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FFmpeg/libavcodec/ac3enc.c
Fabrice Bellard de6d9b6404 Initial revision 
Originally committed as revision 5 to svn://svn.ffmpeg.org/ffmpeg/trunk
2001-07-22 14:18:56 +00:00

1461 lines
39 KiB
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/*
* The simplest AC3 encoder
* Copyright (c) 2000 Gerard Lantau.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include "avcodec.h"
#include "ac3enc.h"
#include "ac3tab.h"
//#define DEBUG
//#define DEBUG_BITALLOC
#define NDEBUG
#include <assert.h>
#define MDCT_NBITS 9
#define N (1 << MDCT_NBITS)
#define NB_BLOCKS 6 /* number of PCM blocks inside an AC3 frame */
/* new exponents are sent if their Norm 1 exceed this number */
#define EXP_DIFF_THRESHOLD 1000
/* exponent encoding strategy */
#define EXP_REUSE 0
#define EXP_NEW 1
#define EXP_D15 1
#define EXP_D25 2
#define EXP_D45 3
static void fft_init(int ln);
static void ac3_crc_init(void);
static inline INT16 fix15(float a)
{
int v;
v = (int)(a * (float)(1 << 15));
if (v < -32767)
v = -32767;
else if (v > 32767)
v = 32767;
return v;
}
static inline int calc_lowcomp1(int a, int b0, int b1)
{
if ((b0 + 256) == b1) {
a = 384 ;
} else if (b0 > b1) {
a = a - 64;
if (a < 0) a=0;
}
return a;
}
static inline int calc_lowcomp(int a, int b0, int b1, int bin)
{
if (bin < 7) {
if ((b0 + 256) == b1) {
a = 384 ;
} else if (b0 > b1) {
a = a - 64;
if (a < 0) a=0;
}
} else if (bin < 20) {
if ((b0 + 256) == b1) {
a = 320 ;
} else if (b0 > b1) {
a= a - 64;
if (a < 0) a=0;
}
} else {
a = a - 128;
if (a < 0) a=0;
}
return a;
}
/* AC3 bit allocation. The algorithm is the one described in the AC3
spec with some optimizations because of our simplified encoding
assumptions. */
void parametric_bit_allocation(AC3EncodeContext *s, UINT8 *bap,
INT8 *exp, int start, int end,
int snroffset, int fgain)
{
int bin,i,j,k,end1,v,v1,bndstrt,bndend,lowcomp,begin;
int fastleak,slowleak,address,tmp;
INT16 psd[256]; /* scaled exponents */
INT16 bndpsd[50]; /* interpolated exponents */
INT16 excite[50]; /* excitation */
INT16 mask[50]; /* masking value */
/* 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=bndtab[k+1];
if (end1 > end) end1=end;
for(i=j;i<end1;i++) {
int c,adr;
/* logadd */
v1=psd[j];
c=v-v1;
if (c >= 0) {
adr=c >> 1;
if (adr > 255) adr=255;
v=v + latab[adr];
} else {
adr=(-c) >> 1;
if (adr > 255) adr=255;
v=v1 + latab[adr];
}
j++;
}
bndpsd[k]=v;
k++;
} while (end > bndtab[k]);
/* excitation function */
bndstrt = masktab[start];
bndend = masktab[end-1] + 1;
lowcomp = 0;
lowcomp = calc_lowcomp1(lowcomp, bndpsd[0], bndpsd[1]) ;
excite[0] = bndpsd[0] - fgain - lowcomp ;
lowcomp = calc_lowcomp1(lowcomp, bndpsd[1], bndpsd[2]) ;
excite[1] = bndpsd[1] - fgain - lowcomp ;
begin = 7 ;
for (bin = 2; bin < 7; bin++) {
lowcomp = calc_lowcomp1(lowcomp, bndpsd[bin], bndpsd[bin+1]) ;
fastleak = bndpsd[bin] - fgain ;
slowleak = bndpsd[bin] - s->sgain ;
excite[bin] = fastleak - lowcomp ;
if (bndpsd[bin] <= bndpsd[bin+1]) {
begin = bin + 1 ;
break ;
}
}
end1=bndend;
if (end1 > 22) end1=22;
for (bin = begin; bin < end1; bin++) {
lowcomp = calc_lowcomp(lowcomp, bndpsd[bin], bndpsd[bin+1], bin) ;
fastleak -= s->fdecay ;
v = bndpsd[bin] - fgain;
if (fastleak < v) fastleak = v;
slowleak -= s->sdecay ;
v = bndpsd[bin] - s->sgain;
if (slowleak < v) slowleak = v;
v=fastleak - lowcomp;
if (slowleak > v) v=slowleak;
excite[bin] = v;
}
for (bin = 22; bin < bndend; bin++) {
fastleak -= s->fdecay ;
v = bndpsd[bin] - fgain;
if (fastleak < v) fastleak = v;
slowleak -= s->sdecay ;
v = bndpsd[bin] - s->sgain;
if (slowleak < v) slowleak = v;
v=fastleak;
if (slowleak > v) v = slowleak;
excite[bin] = v;
}
/* compute masking curve */
for (bin = bndstrt; bin < bndend; bin++) {
v1 = excite[bin];
tmp = s->dbknee - bndpsd[bin];
if (tmp > 0) {
v1 += tmp >> 2;
}
v=hth[bin >> s->halfratecod][s->fscod];
if (v1 > v) v=v1;
mask[bin] = v;
}
/* compute bit allocation */
i = start ;
j = masktab[start] ;
do {
v=mask[j];
v -= snroffset ;
v -= s->floor ;
if (v < 0) v = 0;
v &= 0x1fe0 ;
v += s->floor ;
end1=bndtab[j] + bndsz[j];
if (end1 > end) end1=end;
for (k = i; k < end1; k++) {
address = (psd[i] - v) >> 5 ;
if (address < 0) address=0;
else if (address > 63) address=63;
bap[i] = baptab[address];
i++;
}
} while (end > bndtab[j++]) ;
}
typedef struct IComplex {
short re,im;
} IComplex;
static void fft_init(int ln)
{
int i, j, m, n;
float alpha;
n = 1 << ln;
for(i=0;i<(n/2);i++) {
alpha = 2 * M_PI * (float)i / (float)n;
costab[i] = fix15(cos(alpha));
sintab[i] = fix15(sin(alpha));
}
for(i=0;i<n;i++) {
m=0;
for(j=0;j<ln;j++) {
m |= ((i >> j) & 1) << (ln-j-1);
}
fft_rev[i]=m;
}
}
/* butter fly op */
#define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1) \
{\
int ax, ay, bx, by;\
bx=pre1;\
by=pim1;\
ax=qre1;\
ay=qim1;\
pre = (bx + ax) >> 1;\
pim = (by + ay) >> 1;\
qre = (bx - ax) >> 1;\
qim = (by - ay) >> 1;\
}
#define MUL16(a,b) ((a) * (b))
#define CMUL(pre, pim, are, aim, bre, bim) \
{\
pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15;\
pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15;\
}
/* do a 2^n point complex fft on 2^ln points. */
static void fft(IComplex *z, int ln)
{
int j, l, np, np2;
int nblocks, nloops;
register IComplex *p,*q;
int tmp_re, tmp_im;
np = 1 << ln;
/* reverse */
for(j=0;j<np;j++) {
int k;
IComplex tmp;
k = fft_rev[j];
if (k < j) {
tmp = z[k];
z[k] = z[j];
z[j] = tmp;
}
}
/* pass 0 */
p=&z[0];
j=(np >> 1);
do {
BF(p[0].re, p[0].im, p[1].re, p[1].im,
p[0].re, p[0].im, p[1].re, p[1].im);
p+=2;
} while (--j != 0);
/* pass 1 */
p=&z[0];
j=np >> 2;
do {
BF(p[0].re, p[0].im, p[2].re, p[2].im,
p[0].re, p[0].im, p[2].re, p[2].im);
BF(p[1].re, p[1].im, p[3].re, p[3].im,
p[1].re, p[1].im, p[3].im, -p[3].re);
p+=4;
} while (--j != 0);
/* pass 2 .. ln-1 */
nblocks = np >> 3;
nloops = 1 << 2;
np2 = np >> 1;
do {
p = z;
q = z + nloops;
for (j = 0; j < nblocks; ++j) {
BF(p->re, p->im, q->re, q->im,
p->re, p->im, q->re, q->im);
p++;
q++;
for(l = nblocks; l < np2; l += nblocks) {
CMUL(tmp_re, tmp_im, costab[l], -sintab[l], q->re, q->im);
BF(p->re, p->im, q->re, q->im,
p->re, p->im, tmp_re, tmp_im);
p++;
q++;
}
p += nloops;
q += nloops;
}
nblocks = nblocks >> 1;
nloops = nloops << 1;
} while (nblocks != 0);
}
/* do a 512 point mdct */
static void mdct512(INT32 *out, INT16 *in)
{
int i, re, im, re1, im1;
INT16 rot[N];
IComplex x[N/4];
/* shift to simplify computations */
for(i=0;i<N/4;i++)
rot[i] = -in[i + 3*N/4];
for(i=N/4;i<N;i++)
rot[i] = in[i - N/4];
/* pre rotation */
for(i=0;i<N/4;i++) {
re = ((int)rot[2*i] - (int)rot[N-1-2*i]) >> 1;
im = -((int)rot[N/2+2*i] - (int)rot[N/2-1-2*i]) >> 1;
CMUL(x[i].re, x[i].im, re, im, -xcos1[i], xsin1[i]);
}
fft(x, MDCT_NBITS - 2);
/* post rotation */
for(i=0;i<N/4;i++) {
re = x[i].re;
im = x[i].im;
CMUL(re1, im1, re, im, xsin1[i], xcos1[i]);
out[2*i] = im1;
out[N/2-1-2*i] = re1;
}
}
/* XXX: use another norm ? */
static int calc_exp_diff(UINT8 *exp1, UINT8 *exp2, int n)
{
int sum, i;
sum = 0;
for(i=0;i<n;i++) {
sum += abs(exp1[i] - exp2[i]);
}
return sum;
}
static void compute_exp_strategy(UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
UINT8 exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
int ch)
{
int i, j;
int exp_diff;
/* estimate if the exponent variation & decide if they should be
reused in the next frame */
exp_strategy[0][ch] = EXP_NEW;
for(i=1;i<NB_BLOCKS;i++) {
exp_diff = calc_exp_diff(exp[i][ch], exp[i-1][ch], N/2);
#ifdef DEBUG
printf("exp_diff=%d\n", exp_diff);
#endif
if (exp_diff > EXP_DIFF_THRESHOLD)
exp_strategy[i][ch] = EXP_NEW;
else
exp_strategy[i][ch] = EXP_REUSE;
}
/* now select the encoding strategy type : if exponents are often
recoded, we use a coarse encoding */
i = 0;
while (i < NB_BLOCKS) {
j = i + 1;
while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE)
j++;
switch(j - i) {
case 1:
exp_strategy[i][ch] = EXP_D45;
break;
case 2:
case 3:
exp_strategy[i][ch] = EXP_D25;
break;
default:
exp_strategy[i][ch] = EXP_D15;
break;
}
i = j;
}
}
/* set exp[i] to min(exp[i], exp1[i]) */
static void exponent_min(UINT8 exp[N/2], UINT8 exp1[N/2], int n)
{
int i;
for(i=0;i<n;i++) {
if (exp1[i] < exp[i])
exp[i] = exp1[i];
}
}
/* update the exponents so that they are the ones the decoder will
decode. Return the number of bits used to code the exponents */
static int encode_exp(UINT8 encoded_exp[N/2],
UINT8 exp[N/2],
int nb_exps,
int exp_strategy)
{
int group_size, nb_groups, i, j, k, recurse, exp_min, delta;
UINT8 exp1[N/2];
switch(exp_strategy) {
case EXP_D15:
group_size = 1;
break;
case EXP_D25:
group_size = 2;
break;
default:
case EXP_D45:
group_size = 4;
break;
}
nb_groups = ((nb_exps + (group_size * 3) - 4) / (3 * group_size)) * 3;
/* for each group, compute the minimum exponent */
exp1[0] = exp[0]; /* DC exponent is handled separately */
k = 1;
for(i=1;i<=nb_groups;i++) {
exp_min = exp[k];
assert(exp_min >= 0 && exp_min <= 24);
for(j=1;j<group_size;j++) {
if (exp[k+j] < exp_min)
exp_min = exp[k+j];
}
exp1[i] = exp_min;
k += group_size;
}
/* constraint for DC exponent */
if (exp1[0] > 15)
exp1[0] = 15;
/* Iterate until the delta constraints between each groups are
satisfyed. I'm sure it is possible to find a better algorithm,
but I am lazy */
do {
recurse = 0;
for(i=1;i<=nb_groups;i++) {
delta = exp1[i] - exp1[i-1];
if (delta > 2) {
/* if delta too big, we encode a smaller exponent */
exp1[i] = exp1[i-1] + 2;
} else if (delta < -2) {
/* if delta is too small, we must decrease the previous
exponent, which means we must recurse */
recurse = 1;
exp1[i-1] = exp1[i] + 2;
}
}
} while (recurse);
/* now we have the exponent values the decoder will see */
encoded_exp[0] = exp1[0];
k = 1;
for(i=1;i<=nb_groups;i++) {
for(j=0;j<group_size;j++) {
encoded_exp[k+j] = exp1[i];
}
k += group_size;
}
#if defined(DEBUG)
printf("exponents: strategy=%d\n", exp_strategy);
for(i=0;i<=nb_groups * group_size;i++) {
printf("%d ", encoded_exp[i]);
}
printf("\n");
#endif
return 4 + (nb_groups / 3) * 7;
}
/* return the size in bits taken by the mantissa */
int compute_mantissa_size(AC3EncodeContext *s, UINT8 *m, int nb_coefs)
{
int bits, mant, i;
bits = 0;
for(i=0;i<nb_coefs;i++) {
mant = m[i];
switch(mant) {
case 0:
/* nothing */
break;
case 1:
/* 3 mantissa in 5 bits */
if (s->mant1_cnt == 0)
bits += 5;
if (++s->mant1_cnt == 3)
s->mant1_cnt = 0;
break;
case 2:
/* 3 mantissa in 7 bits */
if (s->mant2_cnt == 0)
bits += 7;
if (++s->mant2_cnt == 3)
s->mant2_cnt = 0;
break;
case 3:
bits += 3;
break;
case 4:
/* 2 mantissa in 7 bits */
if (s->mant4_cnt == 0)
bits += 7;
if (++s->mant4_cnt == 2)
s->mant4_cnt = 0;
break;
case 14:
bits += 14;
break;
case 15:
bits += 16;
break;
default:
bits += mant - 1;
break;
}
}
return bits;
}
static int bit_alloc(AC3EncodeContext *s,
UINT8 bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
UINT8 encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
int frame_bits, int csnroffst, int fsnroffst)
{
int i, ch;
/* compute size */
for(i=0;i<NB_BLOCKS;i++) {
s->mant1_cnt = 0;
s->mant2_cnt = 0;
s->mant4_cnt = 0;
for(ch=0;ch<s->nb_channels;ch++) {
parametric_bit_allocation(s, bap[i][ch], encoded_exp[i][ch],
0, s->nb_coefs[ch],
(((csnroffst-15) << 4) +
fsnroffst) << 2,
fgaintab[s->fgaincod[ch]]);
frame_bits += compute_mantissa_size(s, bap[i][ch],
s->nb_coefs[ch]);
}
}
#if 0
printf("csnr=%d fsnr=%d frame_bits=%d diff=%d\n",
csnroffst, fsnroffst, frame_bits,
16 * s->frame_size - ((frame_bits + 7) & ~7));
#endif
return 16 * s->frame_size - frame_bits;
}
#define SNR_INC1 4
static int compute_bit_allocation(AC3EncodeContext *s,
UINT8 bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
UINT8 encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
int frame_bits)
{
int i, ch;
int csnroffst, fsnroffst;
UINT8 bap1[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
/* init default parameters */
s->sdecaycod = 2;
s->fdecaycod = 1;
s->sgaincod = 1;
s->dbkneecod = 2;
s->floorcod = 4;
for(ch=0;ch<s->nb_channels;ch++)
s->fgaincod[ch] = 4;
/* compute real values */
s->sdecay = sdecaytab[s->sdecaycod] >> s->halfratecod;
s->fdecay = fdecaytab[s->fdecaycod] >> s->halfratecod;
s->sgain = sgaintab[s->sgaincod];
s->dbknee = dbkneetab[s->dbkneecod];
s->floor = floortab[s->floorcod];
/* header size */
frame_bits += 65;
if (s->acmod == 2)
frame_bits += 2;
/* audio blocks */
for(i=0;i<NB_BLOCKS;i++) {
frame_bits += s->nb_channels * 2 + 2;
if (s->acmod == 2)
frame_bits++;
frame_bits += 2 * s->nb_channels;
for(ch=0;ch<s->nb_channels;ch++) {
if (exp_strategy[i][ch] != EXP_REUSE)
frame_bits += 6 + 2;
}
frame_bits++; /* baie */
frame_bits++; /* snr */
frame_bits += 2; /* delta / skip */
}
frame_bits++; /* cplinu for block 0 */
/* bit alloc info */
frame_bits += 2*4 + 3 + 6 + s->nb_channels * (4 + 3);
/* CRC */
frame_bits += 16;
/* now the big work begins : do the bit allocation. Modify the snr
offset until we can pack everything in the requested frame size */
csnroffst = s->csnroffst;
while (csnroffst >= 0 &&
bit_alloc(s, bap, encoded_exp, exp_strategy, frame_bits, csnroffst, 0) < 0)
csnroffst -= SNR_INC1;
if (csnroffst < 0) {
fprintf(stderr, "Error !!!\n");
return -1;
}
while ((csnroffst + SNR_INC1) <= 63 &&
bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits,
csnroffst + SNR_INC1, 0) >= 0) {
csnroffst += SNR_INC1;
memcpy(bap, bap1, sizeof(bap1));
}
while ((csnroffst + 1) <= 63 &&
bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits, csnroffst + 1, 0) >= 0) {
csnroffst++;
memcpy(bap, bap1, sizeof(bap1));
}
fsnroffst = 0;
while ((fsnroffst + SNR_INC1) <= 15 &&
bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits,
csnroffst, fsnroffst + SNR_INC1) >= 0) {
fsnroffst += SNR_INC1;
memcpy(bap, bap1, sizeof(bap1));
}
while ((fsnroffst + 1) <= 15 &&
bit_alloc(s, bap1, encoded_exp, exp_strategy, frame_bits,
csnroffst, fsnroffst + 1) >= 0) {
fsnroffst++;
memcpy(bap, bap1, sizeof(bap1));
}
s->csnroffst = csnroffst;
for(ch=0;ch<s->nb_channels;ch++)
s->fsnroffst[ch] = fsnroffst;
#if defined(DEBUG_BITALLOC)
{
int j;
for(i=0;i<6;i++) {
for(ch=0;ch<s->nb_channels;ch++) {
printf("Block #%d Ch%d:\n", i, ch);
printf("bap=");
for(j=0;j<s->nb_coefs[ch];j++) {
printf("%d ",bap[i][ch][j]);
}
printf("\n");
}
}
}
#endif
return 0;
}
static int AC3_encode_init(AVCodecContext *avctx)
{
int freq = avctx->sample_rate;
int bitrate = avctx->bit_rate;
int channels = avctx->channels;
AC3EncodeContext *s = avctx->priv_data;
int i, j, k, l, ch, v;
float alpha;
static unsigned short freqs[3] = { 48000, 44100, 32000 };
avctx->frame_size = AC3_FRAME_SIZE;
avctx->key_frame = 1; /* always key frame */
/* number of channels */
if (channels == 1)
s->acmod = 1;
else if (channels == 2)
s->acmod = 2;
else
return -1;
s->nb_channels = channels;
/* frequency */
for(i=0;i<3;i++) {
for(j=0;j<3;j++)
if ((freqs[j] >> i) == freq)
goto found;
}
return -1;
found:
s->sample_rate = freq;
s->halfratecod = i;
s->fscod = j;
s->bsid = 8 + s->halfratecod;
s->bsmod = 0; /* complete main audio service */
/* bitrate & frame size */
bitrate /= 1000;
for(i=0;i<19;i++) {
if ((bitratetab[i] >> s->halfratecod) == bitrate)
break;
}
if (i == 19)
return -1;
s->bit_rate = bitrate;
s->frmsizecod = i << 1;
s->frame_size_min = (bitrate * 1000 * AC3_FRAME_SIZE) / (freq * 16);
/* for now we do not handle fractional sizes */
s->frame_size = s->frame_size_min;
/* bit allocation init */
for(ch=0;ch<s->nb_channels;ch++) {
/* bandwidth for each channel */
/* XXX: should compute the bandwidth according to the frame
size, so that we avoid anoying high freq artefacts */
s->chbwcod[ch] = 50; /* sample bandwidth as mpeg audio layer 2 table 0 */
s->nb_coefs[ch] = ((s->chbwcod[ch] + 12) * 3) + 37;
}
/* initial snr offset */
s->csnroffst = 40;
/* compute bndtab and masktab from bandsz */
k = 0;
l = 0;
for(i=0;i<50;i++) {
bndtab[i] = l;
v = bndsz[i];
for(j=0;j<v;j++) masktab[k++]=i;
l += v;
}
bndtab[50] = 0;
/* mdct init */
fft_init(MDCT_NBITS - 2);
for(i=0;i<N/4;i++) {
alpha = 2 * M_PI * (i + 1.0 / 8.0) / (float)N;
xcos1[i] = fix15(-cos(alpha));
xsin1[i] = fix15(-sin(alpha));
}
ac3_crc_init();
return 0;
}
/* output the AC3 frame header */
static void output_frame_header(AC3EncodeContext *s, unsigned char *frame)
{
init_put_bits(&s->pb, frame, AC3_MAX_CODED_FRAME_SIZE, NULL, NULL);
put_bits(&s->pb, 16, 0x0b77); /* frame header */
put_bits(&s->pb, 16, 0); /* crc1: will be filled later */
put_bits(&s->pb, 2, s->fscod);
put_bits(&s->pb, 6, s->frmsizecod + (s->frame_size - s->frame_size_min));
put_bits(&s->pb, 5, s->bsid);
put_bits(&s->pb, 3, s->bsmod);
put_bits(&s->pb, 3, s->acmod);
if (s->acmod == 2) {
put_bits(&s->pb, 2, 0); /* surround not indicated */
}
put_bits(&s->pb, 1, 0); /* no LFE */
put_bits(&s->pb, 5, 31); /* dialog norm: -31 db */
put_bits(&s->pb, 1, 0); /* no compression control word */
put_bits(&s->pb, 1, 0); /* no lang code */
put_bits(&s->pb, 1, 0); /* no audio production info */
put_bits(&s->pb, 1, 0); /* no copyright */
put_bits(&s->pb, 1, 1); /* original bitstream */
put_bits(&s->pb, 1, 0); /* no time code 1 */
put_bits(&s->pb, 1, 0); /* no time code 2 */
put_bits(&s->pb, 1, 0); /* no addtional bit stream info */
}
/* symetric quantization on 'levels' levels */
static inline int sym_quant(int c, int e, int levels)
{
int v;
if (c >= 0) {
v = (levels * (c << e)) >> 25;
v = (levels >> 1) + v;
} else {
v = (levels * ((-c) << e)) >> 25;
v = (levels >> 1) - v;
}
assert (v >= 0 && v < levels);
return v;
}
/* asymetric quantization on 2^qbits levels */
static inline int asym_quant(int c, int e, int qbits)
{
int lshift, m, v;
lshift = e + qbits - 24;
if (lshift >= 0)
v = c << lshift;
else
v = c >> (-lshift);
/* rounding */
v = (v + 1) >> 1;
m = (1 << (qbits-1));
if (v >= m)
v = m - 1;
assert(v >= -m);
return v & ((1 << qbits)-1);
}
/* Output one audio block. There are NB_BLOCKS audio blocks in one AC3
frame */
static void output_audio_block(AC3EncodeContext *s,
UINT8 exp_strategy[AC3_MAX_CHANNELS],
UINT8 encoded_exp[AC3_MAX_CHANNELS][N/2],
UINT8 bap[AC3_MAX_CHANNELS][N/2],
INT32 mdct_coefs[AC3_MAX_CHANNELS][N/2],
INT8 global_exp[AC3_MAX_CHANNELS],
int block_num)
{
int ch, nb_groups, group_size, i, baie;
UINT8 *p;
UINT16 qmant[AC3_MAX_CHANNELS][N/2];
int exp0, exp1;
int mant1_cnt, mant2_cnt, mant4_cnt;
UINT16 *qmant1_ptr, *qmant2_ptr, *qmant4_ptr;
int delta0, delta1, delta2;
for(ch=0;ch<s->nb_channels;ch++)
put_bits(&s->pb, 1, 0); /* 512 point MDCT */
for(ch=0;ch<s->nb_channels;ch++)
put_bits(&s->pb, 1, 1); /* no dither */
put_bits(&s->pb, 1, 0); /* no dynamic range */
if (block_num == 0) {
/* for block 0, even if no coupling, we must say it. This is a
waste of bit :-) */
put_bits(&s->pb, 1, 1); /* coupling strategy present */
put_bits(&s->pb, 1, 0); /* no coupling strategy */
} else {
put_bits(&s->pb, 1, 0); /* no new coupling strategy */
}
if (s->acmod == 2) {
put_bits(&s->pb, 1, 0); /* no matrixing (but should be used in the future) */
}
#if defined(DEBUG)
{
static int count = 0;
printf("Block #%d (%d)\n", block_num, count++);
}
#endif
/* exponent strategy */
for(ch=0;ch<s->nb_channels;ch++) {
put_bits(&s->pb, 2, exp_strategy[ch]);
}
for(ch=0;ch<s->nb_channels;ch++) {
if (exp_strategy[ch] != EXP_REUSE)
put_bits(&s->pb, 6, s->chbwcod[ch]);
}
/* exponents */
for (ch = 0; ch < s->nb_channels; ch++) {
switch(exp_strategy[ch]) {
case EXP_REUSE:
continue;
case EXP_D15:
group_size = 1;
break;
case EXP_D25:
group_size = 2;
break;
default:
case EXP_D45:
group_size = 4;
break;
}
nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);
p = encoded_exp[ch];
/* first exponent */
exp1 = *p++;
put_bits(&s->pb, 4, exp1);
/* next ones are delta encoded */
for(i=0;i<nb_groups;i++) {
/* merge three delta in one code */
exp0 = exp1;
exp1 = p[0];
p += group_size;
delta0 = exp1 - exp0 + 2;
exp0 = exp1;
exp1 = p[0];
p += group_size;
delta1 = exp1 - exp0 + 2;
exp0 = exp1;
exp1 = p[0];
p += group_size;
delta2 = exp1 - exp0 + 2;
put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);
}
put_bits(&s->pb, 2, 0); /* no gain range info */
}
/* bit allocation info */
baie = (block_num == 0);
put_bits(&s->pb, 1, baie);
if (baie) {
put_bits(&s->pb, 2, s->sdecaycod);
put_bits(&s->pb, 2, s->fdecaycod);
put_bits(&s->pb, 2, s->sgaincod);
put_bits(&s->pb, 2, s->dbkneecod);
put_bits(&s->pb, 3, s->floorcod);
}
/* snr offset */
put_bits(&s->pb, 1, baie); /* always present with bai */
if (baie) {
put_bits(&s->pb, 6, s->csnroffst);
for(ch=0;ch<s->nb_channels;ch++) {
put_bits(&s->pb, 4, s->fsnroffst[ch]);
put_bits(&s->pb, 3, s->fgaincod[ch]);
}
}
put_bits(&s->pb, 1, 0); /* no delta bit allocation */
put_bits(&s->pb, 1, 0); /* no data to skip */
/* mantissa encoding : we use two passes to handle the grouping. A
one pass method may be faster, but it would necessitate to
modify the output stream. */
/* first pass: quantize */
mant1_cnt = mant2_cnt = mant4_cnt = 0;
qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;
for (ch = 0; ch < s->nb_channels; ch++) {
int b, c, e, v;
for(i=0;i<s->nb_coefs[ch];i++) {
c = mdct_coefs[ch][i];
e = encoded_exp[ch][i] - global_exp[ch];
b = bap[ch][i];
switch(b) {
case 0:
v = 0;
break;
case 1:
v = sym_quant(c, e, 3);
switch(mant1_cnt) {
case 0:
qmant1_ptr = &qmant[ch][i];
v = 9 * v;
mant1_cnt = 1;
break;
case 1:
*qmant1_ptr += 3 * v;
mant1_cnt = 2;
v = 128;
break;
default:
*qmant1_ptr += v;
mant1_cnt = 0;
v = 128;
break;
}
break;
case 2:
v = sym_quant(c, e, 5);
switch(mant2_cnt) {
case 0:
qmant2_ptr = &qmant[ch][i];
v = 25 * v;
mant2_cnt = 1;
break;
case 1:
*qmant2_ptr += 5 * v;
mant2_cnt = 2;
v = 128;
break;
default:
*qmant2_ptr += v;
mant2_cnt = 0;
v = 128;
break;
}
break;
case 3:
v = sym_quant(c, e, 7);
break;
case 4:
v = sym_quant(c, e, 11);
switch(mant4_cnt) {
case 0:
qmant4_ptr = &qmant[ch][i];
v = 11 * v;
mant4_cnt = 1;
break;
default:
*qmant4_ptr += v;
mant4_cnt = 0;
v = 128;
break;
}
break;
case 5:
v = sym_quant(c, e, 15);
break;
case 14:
v = asym_quant(c, e, 14);
break;
case 15:
v = asym_quant(c, e, 16);
break;
default:
v = asym_quant(c, e, b - 1);
break;
}
qmant[ch][i] = v;
}
}
/* second pass : output the values */
for (ch = 0; ch < s->nb_channels; ch++) {
int b, q;
for(i=0;i<s->nb_coefs[ch];i++) {
q = qmant[ch][i];
b = bap[ch][i];
switch(b) {
case 0:
break;
case 1:
if (q != 128)
put_bits(&s->pb, 5, q);
break;
case 2:
if (q != 128)
put_bits(&s->pb, 7, q);
break;
case 3:
put_bits(&s->pb, 3, q);
break;
case 4:
if (q != 128)
put_bits(&s->pb, 7, q);
break;
case 14:
put_bits(&s->pb, 14, q);
break;
case 15:
put_bits(&s->pb, 16, q);
break;
default:
put_bits(&s->pb, b - 1, q);
break;
}
}
}
}
/* compute the ac3 crc */
#define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))
static void ac3_crc_init(void)
{
unsigned int c, n, k;
for(n=0;n<256;n++) {
c = n << 8;
for (k = 0; k < 8; k++) {
if (c & (1 << 15))
c = ((c << 1) & 0xffff) ^ (CRC16_POLY & 0xffff);
else
c = c << 1;
}
crc_table[n] = c;
}
}
static unsigned int ac3_crc(UINT8 *data, int n, unsigned int crc)
{
int i;
for(i=0;i<n;i++) {
crc = (crc_table[data[i] ^ (crc >> 8)] ^ (crc << 8)) & 0xffff;
}
return crc;
}
static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)
{
unsigned int c;
c = 0;
while (a) {
if (a & 1)
c ^= b;
a = a >> 1;
b = b << 1;
if (b & (1 << 16))
b ^= poly;
}
return c;
}
static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)
{
unsigned int r;
r = 1;
while (n) {
if (n & 1)
r = mul_poly(r, a, poly);
a = mul_poly(a, a, poly);
n >>= 1;
}
return r;
}
/* compute log2(max(abs(tab[]))) */
static int log2_tab(INT16 *tab, int n)
{
int i, v;
v = 0;
for(i=0;i<n;i++) {
v |= abs(tab[i]);
}
return log2(v);
}
static void lshift_tab(INT16 *tab, int n, int lshift)
{
int i;
if (lshift > 0) {
for(i=0;i<n;i++) {
tab[i] <<= lshift;
}
} else if (lshift < 0) {
lshift = -lshift;
for(i=0;i<n;i++) {
tab[i] >>= lshift;
}
}
}
/* fill the end of the frame and compute the two crcs */
static int output_frame_end(AC3EncodeContext *s)
{
int frame_size, frame_size_58, n, crc1, crc2, crc_inv;
UINT8 *frame;
frame_size = s->frame_size; /* frame size in words */
/* align to 8 bits */
flush_put_bits(&s->pb);
/* add zero bytes to reach the frame size */
frame = s->pb.buf;
n = 2 * s->frame_size - (s->pb.buf_ptr - frame) - 2;
assert(n >= 0);
memset(s->pb.buf_ptr, 0, n);
/* Now we must compute both crcs : this is not so easy for crc1
because it is at the beginning of the data... */
frame_size_58 = (frame_size >> 1) + (frame_size >> 3);
crc1 = ac3_crc(frame + 4, (2 * frame_size_58) - 4, 0);
/* XXX: could precompute crc_inv */
crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);
crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);
frame[2] = crc1 >> 8;
frame[3] = crc1;
crc2 = ac3_crc(frame + 2 * frame_size_58, (frame_size - frame_size_58) * 2 - 2, 0);
frame[2*frame_size - 2] = crc2 >> 8;
frame[2*frame_size - 1] = crc2;
// printf("n=%d frame_size=%d\n", n, frame_size);
return frame_size * 2;
}
int AC3_encode_frame(AVCodecContext *avctx,
unsigned char *frame, int buf_size, void *data)
{
AC3EncodeContext *s = avctx->priv_data;
short *samples = data;
int i, j, k, v, ch;
INT16 input_samples[N];
INT32 mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
UINT8 exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
UINT8 exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];
UINT8 encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
UINT8 bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
INT8 exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];
int frame_bits;
frame_bits = 0;
for(ch=0;ch<s->nb_channels;ch++) {
/* fixed mdct to the six sub blocks & exponent computation */
for(i=0;i<NB_BLOCKS;i++) {
INT16 *sptr;
int sinc;
/* compute input samples */
memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(INT16));
sinc = s->nb_channels;
sptr = samples + (sinc * (N/2) * i) + ch;
for(j=0;j<N/2;j++) {
v = *sptr;
input_samples[j + N/2] = v;
s->last_samples[ch][j] = v;
sptr += sinc;
}
/* apply the MDCT window */
for(j=0;j<N/2;j++) {
input_samples[j] = MUL16(input_samples[j],
ac3_window[j]) >> 15;
input_samples[N-j-1] = MUL16(input_samples[N-j-1],
ac3_window[j]) >> 15;
}
/* Normalize the samples to use the maximum available
precision */
v = 14 - log2_tab(input_samples, N);
if (v < 0)
v = 0;
exp_samples[i][ch] = v - 8;
lshift_tab(input_samples, N, v);
/* do the MDCT */
mdct512(mdct_coef[i][ch], input_samples);
/* compute "exponents". We take into account the
normalization there */
for(j=0;j<N/2;j++) {
int e;
v = abs(mdct_coef[i][ch][j]);
if (v == 0)
e = 24;
else {
e = 23 - log2(v) + exp_samples[i][ch];
if (e >= 24) {
e = 24;
mdct_coef[i][ch][j] = 0;
}
}
exp[i][ch][j] = e;
}
}
compute_exp_strategy(exp_strategy, exp, ch);
/* compute the exponents as the decoder will see them. The
EXP_REUSE case must be handled carefully : we select the
min of the exponents */
i = 0;
while (i < NB_BLOCKS) {
j = i + 1;
while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {
exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);
j++;
}
frame_bits += encode_exp(encoded_exp[i][ch],
exp[i][ch], s->nb_coefs[ch],
exp_strategy[i][ch]);
/* copy encoded exponents for reuse case */
for(k=i+1;k<j;k++) {
memcpy(encoded_exp[k][ch], encoded_exp[i][ch],
s->nb_coefs[ch] * sizeof(UINT8));
}
i = j;
}
}
compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);
/* everything is known... let's output the frame */
output_frame_header(s, frame);
for(i=0;i<NB_BLOCKS;i++) {
output_audio_block(s, exp_strategy[i], encoded_exp[i],
bap[i], mdct_coef[i], exp_samples[i], i);
}
return output_frame_end(s);
}
#if 0
/*************************************************************************/
/* TEST */
#define FN (N/4)
void fft_test(void)
{
IComplex in[FN], in1[FN];
int k, n, i;
float sum_re, sum_im, a;
/* FFT test */
for(i=0;i<FN;i++) {
in[i].re = random() % 65535 - 32767;
in[i].im = random() % 65535 - 32767;
in1[i] = in[i];
}
fft(in, 7);
/* do it by hand */
for(k=0;k<FN;k++) {
sum_re = 0;
sum_im = 0;
for(n=0;n<FN;n++) {
a = -2 * M_PI * (n * k) / FN;
sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);
sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);
}
printf("%3d: %6d,%6d %6.0f,%6.0f\n",
k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);
}
}
void mdct_test(void)
{
INT16 input[N];
INT32 output[N/2];
float input1[N];
float output1[N/2];
float s, a, err, e, emax;
int i, k, n;
for(i=0;i<N;i++) {
input[i] = (random() % 65535 - 32767) * 9 / 10;
input1[i] = input[i];
}
mdct512(output, input);
/* do it by hand */
for(k=0;k<N/2;k++) {
s = 0;
for(n=0;n<N;n++) {
a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));
s += input1[n] * cos(a);
}
output1[k] = -2 * s / N;
}
err = 0;
emax = 0;
for(i=0;i<N/2;i++) {
printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);
e = output[i] - output1[i];
if (e > emax)
emax = e;
err += e * e;
}
printf("err2=%f emax=%f\n", err / (N/2), emax);
}
void test_ac3(void)
{
AC3EncodeContext ctx;
unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];
short samples[AC3_FRAME_SIZE];
int ret, i;
AC3_encode_init(&ctx, 44100, 64000, 1);
fft_test();
mdct_test();
for(i=0;i<AC3_FRAME_SIZE;i++)
samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);
ret = AC3_encode_frame(&ctx, frame, samples);
printf("ret=%d\n", ret);
}
#endif
AVCodec ac3_encoder = {
"ac3",
CODEC_TYPE_AUDIO,
CODEC_ID_AC3,
sizeof(AC3EncodeContext),
AC3_encode_init,
AC3_encode_frame,
NULL,
};
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