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FFmpeg/libavcodec/ac3enc.c

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/*
* The simplest AC3 encoder
* 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 ac3enc.c
* The simplest AC3 encoder.
*/
//#define DEBUG
//#define DEBUG_BITALLOC
#include "libavutil/crc.h"
#include "avcodec.h"
#include "bitstream.h"
#include "ac3.h"
typedef struct AC3EncodeContext {
PutBitContext pb;
int nb_channels;
int nb_all_channels;
int lfe_channel;
int bit_rate;
unsigned int sample_rate;
unsigned int bitstream_id;
unsigned int frame_size_min; /* minimum frame size in case rounding is necessary */
unsigned int frame_size; /* current frame size in words */
unsigned int bits_written;
unsigned int samples_written;
int sr_shift;
unsigned int frame_size_code;
unsigned int sr_code; /* frequency */
unsigned int channel_mode;
int lfe;
unsigned int bitstream_mode;
short last_samples[AC3_MAX_CHANNELS][256];
unsigned int chbwcod[AC3_MAX_CHANNELS];
int nb_coefs[AC3_MAX_CHANNELS];
/* bitrate allocation control */
int slow_gain_code, slow_decay_code, fast_decay_code, db_per_bit_code, floor_code;
AC3BitAllocParameters bit_alloc;
int coarse_snr_offset;
int fast_gain_code[AC3_MAX_CHANNELS];
int fine_snr_offset[AC3_MAX_CHANNELS];
/* mantissa encoding */
int mant1_cnt, mant2_cnt, mant4_cnt;
} AC3EncodeContext;
static int16_t costab[64];
static int16_t sintab[64];
static int16_t xcos1[128];
static int16_t xsin1[128];
#define MDCT_NBITS 9
#define N (1 << MDCT_NBITS)
/* new exponents are sent if their Norm 1 exceed this number */
#define EXP_DIFF_THRESHOLD 1000
static inline int16_t fix15(float a)
{
int v;
v = (int)(a * (float)(1 << 15));
if (v < -32767)
v = -32767;
else if (v > 32767)
v = 32767;
return v;
}
typedef struct IComplex {
short re,im;
} IComplex;
static void fft_init(int ln)
{
int i, 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));
}
}
/* 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 = ff_reverse[j] >> (8 - ln);
if (k < j)
FFSWAP(IComplex, z[k], z[j]);
}
/* 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_t *out, int16_t *in)
{
int i, re, im, re1, im1;
int16_t 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_t *exp1, uint8_t *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_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
int ch, int is_lfe)
{
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
av_log(NULL, AV_LOG_DEBUG, "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;
}
if (is_lfe)
return;
/* 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_t exp[N/2], uint8_t 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_t encoded_exp[N/2],
uint8_t exp[N/2],
int nb_exps,
int exp_strategy)
{
int group_size, nb_groups, i, j, k, exp_min;
uint8_t 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;
/* Decrease the delta between each groups to within 2
* so that they can be differentially encoded */
for (i=1;i<=nb_groups;i++)
exp1[i] = FFMIN(exp1[i], exp1[i-1] + 2);
for (i=nb_groups-1;i>=0;i--)
exp1[i] = FFMIN(exp1[i], exp1[i+1] + 2);
/* 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)
av_log(NULL, AV_LOG_DEBUG, "exponents: strategy=%d\n", exp_strategy);
for(i=0;i<=nb_groups * group_size;i++) {
av_log(NULL, AV_LOG_DEBUG, "%d ", encoded_exp[i]);
}
av_log(NULL, AV_LOG_DEBUG, "\n");
#endif
return 4 + (nb_groups / 3) * 7;
}
/* return the size in bits taken by the mantissa */
static int compute_mantissa_size(AC3EncodeContext *s, uint8_t *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 void bit_alloc_masking(AC3EncodeContext *s,
uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50])
{
int blk, ch;
int16_t band_psd[NB_BLOCKS][AC3_MAX_CHANNELS][50];
for(blk=0; blk<NB_BLOCKS; blk++) {
for(ch=0;ch<s->nb_all_channels;ch++) {
if(exp_strategy[blk][ch] == EXP_REUSE) {
memcpy(psd[blk][ch], psd[blk-1][ch], (N/2)*sizeof(int16_t));
memcpy(mask[blk][ch], mask[blk-1][ch], 50*sizeof(int16_t));
} else {
ff_ac3_bit_alloc_calc_psd(encoded_exp[blk][ch], 0,
s->nb_coefs[ch],
psd[blk][ch], band_psd[blk][ch]);
ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, band_psd[blk][ch],
0, s->nb_coefs[ch],
ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],
ch == s->lfe_channel,
DBA_NONE, 0, NULL, NULL, NULL,
mask[blk][ch]);
}
}
}
}
static int bit_alloc(AC3EncodeContext *s,
int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50],
int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
int frame_bits, int coarse_snr_offset, int fine_snr_offset)
{
int i, ch;
int snr_offset;
snr_offset = (((coarse_snr_offset - 15) << 4) + fine_snr_offset) << 2;
/* 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_all_channels;ch++) {
ff_ac3_bit_alloc_calc_bap(mask[i][ch], psd[i][ch], 0,
s->nb_coefs[ch], snr_offset,
s->bit_alloc.floor, ff_ac3_bap_tab,
bap[i][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",
coarse_snr_offset, fine_snr_offset, 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_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
int frame_bits)
{
int i, ch;
int coarse_snr_offset, fine_snr_offset;
uint8_t bap1[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50];
static const int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };
/* init default parameters */
s->slow_decay_code = 2;
s->fast_decay_code = 1;
s->slow_gain_code = 1;
s->db_per_bit_code = 2;
s->floor_code = 4;
for(ch=0;ch<s->nb_all_channels;ch++)
s->fast_gain_code[ch] = 4;
/* compute real values */
s->bit_alloc.sr_code = s->sr_code;
s->bit_alloc.sr_shift = s->sr_shift;
s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->sr_shift;
s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->sr_shift;
s->bit_alloc.slow_gain = ff_ac3_slow_gain_tab[s->slow_gain_code];
s->bit_alloc.db_per_bit = ff_ac3_db_per_bit_tab[s->db_per_bit_code];
s->bit_alloc.floor = ff_ac3_floor_tab[s->floor_code];
/* header size */
frame_bits += 65;
// if (s->channel_mode == 2)
// frame_bits += 2;
frame_bits += frame_bits_inc[s->channel_mode];
/* audio blocks */
for(i=0;i<NB_BLOCKS;i++) {
frame_bits += s->nb_channels * 2 + 2; /* blksw * c, dithflag * c, dynrnge, cplstre */
if (s->channel_mode == AC3_CHMODE_STEREO) {
frame_bits++; /* rematstr */
if(i==0) frame_bits += 4;
}
frame_bits += 2 * s->nb_channels; /* chexpstr[2] * c */
if (s->lfe)
frame_bits++; /* lfeexpstr */
for(ch=0;ch<s->nb_channels;ch++) {
if (exp_strategy[i][ch] != EXP_REUSE)
frame_bits += 6 + 2; /* chbwcod[6], gainrng[2] */
}
frame_bits++; /* baie */
frame_bits++; /* snr */
frame_bits += 2; /* delta / skip */
}
frame_bits++; /* cplinu for block 0 */
/* bit alloc info */
/* sdcycod[2], fdcycod[2], sgaincod[2], dbpbcod[2], floorcod[3] */
/* csnroffset[6] */
/* (fsnoffset[4] + fgaincod[4]) * c */
frame_bits += 2*4 + 3 + 6 + s->nb_all_channels * (4 + 3);
/* auxdatae, crcrsv */
frame_bits += 2;
/* CRC */
frame_bits += 16;
/* calculate psd and masking curve before doing bit allocation */
bit_alloc_masking(s, encoded_exp, exp_strategy, psd, mask);
/* now the big work begins : do the bit allocation. Modify the snr
offset until we can pack everything in the requested frame size */
coarse_snr_offset = s->coarse_snr_offset;
while (coarse_snr_offset >= 0 &&
bit_alloc(s, mask, psd, bap, frame_bits, coarse_snr_offset, 0) < 0)
coarse_snr_offset -= SNR_INC1;
if (coarse_snr_offset < 0) {
av_log(NULL, AV_LOG_ERROR, "Bit allocation failed. Try increasing the bitrate.\n");
return -1;
}
while ((coarse_snr_offset + SNR_INC1) <= 63 &&
bit_alloc(s, mask, psd, bap1, frame_bits,
coarse_snr_offset + SNR_INC1, 0) >= 0) {
coarse_snr_offset += SNR_INC1;
memcpy(bap, bap1, sizeof(bap1));
}
while ((coarse_snr_offset + 1) <= 63 &&
bit_alloc(s, mask, psd, bap1, frame_bits, coarse_snr_offset + 1, 0) >= 0) {
coarse_snr_offset++;
memcpy(bap, bap1, sizeof(bap1));
}
fine_snr_offset = 0;
while ((fine_snr_offset + SNR_INC1) <= 15 &&
bit_alloc(s, mask, psd, bap1, frame_bits,
coarse_snr_offset, fine_snr_offset + SNR_INC1) >= 0) {
fine_snr_offset += SNR_INC1;
memcpy(bap, bap1, sizeof(bap1));
}
while ((fine_snr_offset + 1) <= 15 &&
bit_alloc(s, mask, psd, bap1, frame_bits,
coarse_snr_offset, fine_snr_offset + 1) >= 0) {
fine_snr_offset++;
memcpy(bap, bap1, sizeof(bap1));
}
s->coarse_snr_offset = coarse_snr_offset;
for(ch=0;ch<s->nb_all_channels;ch++)
s->fine_snr_offset[ch] = fine_snr_offset;
#if defined(DEBUG_BITALLOC)
{
int j;
for(i=0;i<6;i++) {
for(ch=0;ch<s->nb_all_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 av_cold 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, ch;
float alpha;
int bw_code;
static const uint8_t channel_mode_defs[6] = {
0x01, /* C */
0x02, /* L R */
0x03, /* L C R */
0x06, /* L R SL SR */
0x07, /* L C R SL SR */
0x07, /* L C R SL SR (+LFE) */
};
avctx->frame_size = AC3_FRAME_SIZE;
ac3_common_init();
/* number of channels */
if (channels < 1 || channels > 6)
return -1;
s->channel_mode = channel_mode_defs[channels - 1];
s->lfe = (channels == 6) ? 1 : 0;
s->nb_all_channels = channels;
s->nb_channels = channels > 5 ? 5 : channels;
s->lfe_channel = s->lfe ? 5 : -1;
/* frequency */
for(i=0;i<3;i++) {
for(j=0;j<3;j++)
if ((ff_ac3_sample_rate_tab[j] >> i) == freq)
goto found;
}
return -1;
found:
s->sample_rate = freq;
s->sr_shift = i;
s->sr_code = j;
s->bitstream_id = 8 + s->sr_shift;
s->bitstream_mode = 0; /* complete main audio service */
/* bitrate & frame size */
for(i=0;i<19;i++) {
if ((ff_ac3_bitrate_tab[i] >> s->sr_shift)*1000 == bitrate)
break;
}
if (i == 19)
return -1;
s->bit_rate = bitrate;
s->frame_size_code = i << 1;
s->frame_size_min = ff_ac3_frame_size_tab[s->frame_size_code][s->sr_code];
s->bits_written = 0;
s->samples_written = 0;
s->frame_size = s->frame_size_min;
/* bit allocation init */
if(avctx->cutoff) {
/* calculate bandwidth based on user-specified cutoff frequency */
int cutoff = av_clip(avctx->cutoff, 1, s->sample_rate >> 1);
int fbw_coeffs = cutoff * 512 / s->sample_rate;
bw_code = av_clip((fbw_coeffs - 73) / 3, 0, 60);
} else {
/* use default bandwidth setting */
/* XXX: should compute the bandwidth according to the frame
size, so that we avoid annoying high frequency artifacts */
bw_code = 50;
}
for(ch=0;ch<s->nb_channels;ch++) {
/* bandwidth for each channel */
s->chbwcod[ch] = bw_code;
s->nb_coefs[ch] = bw_code * 3 + 73;
}
if (s->lfe) {
s->nb_coefs[s->lfe_channel] = 7; /* fixed */
}
/* initial snr offset */
s->coarse_snr_offset = 40;
/* 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));
}
avctx->coded_frame= avcodec_alloc_frame();
avctx->coded_frame->key_frame= 1;
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);
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->sr_code);
put_bits(&s->pb, 6, s->frame_size_code + (s->frame_size - s->frame_size_min));
put_bits(&s->pb, 5, s->bitstream_id);
put_bits(&s->pb, 3, s->bitstream_mode);
put_bits(&s->pb, 3, s->channel_mode);
if ((s->channel_mode & 0x01) && s->channel_mode != AC3_CHMODE_MONO)
put_bits(&s->pb, 2, 1); /* XXX -4.5 dB */
if (s->channel_mode & 0x04)
put_bits(&s->pb, 2, 1); /* XXX -6 dB */
if (s->channel_mode == AC3_CHMODE_STEREO)
put_bits(&s->pb, 2, 0); /* surround not indicated */
put_bits(&s->pb, 1, s->lfe); /* 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 additional 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)) >> 24;
v = (v + 1) >> 1;
v = (levels >> 1) + v;
} else {
v = (levels * ((-c) << e)) >> 24;
v = (v + 1) >> 1;
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_t exp_strategy[AC3_MAX_CHANNELS],
uint8_t encoded_exp[AC3_MAX_CHANNELS][N/2],
uint8_t bap[AC3_MAX_CHANNELS][N/2],
int32_t mdct_coefs[AC3_MAX_CHANNELS][N/2],
int8_t global_exp[AC3_MAX_CHANNELS],
int block_num)
{
int ch, nb_groups, group_size, i, baie, rbnd;
uint8_t *p;
uint16_t qmant[AC3_MAX_CHANNELS][N/2];
int exp0, exp1;
int mant1_cnt, mant2_cnt, mant4_cnt;
uint16_t *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->channel_mode == AC3_CHMODE_STEREO)
{
if(block_num==0)
{
/* first block must define rematrixing (rematstr) */
put_bits(&s->pb, 1, 1);
/* dummy rematrixing rematflg(1:4)=0 */
for (rbnd=0;rbnd<4;rbnd++)
put_bits(&s->pb, 1, 0);
}
else
{
/* no matrixing (but should be used in the future) */
put_bits(&s->pb, 1, 0);
}
}
#if defined(DEBUG)
{
static int count = 0;
av_log(NULL, AV_LOG_DEBUG, "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]);
}
if (s->lfe) {
put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);
}
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_all_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);
}
if (ch != s->lfe_channel)
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->slow_decay_code);
put_bits(&s->pb, 2, s->fast_decay_code);
put_bits(&s->pb, 2, s->slow_gain_code);
put_bits(&s->pb, 2, s->db_per_bit_code);
put_bits(&s->pb, 3, s->floor_code);
}
/* snr offset */
put_bits(&s->pb, 1, baie); /* always present with bai */
if (baie) {
put_bits(&s->pb, 6, s->coarse_snr_offset);
for(ch=0;ch<s->nb_all_channels;ch++) {
put_bits(&s->pb, 4, s->fine_snr_offset[ch]);
put_bits(&s->pb, 3, s->fast_gain_code[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_all_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_all_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;
}
}
}
}
#define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))
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_t *tab, int n)
{
int i, v;
v = 0;
for(i=0;i<n;i++) {
v |= abs(tab[i]);
}
return av_log2(v);
}
static void lshift_tab(int16_t *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_t *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 - (pbBufPtr(&s->pb) - frame) - 2;
assert(n >= 0);
if(n>0)
memset(pbBufPtr(&s->pb), 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 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,
frame + 4, 2 * frame_size_58 - 4));
/* 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);
AV_WB16(frame+2,crc1);
crc2 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,
frame + 2 * frame_size_58,
(frame_size - frame_size_58) * 2 - 2));
AV_WB16(frame+2*frame_size-2,crc2);
// printf("n=%d frame_size=%d\n", n, frame_size);
return frame_size * 2;
}
static int AC3_encode_frame(AVCodecContext *avctx,
unsigned char *frame, int buf_size, void *data)
{
AC3EncodeContext *s = avctx->priv_data;
int16_t *samples = data;
int i, j, k, v, ch;
int16_t input_samples[N];
int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];
uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];
int frame_bits;
frame_bits = 0;
for(ch=0;ch<s->nb_all_channels;ch++) {
/* fixed mdct to the six sub blocks & exponent computation */
for(i=0;i<NB_BLOCKS;i++) {
int16_t *sptr;
int sinc;
/* compute input samples */
memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));
sinc = s->nb_all_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],
ff_ac3_window[j]) >> 15;
input_samples[N-j-1] = MUL16(input_samples[N-j-1],
ff_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 - 9;
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 - av_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, ch == s->lfe_channel);
/* 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_t));
}
i = j;
}
}
/* adjust for fractional frame sizes */
while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {
s->bits_written -= s->bit_rate;
s->samples_written -= s->sample_rate;
}
s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
s->bits_written += s->frame_size * 16;
s->samples_written += AC3_FRAME_SIZE;
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);
}
static av_cold int AC3_encode_close(AVCodecContext *avctx)
{
av_freep(&avctx->coded_frame);
return 0;
}
#if 0
/*************************************************************************/
/* TEST */
#undef random
#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_t input[N];
int32_t 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,
AC3_encode_close,
NULL,
.sample_fmts = (enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},
.long_name = NULL_IF_CONFIG_SMALL("ATSC A/52 / AC-3"),
};