255);
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v = FFMAX(v, psd[j]) + latab[adr];
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j++;
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}
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bndpsd[k]=v;
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k++;
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} while (end > bndtab[k]);
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/* excitation function */
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bndstrt = masktab[start];
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bndend = masktab[end-1] + 1;
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if (bndstrt == 0) {
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lowcomp = 0;
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lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1], 384);
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excite[0] = bndpsd[0] - fgain - lowcomp;
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lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2], 384);
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excite[1] = bndpsd[1] - fgain - lowcomp;
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begin = 7;
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for (bin = 2; bin < 7; bin++) {
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if (!(is_lfe && bin == 6))
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lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1], 384);
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fastleak = bndpsd[bin] - fgain;
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slowleak = bndpsd[bin] - s->sgain;
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excite[bin] = fastleak - lowcomp;
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if (!(is_lfe && bin == 6)) {
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if (bndpsd[bin] <= bndpsd[bin+1]) {
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begin = bin + 1;
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break;
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}
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}
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}
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end1=bndend;
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if (end1 > 22) end1=22;
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for (bin = begin; bin < end1; bin++) {
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if (!(is_lfe && bin == 6))
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lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin);
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fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
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slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
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excite[bin] = FFMAX(fastleak - lowcomp, slowleak);
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}
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begin = 22;
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} else {
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/* coupling channel */
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begin = bndstrt;
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fastleak = (s->cplfleak << 8) + 768;
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slowleak = (s->cplsleak << 8) + 768;
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}
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for (bin = begin; bin < bndend; bin++) {
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fastleak = FFMAX(fastleak - s->fdecay, bndpsd[bin] - fgain);
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slowleak = FFMAX(slowleak - s->sdecay, bndpsd[bin] - s->sgain);
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excite[bin] = FFMAX(fastleak, slowleak);
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}
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/* compute masking curve */
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for (bin = bndstrt; bin < bndend; bin++) {
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tmp = s->dbknee - bndpsd[bin];
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if (tmp > 0) {
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excite[bin] += tmp >> 2;
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}
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mask[bin] = FFMAX(hth[bin >> s->halfratecod][s->fscod], excite[bin]);
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}
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/* delta bit allocation */
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if (deltbae == 0 || deltbae == 1) {
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int band, seg, delta;
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band = 0;
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for (seg = 0; seg < deltnseg; seg++) {
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band += deltoffst[seg];
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if (deltba[seg] >= 4) {
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delta = (deltba[seg] - 3) << 7;
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} else {
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delta = (deltba[seg] - 4) << 7;
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}
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for (k = 0; k < deltlen[seg]; k++) {
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mask[band] += delta;
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band++;
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}
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}
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}
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/* compute bit allocation */
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i = start;
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j = masktab[start];
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do {
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v = (FFMAX(mask[j] - snroffset - s->floor, 0) & 0x1FE0) + s->floor;
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end1 = FFMIN(bndtab[j] + bndsz[j], end);
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for (k = i; k < end1; k++) {
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address = av_clip((psd[i] - v) >> 5, 0, 63);
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bap[i] = baptab[address];
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i++;
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}
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} while (end > bndtab[j++]);
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}
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/**
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* Initializes some tables.
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* note: This function must remain thread safe because it is called by the
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* AVParser init code.
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*/
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void ac3_common_init(void)
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{
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int i, j, k, l, v;
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/* compute bndtab and masktab from bandsz */
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k = 0;
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l = 0;
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for(i=0;i<50;i++) {
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bndtab[i] = l;
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v = bndsz[i];
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for(j=0;j<v;j++) masktab[k++]=i;
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l += v;
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}
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bndtab[50] = l;
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/* generate ff_ac3_frame_sizes table */
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for(i=0; i<38; i++) {
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int br = ff_ac3_bitratetab[i >> 1];
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ff_ac3_frame_sizes[i][0] = ( 2*br );
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ff_ac3_frame_sizes[i][1] = (320*br / 147) + (i & 1);
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ff_ac3_frame_sizes[i][2] = ( 3*br );
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}
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}
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int ff_ac3_parse_header(const uint8_t buf[7], AC3HeaderInfo *hdr)
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{
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GetBitContext gbc;
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memset(hdr, 0, sizeof(*hdr));
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init_get_bits(&gbc, buf, 54);
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hdr->sync_word = get_bits(&gbc, 16);
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if(hdr->sync_word != 0x0B77)
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return -1;
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/* read ahead to bsid to make sure this is AC-3, not E-AC-3 */
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hdr->bsid = show_bits_long(&gbc, 29) & 0x1F;
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if(hdr->bsid > 10)
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return -2;
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hdr->crc1 = get_bits(&gbc, 16);
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hdr->fscod = get_bits(&gbc, 2);
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if(hdr->fscod == 3)
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return -3;
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hdr->frmsizecod = get_bits(&gbc, 6);
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if(hdr->frmsizecod > 37)
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return -4;
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skip_bits(&gbc, 5); // skip bsid, already got it
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hdr->bsmod = get_bits(&gbc, 3);
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hdr->acmod = get_bits(&gbc, 3);
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if((hdr->acmod & 1) && hdr->acmod != 1) {
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hdr->cmixlev = get_bits(&gbc, 2);
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}
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if(hdr->acmod & 4) {
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hdr->surmixlev = get_bits(&gbc, 2);
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}
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if(hdr->acmod == 2) {
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hdr->dsurmod = get_bits(&gbc, 2);
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}
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hdr->lfeon = get_bits1(&gbc);
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hdr->halfratecod = FFMAX(hdr->bsid, 8) - 8;
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hdr->sample_rate = ff_ac3_freqs[hdr->fscod] >> hdr->halfratecod;
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hdr->bit_rate = (ff_ac3_bitratetab[hdr->frmsizecod>>1] * 1000) >> hdr->halfratecod;
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hdr->channels = ff_ac3_channels[hdr->acmod] + hdr->lfeon;
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hdr->frame_size = ff_ac3_frame_sizes[hdr->frmsizecod][hdr->fscod] * 2;
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return 0;
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}
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