virtualenv/FFmpeg
1
0
Fork 0
mirror of https://github.com/FFmpeg/FFmpeg.git synced 2024-11-26 19:01:44 +02:00
Code Issues Releases Activity
14166a6d6c
FFmpeg/libavcodec/ac3enc.c
Justin Ruggles 14166a6d6c Remove avctx from AC3MDCTContext and just pass it to mdct_init() instead. 
Originally committed as revision 26170 to svn://svn.ffmpeg.org/ffmpeg/trunk
2010-12-30 22:13:30 +00:00

2083 lines
63 KiB
C
Raw Blame History

/*
* The simplest AC-3 encoder
* Copyright (c) 2000 Fabrice Bellard
* Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
* Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
*
* 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
* The simplest AC-3 encoder.
*/
//#define DEBUG
#include "libavcore/audioconvert.h"
#include "libavutil/crc.h"
#include "avcodec.h"
#include "put_bits.h"
#include "dsputil.h"
#include "ac3.h"
#include "audioconvert.h"
/** Maximum number of exponent groups. +1 for separate DC exponent. */
#define AC3_MAX_EXP_GROUPS 85
/** Scale a float value by 2^bits and convert to an integer. */
#define SCALE_FLOAT(a, bits) lrintf((a) * (float)(1 << (bits)))
/** Scale a float value by 2^15, convert to an integer, and clip to range -32767..32767. */
#define FIX15(a) av_clip(SCALE_FLOAT(a, 15), -32767, 32767)
/**
* Compex number.
* Used in fixed-point MDCT calculation.
*/
typedef struct IComplex {
int16_t re,im;
} IComplex;
typedef struct AC3MDCTContext {
int nbits; ///< log2(transform size)
int16_t *costab; ///< FFT cos table
int16_t *sintab; ///< FFT sin table
int16_t *xcos1; ///< MDCT cos table
int16_t *xsin1; ///< MDCT sin table
int16_t *rot_tmp; ///< temp buffer for pre-rotated samples
IComplex *cplx_tmp; ///< temp buffer for complex pre-rotated samples
} AC3MDCTContext;
/**
* Data for a single audio block.
*/
typedef struct AC3Block {
uint8_t **bap; ///< bit allocation pointers (bap)
int32_t **mdct_coef; ///< MDCT coefficients
uint8_t **exp; ///< original exponents
uint8_t **grouped_exp; ///< grouped exponents
int16_t **psd; ///< psd per frequency bin
int16_t **band_psd; ///< psd per critical band
int16_t **mask; ///< masking curve
uint16_t **qmant; ///< quantized mantissas
uint8_t exp_strategy[AC3_MAX_CHANNELS]; ///< exponent strategies
int8_t exp_shift[AC3_MAX_CHANNELS]; ///< exponent shift values
} AC3Block;
/**
* AC-3 encoder private context.
*/
typedef struct AC3EncodeContext {
PutBitContext pb; ///< bitstream writer context
DSPContext dsp;
AC3MDCTContext mdct; ///< MDCT context
AC3Block blocks[AC3_MAX_BLOCKS]; ///< per-block info
int bitstream_id; ///< bitstream id (bsid)
int bitstream_mode; ///< bitstream mode (bsmod)
int bit_rate; ///< target bit rate, in bits-per-second
int sample_rate; ///< sampling frequency, in Hz
int frame_size_min; ///< minimum frame size in case rounding is necessary
int frame_size; ///< current frame size in bytes
int frame_size_code; ///< frame size code (frmsizecod)
uint16_t crc_inv[2];
int bits_written; ///< bit count (used to avg. bitrate)
int samples_written; ///< sample count (used to avg. bitrate)
int fbw_channels; ///< number of full-bandwidth channels (nfchans)
int channels; ///< total number of channels (nchans)
int lfe_on; ///< indicates if there is an LFE channel (lfeon)
int lfe_channel; ///< channel index of the LFE channel
int channel_mode; ///< channel mode (acmod)
const uint8_t *channel_map; ///< channel map used to reorder channels
int cutoff; ///< user-specified cutoff frequency, in Hz
int bandwidth_code[AC3_MAX_CHANNELS]; ///< bandwidth code (0 to 60) (chbwcod)
int nb_coefs[AC3_MAX_CHANNELS];
/* bitrate allocation control */
int slow_gain_code; ///< slow gain code (sgaincod)
int slow_decay_code; ///< slow decay code (sdcycod)
int fast_decay_code; ///< fast decay code (fdcycod)
int db_per_bit_code; ///< dB/bit code (dbpbcod)
int floor_code; ///< floor code (floorcod)
AC3BitAllocParameters bit_alloc; ///< bit allocation parameters
int coarse_snr_offset; ///< coarse SNR offsets (csnroffst)
int fast_gain_code[AC3_MAX_CHANNELS]; ///< fast gain codes (signal-to-mask ratio) (fgaincod)
int fine_snr_offset[AC3_MAX_CHANNELS]; ///< fine SNR offsets (fsnroffst)
int frame_bits_fixed; ///< number of non-coefficient bits for fixed parameters
int frame_bits; ///< all frame bits except exponents and mantissas
int exponent_bits; ///< number of bits used for exponents
/* mantissa encoding */
int mant1_cnt, mant2_cnt, mant4_cnt; ///< mantissa counts for bap=1,2,4
uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr; ///< mantissa pointers for bap=1,2,4
int16_t **planar_samples;
uint8_t *bap_buffer;
uint8_t *bap1_buffer;
int32_t *mdct_coef_buffer;
uint8_t *exp_buffer;
uint8_t *grouped_exp_buffer;
int16_t *psd_buffer;
int16_t *band_psd_buffer;
int16_t *mask_buffer;
uint16_t *qmant_buffer;
DECLARE_ALIGNED(16, int16_t, windowed_samples)[AC3_WINDOW_SIZE];
} AC3EncodeContext;
/**
* LUT for number of exponent groups.
* exponent_group_tab[exponent strategy-1][number of coefficients]
*/
static uint8_t exponent_group_tab[3][256];
/**
* Adjust the frame size to make the average bit rate match the target bit rate.
* This is only needed for 11025, 22050, and 44100 sample rates.
*/
static void adjust_frame_size(AC3EncodeContext *s)
{
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 +
2 * (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
s->bits_written += s->frame_size * 8;
s->samples_written += AC3_FRAME_SIZE;
}
/**
* Deinterleave input samples.
* Channels are reordered from FFmpeg's default order to AC-3 order.
*/
static void deinterleave_input_samples(AC3EncodeContext *s,
const int16_t *samples)
{
int ch, i;
/* deinterleave and remap input samples */
for (ch = 0; ch < s->channels; ch++) {
const int16_t *sptr;
int sinc;
/* copy last 256 samples of previous frame to the start of the current frame */
memcpy(&s->planar_samples[ch][0], &s->planar_samples[ch][AC3_FRAME_SIZE],
AC3_BLOCK_SIZE * sizeof(s->planar_samples[0][0]));
/* deinterleave */
sinc = s->channels;
sptr = samples + s->channel_map[ch];
for (i = AC3_BLOCK_SIZE; i < AC3_FRAME_SIZE+AC3_BLOCK_SIZE; i++) {
s->planar_samples[ch][i] = *sptr;
sptr += sinc;
}
}
}
/**
* Finalize MDCT and free allocated memory.
*/
static av_cold void mdct_end(AC3MDCTContext *mdct)
{
mdct->nbits = 0;
av_freep(&mdct->costab);
av_freep(&mdct->sintab);
av_freep(&mdct->xcos1);
av_freep(&mdct->xsin1);
av_freep(&mdct->rot_tmp);
av_freep(&mdct->cplx_tmp);
}
/**
* Initialize FFT tables.
* @param ln log2(FFT size)
*/
static av_cold int fft_init(AVCodecContext *avctx, AC3MDCTContext *mdct, int ln)
{
int i, n, n2;
float alpha;
n = 1 << ln;
n2 = n >> 1;
FF_ALLOC_OR_GOTO(avctx, mdct->costab, n2 * sizeof(*mdct->costab),
fft_alloc_fail);
FF_ALLOC_OR_GOTO(avctx, mdct->sintab, n2 * sizeof(*mdct->sintab),
fft_alloc_fail);
for (i = 0; i < n2; i++) {
alpha = 2.0 * M_PI * i / n;
mdct->costab[i] = FIX15(cos(alpha));
mdct->sintab[i] = FIX15(sin(alpha));
}
return 0;
fft_alloc_fail:
mdct_end(mdct);
return AVERROR(ENOMEM);
}
/**
* Initialize MDCT tables.
* @param nbits log2(MDCT size)
*/
static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct, int nbits)
{
int i, n, n4, ret;
n = 1 << nbits;
n4 = n >> 2;
mdct->nbits = nbits;
ret = fft_init(avctx, mdct, nbits - 2);
if (ret)
return ret;
FF_ALLOC_OR_GOTO(avctx, mdct->xcos1, n4 * sizeof(*mdct->xcos1),
mdct_alloc_fail);
FF_ALLOC_OR_GOTO(avctx, mdct->xsin1, n4 * sizeof(*mdct->xsin1),
mdct_alloc_fail);
FF_ALLOC_OR_GOTO(avctx, mdct->rot_tmp, n * sizeof(*mdct->rot_tmp),
mdct_alloc_fail);
FF_ALLOC_OR_GOTO(avctx, mdct->cplx_tmp, n4 * sizeof(*mdct->cplx_tmp),
mdct_alloc_fail);
for (i = 0; i < n4; i++) {
float alpha = 2.0 * M_PI * (i + 1.0 / 8.0) / n;
mdct->xcos1[i] = FIX15(-cos(alpha));
mdct->xsin1[i] = FIX15(-sin(alpha));
}
return 0;
mdct_alloc_fail:
mdct_end(mdct);
return AVERROR(ENOMEM);
}
/** Butterfly 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; \
}
/** Complex multiply */
#define CMUL(pre, pim, are, aim, bre, bim) \
{ \
pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15; \
pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15; \
}
/**
* Calculate a 2^n point complex FFT on 2^ln points.
* @param z complex input/output samples
* @param ln log2(FFT size)
*/
static void fft(AC3MDCTContext *mdct, 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 = av_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);
/* 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);
/* 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, mdct->costab[l], -mdct->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);
}
/**
* Calculate a 512-point MDCT
* @param out 256 output frequency coefficients
* @param in 512 windowed input audio samples
*/
static void mdct512(AC3MDCTContext *mdct, int32_t *out, int16_t *in)
{
int i, re, im, n, n2, n4;
int16_t *rot = mdct->rot_tmp;
IComplex *x = mdct->cplx_tmp;
n = 1 << mdct->nbits;
n2 = n >> 1;
n4 = n >> 2;
/* shift to simplify computations */
for (i = 0; i <n4; i++)
rot[i] = -in[i + 3*n4];
memcpy(&rot[n4], &in[0], 3*n4*sizeof(*in));
/* pre rotation */
for (i = 0; i < n4; i++) {
re = ((int)rot[ 2*i] - (int)rot[ n-1-2*i]) >> 1;
im = -((int)rot[n2+2*i] - (int)rot[n2-1-2*i]) >> 1;
CMUL(x[i].re, x[i].im, re, im, -mdct->xcos1[i], mdct->xsin1[i]);
}
fft(mdct, x, mdct->nbits - 2);
/* post rotation */
for (i = 0; i < n4; i++) {
re = x[i].re;
im = x[i].im;
CMUL(out[n2-1-2*i], out[2*i], re, im, mdct->xsin1[i], mdct->xcos1[i]);
}
}
/**
* Apply KBD window to input samples prior to MDCT.
*/
static void apply_window(int16_t *output, const int16_t *input,
const int16_t *window, int n)
{
int i;
int n2 = n >> 1;
for (i = 0; i < n2; i++) {
output[i] = MUL16(input[i], window[i]) >> 15;
output[n-i-1] = MUL16(input[n-i-1], window[i]) >> 15;
}
}
/**
* Calculate the log2() of the maximum absolute value in an array.
* @param tab input array
* @param n number of values in the array
* @return 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);
}
/**
* Left-shift each value in an array by a specified amount.
* @param tab input array
* @param n number of values in the array
* @param lshift left shift amount. a negative value means right shift.
*/
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;
}
}
/**
* Normalize the input samples to use the maximum available precision.
* This assumes signed 16-bit input samples. Exponents are reduced by 9 to
* match the 24-bit internal precision for MDCT coefficients.
*
* @return exponent shift
*/
static int normalize_samples(AC3EncodeContext *s)
{
int v = 14 - log2_tab(s->windowed_samples, AC3_WINDOW_SIZE);
v = FFMAX(0, v);
lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
return v - 9;
}
/**
* Apply the MDCT to input samples to generate frequency coefficients.
* This applies the KBD window and normalizes the input to reduce precision
* loss due to fixed-point calculations.
*/
static void apply_mdct(AC3EncodeContext *s)
{
int blk, ch;
for (ch = 0; ch < s->channels; ch++) {
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
const int16_t *input_samples = &s->planar_samples[ch][blk * AC3_BLOCK_SIZE];
apply_window(s->windowed_samples, input_samples, ff_ac3_window, AC3_WINDOW_SIZE);
block->exp_shift[ch] = normalize_samples(s);
mdct512(&s->mdct, block->mdct_coef[ch], s->windowed_samples);
}
}
}
/**
* Initialize exponent tables.
*/
static av_cold void exponent_init(AC3EncodeContext *s)
{
int i;
for (i = 73; i < 256; i++) {
exponent_group_tab[0][i] = (i - 1) / 3;
exponent_group_tab[1][i] = (i + 2) / 6;
exponent_group_tab[2][i] = (i + 8) / 12;
}
/* LFE */
exponent_group_tab[0][7] = 2;
}
/**
* Extract exponents from the MDCT coefficients.
* This takes into account the normalization that was done to the input samples
* by adjusting the exponents by the exponent shift values.
*/
static void extract_exponents(AC3EncodeContext *s)
{
int blk, ch, i;
for (ch = 0; ch < s->channels; ch++) {
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
for (i = 0; i < AC3_MAX_COEFS; i++) {
int e;
int v = abs(block->mdct_coef[ch][i]);
if (v == 0)
e = 24;
else {
e = 23 - av_log2(v) + block->exp_shift[ch];
if (e >= 24) {
e = 24;
block->mdct_coef[ch][i] = 0;
}
}
block->exp[ch][i] = e;
}
}
}
}
/**
* Exponent Difference Threshold.
* New exponents are sent if their SAD exceed this number.
*/
#define EXP_DIFF_THRESHOLD 1000
/**
* Calculate exponent strategies for all blocks in a single channel.
*/
static void compute_exp_strategy_ch(AC3EncodeContext *s, uint8_t *exp_strategy, uint8_t **exp)
{
int blk, blk1;
int exp_diff;
/* estimate if the exponent variation & decide if they should be
reused in the next frame */
exp_strategy[0] = EXP_NEW;
for (blk = 1; blk < AC3_MAX_BLOCKS; blk++) {
exp_diff = s->dsp.sad[0](NULL, exp[blk], exp[blk-1], 16, 16);
if (exp_diff > EXP_DIFF_THRESHOLD)
exp_strategy[blk] = EXP_NEW;
else
exp_strategy[blk] = EXP_REUSE;
}
emms_c();
/* now select the encoding strategy type : if exponents are often
recoded, we use a coarse encoding */
blk = 0;
while (blk < AC3_MAX_BLOCKS) {
blk1 = blk + 1;
while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1] == EXP_REUSE)
blk1++;
switch (blk1 - blk) {
case 1: exp_strategy[blk] = EXP_D45; break;
case 2:
case 3: exp_strategy[blk] = EXP_D25; break;
default: exp_strategy[blk] = EXP_D15; break;
}
blk = blk1;
}
}
/**
* Calculate exponent strategies for all channels.
* Array arrangement is reversed to simplify the per-channel calculation.
*/
static void compute_exp_strategy(AC3EncodeContext *s)
{
uint8_t *exp1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
uint8_t exp_str1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
int ch, blk;
for (ch = 0; ch < s->fbw_channels; ch++) {
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
exp1[ch][blk] = s->blocks[blk].exp[ch];
exp_str1[ch][blk] = s->blocks[blk].exp_strategy[ch];
}
compute_exp_strategy_ch(s, exp_str1[ch], exp1[ch]);
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
s->blocks[blk].exp_strategy[ch] = exp_str1[ch][blk];
}
if (s->lfe_on) {
ch = s->lfe_channel;
s->blocks[0].exp_strategy[ch] = EXP_D15;
for (blk = 1; blk < AC3_MAX_BLOCKS; blk++)
s->blocks[blk].exp_strategy[ch] = EXP_REUSE;
}
}
/**
* Set each encoded exponent in a block to the minimum of itself and the
* exponent in the same frequency bin of a following block.
* exp[i] = min(exp[i], exp1[i]
*/
static void exponent_min(uint8_t *exp, uint8_t *exp1, 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.
*/
static void encode_exponents_blk_ch(uint8_t *exp,
int nb_exps, int exp_strategy)
{
int nb_groups, i, k;
nb_groups = exponent_group_tab[exp_strategy-1][nb_exps] * 3;
/* for each group, compute the minimum exponent */
switch(exp_strategy) {
case EXP_D25:
for (i = 1, k = 1; i <= nb_groups; i++) {
uint8_t exp_min = exp[k];
if (exp[k+1] < exp_min)
exp_min = exp[k+1];
exp[i] = exp_min;
k += 2;
}
break;
case EXP_D45:
for (i = 1, k = 1; i <= nb_groups; i++) {
uint8_t exp_min = exp[k];
if (exp[k+1] < exp_min)
exp_min = exp[k+1];
if (exp[k+2] < exp_min)
exp_min = exp[k+2];
if (exp[k+3] < exp_min)
exp_min = exp[k+3];
exp[i] = exp_min;
k += 4;
}
break;
}
/* constraint for DC exponent */
if (exp[0] > 15)
exp[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++)
exp[i] = FFMIN(exp[i], exp[i-1] + 2);
i--;
while (--i >= 0)
exp[i] = FFMIN(exp[i], exp[i+1] + 2);
/* now we have the exponent values the decoder will see */
switch (exp_strategy) {
case EXP_D25:
for (i = nb_groups, k = nb_groups * 2; i > 0; i--) {
uint8_t exp1 = exp[i];
exp[k--] = exp1;
exp[k--] = exp1;
}
break;
case EXP_D45:
for (i = nb_groups, k = nb_groups * 4; i > 0; i--) {
exp[k] = exp[k-1] = exp[k-2] = exp[k-3] = exp[i];
k -= 4;
}
break;
}
}
/**
* Encode exponents from original extracted form to what the decoder will see.
* This copies and groups exponents based on exponent strategy and reduces
* deltas between adjacent exponent groups so that they can be differentially
* encoded.
*/
static void encode_exponents(AC3EncodeContext *s)
{
int blk, blk1, blk2, ch;
AC3Block *block, *block1, *block2;
for (ch = 0; ch < s->channels; ch++) {
blk = 0;
block = &s->blocks[0];
while (blk < AC3_MAX_BLOCKS) {
blk1 = blk + 1;
block1 = block + 1;
/* for the EXP_REUSE case we select the min of the exponents */
while (blk1 < AC3_MAX_BLOCKS && block1->exp_strategy[ch] == EXP_REUSE) {
exponent_min(block->exp[ch], block1->exp[ch], s->nb_coefs[ch]);
blk1++;
block1++;
}
encode_exponents_blk_ch(block->exp[ch], s->nb_coefs[ch],
block->exp_strategy[ch]);
/* copy encoded exponents for reuse case */
block2 = block + 1;
for (blk2 = blk+1; blk2 < blk1; blk2++, block2++) {
memcpy(block2->exp[ch], block->exp[ch],
s->nb_coefs[ch] * sizeof(uint8_t));
}
blk = blk1;
block = block1;
}
}
}
/**
* Group exponents.
* 3 delta-encoded exponents are in each 7-bit group. The number of groups
* varies depending on exponent strategy and bandwidth.
*/
static void group_exponents(AC3EncodeContext *s)
{
int blk, ch, i;
int group_size, nb_groups, bit_count;
uint8_t *p;
int delta0, delta1, delta2;
int exp0, exp1;
bit_count = 0;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
for (ch = 0; ch < s->channels; ch++) {
if (block->exp_strategy[ch] == EXP_REUSE) {
continue;
}
group_size = block->exp_strategy[ch] + (block->exp_strategy[ch] == EXP_D45);
nb_groups = exponent_group_tab[block->exp_strategy[ch]-1][s->nb_coefs[ch]];
bit_count += 4 + (nb_groups * 7);
p = block->exp[ch];
/* DC exponent */
exp1 = *p++;
block->grouped_exp[ch][0] = exp1;
/* remaining exponents are delta encoded */
for (i = 1; 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;
block->grouped_exp[ch][i] = ((delta0 * 5 + delta1) * 5) + delta2;
}
}
}
s->exponent_bits = bit_count;
}
/**
* Calculate final exponents from the supplied MDCT coefficients and exponent shift.
* Extract exponents from MDCT coefficients, calculate exponent strategies,
* and encode final exponents.
*/
static void process_exponents(AC3EncodeContext *s)
{
extract_exponents(s);
compute_exp_strategy(s);
encode_exponents(s);
group_exponents(s);
}
/**
* Count frame bits that are based solely on fixed parameters.
* This only has to be run once when the encoder is initialized.
*/
static void count_frame_bits_fixed(AC3EncodeContext *s)
{
static const int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };
int blk;
int frame_bits;
/* assumptions:
* no dynamic range codes
* no channel coupling
* no rematrixing
* bit allocation parameters do not change between blocks
* SNR offsets do not change between blocks
* no delta bit allocation
* no skipped data
* no auxilliary data
*/
/* header size */
frame_bits = 65;
frame_bits += frame_bits_inc[s->channel_mode];
/* audio blocks */
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
frame_bits += s->fbw_channels * 2 + 2; /* blksw * c, dithflag * c, dynrnge, cplstre */
if (s->channel_mode == AC3_CHMODE_STEREO) {
frame_bits++; /* rematstr */
if (!blk)
frame_bits += 4;
}
frame_bits += 2 * s->fbw_channels; /* chexpstr[2] * c */
if (s->lfe_on)
frame_bits++; /* lfeexpstr */
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->channels * (4 + 3);
/* auxdatae, crcrsv */
frame_bits += 2;
/* CRC */
frame_bits += 16;
s->frame_bits_fixed = frame_bits;
}
/**
* Initialize bit allocation.
* Set default parameter codes and calculate parameter values.
*/
static void bit_alloc_init(AC3EncodeContext *s)
{
int ch;
/* init default parameters */
s->slow_decay_code = 2;
s->fast_decay_code = 1;
s->slow_gain_code = 1;
s->db_per_bit_code = 3;
s->floor_code = 4;
for (ch = 0; ch < s->channels; ch++)
s->fast_gain_code[ch] = 4;
/* initial snr offset */
s->coarse_snr_offset = 40;
/* compute real values */
/* currently none of these values change during encoding, so we can just
set them once at initialization */
s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->bit_alloc.sr_shift;
s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->bit_alloc.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];
count_frame_bits_fixed(s);
}
/**
* Count the bits used to encode the frame, minus exponents and mantissas.
* Bits based on fixed parameters have already been counted, so now we just
* have to add the bits based on parameters that change during encoding.
*/
static void count_frame_bits(AC3EncodeContext *s)
{
int blk, ch;
int frame_bits = 0;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
uint8_t *exp_strategy = s->blocks[blk].exp_strategy;
for (ch = 0; ch < s->fbw_channels; ch++) {
if (exp_strategy[ch] != EXP_REUSE)
frame_bits += 6 + 2; /* chbwcod[6], gainrng[2] */
}
}
s->frame_bits = s->frame_bits_fixed + frame_bits;
}
/**
* Calculate the number of bits needed to encode a set of mantissas.
*/
static int compute_mantissa_size(int mant_cnt[5], uint8_t *bap, int nb_coefs)
{
int bits, b, i;
bits = 0;
for (i = 0; i < nb_coefs; i++) {
b = bap[i];
if (b <= 4) {
// bap=1 to bap=4 will be counted in compute_mantissa_size_final
mant_cnt[b]++;
} else if (b <= 13) {
// bap=5 to bap=13 use (bap-1) bits
bits += b - 1;
} else {
// bap=14 uses 14 bits and bap=15 uses 16 bits
bits += (b == 14) ? 14 : 16;
}
}
return bits;
}
/**
* Finalize the mantissa bit count by adding in the grouped mantissas.
*/
static int compute_mantissa_size_final(int mant_cnt[5])
{
// bap=1 : 3 mantissas in 5 bits
int bits = (mant_cnt[1] / 3) * 5;
// bap=2 : 3 mantissas in 7 bits
// bap=4 : 2 mantissas in 7 bits
bits += ((mant_cnt[2] / 3) + (mant_cnt[4] >> 1)) * 7;
// bap=3 : each mantissa is 3 bits
bits += mant_cnt[3] * 3;
return bits;
}
/**
* Calculate masking curve based on the final exponents.
* Also calculate the power spectral densities to use in future calculations.
*/
static void bit_alloc_masking(AC3EncodeContext *s)
{
int blk, ch;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
for (ch = 0; ch < s->channels; ch++) {
/* We only need psd and mask for calculating bap.
Since we currently do not calculate bap when exponent
strategy is EXP_REUSE we do not need to calculate psd or mask. */
if (block->exp_strategy[ch] != EXP_REUSE) {
ff_ac3_bit_alloc_calc_psd(block->exp[ch], 0,
s->nb_coefs[ch],
block->psd[ch], block->band_psd[ch]);
ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, block->band_psd[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,
block->mask[ch]);
}
}
}
}
/**
* Ensure that bap for each block and channel point to the current bap_buffer.
* They may have been switched during the bit allocation search.
*/
static void reset_block_bap(AC3EncodeContext *s)
{
int blk, ch;
if (s->blocks[0].bap[0] == s->bap_buffer)
return;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
for (ch = 0; ch < s->channels; ch++) {
s->blocks[blk].bap[ch] = &s->bap_buffer[AC3_MAX_COEFS * (blk * s->channels + ch)];
}
}
}
/**
* Run the bit allocation with a given SNR offset.
* This calculates the bit allocation pointers that will be used to determine
* the quantization of each mantissa.
* @return the number of bits needed for mantissas if the given SNR offset is
* is used.
*/
static int bit_alloc(AC3EncodeContext *s,
int snr_offset)
{
int blk, ch;
int mantissa_bits;
int mant_cnt[5];
snr_offset = (snr_offset - 240) << 2;
reset_block_bap(s);
mantissa_bits = 0;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
// initialize grouped mantissa counts. these are set so that they are
// padded to the next whole group size when bits are counted in
// compute_mantissa_size_final
mant_cnt[0] = mant_cnt[3] = 0;
mant_cnt[1] = mant_cnt[2] = 2;
mant_cnt[4] = 1;
for (ch = 0; ch < s->channels; ch++) {
/* Currently the only bit allocation parameters which vary across
blocks within a frame are the exponent values. We can take
advantage of that by reusing the bit allocation pointers
whenever we reuse exponents. */
if (block->exp_strategy[ch] == EXP_REUSE) {
memcpy(block->bap[ch], s->blocks[blk-1].bap[ch], AC3_MAX_COEFS);
} else {
ff_ac3_bit_alloc_calc_bap(block->mask[ch], block->psd[ch], 0,
s->nb_coefs[ch], snr_offset,
s->bit_alloc.floor, ff_ac3_bap_tab,
block->bap[ch]);
}
mantissa_bits += compute_mantissa_size(mant_cnt, block->bap[ch], s->nb_coefs[ch]);
}
mantissa_bits += compute_mantissa_size_final(mant_cnt);
}
return mantissa_bits;
}
/**
* Constant bitrate bit allocation search.
* Find the largest SNR offset that will allow data to fit in the frame.
*/
static int cbr_bit_allocation(AC3EncodeContext *s)
{
int ch;
int bits_left;
int snr_offset, snr_incr;
bits_left = 8 * s->frame_size - (s->frame_bits + s->exponent_bits);
snr_offset = s->coarse_snr_offset << 4;
while (snr_offset >= 0 &&
bit_alloc(s, snr_offset) > bits_left) {
snr_offset -= 64;
}
if (snr_offset < 0)
return AVERROR(EINVAL);
FFSWAP(uint8_t *, s->bap_buffer, s->bap1_buffer);
for (snr_incr = 64; snr_incr > 0; snr_incr >>= 2) {
while (snr_offset + 64 <= 1023 &&
bit_alloc(s, snr_offset + snr_incr) <= bits_left) {
snr_offset += snr_incr;
FFSWAP(uint8_t *, s->bap_buffer, s->bap1_buffer);
}
}
FFSWAP(uint8_t *, s->bap_buffer, s->bap1_buffer);
reset_block_bap(s);
s->coarse_snr_offset = snr_offset >> 4;
for (ch = 0; ch < s->channels; ch++)
s->fine_snr_offset[ch] = snr_offset & 0xF;
return 0;
}
/**
* Downgrade exponent strategies to reduce the bits used by the exponents.
* This is a fallback for when bit allocation fails with the normal exponent
* strategies. Each time this function is run it only downgrades the
* strategy in 1 channel of 1 block.
* @return non-zero if downgrade was unsuccessful
*/
static int downgrade_exponents(AC3EncodeContext *s)
{
int ch, blk;
for (ch = 0; ch < s->fbw_channels; ch++) {
for (blk = AC3_MAX_BLOCKS-1; blk >= 0; blk--) {
if (s->blocks[blk].exp_strategy[ch] == EXP_D15) {
s->blocks[blk].exp_strategy[ch] = EXP_D25;
return 0;
}
}
}
for (ch = 0; ch < s->fbw_channels; ch++) {
for (blk = AC3_MAX_BLOCKS-1; blk >= 0; blk--) {
if (s->blocks[blk].exp_strategy[ch] == EXP_D25) {
s->blocks[blk].exp_strategy[ch] = EXP_D45;
return 0;
}
}
}
for (ch = 0; ch < s->fbw_channels; ch++) {
/* block 0 cannot reuse exponents, so only downgrade D45 to REUSE if
the block number > 0 */
for (blk = AC3_MAX_BLOCKS-1; blk > 0; blk--) {
if (s->blocks[blk].exp_strategy[ch] > EXP_REUSE) {
s->blocks[blk].exp_strategy[ch] = EXP_REUSE;
return 0;
}
}
}
return -1;
}
/**
* Reduce the bandwidth to reduce the number of bits used for a given SNR offset.
* This is a second fallback for when bit allocation still fails after exponents
* have been downgraded.
* @return non-zero if bandwidth reduction was unsuccessful
*/
static int reduce_bandwidth(AC3EncodeContext *s, int min_bw_code)
{
int ch;
if (s->bandwidth_code[0] > min_bw_code) {
for (ch = 0; ch < s->fbw_channels; ch++) {
s->bandwidth_code[ch]--;
s->nb_coefs[ch] = s->bandwidth_code[ch] * 3 + 73;
}
return 0;
}
return -1;
}
/**
* Perform bit allocation search.
* Finds the SNR offset value that maximizes quality and fits in the specified
* frame size. Output is the SNR offset and a set of bit allocation pointers
* used to quantize the mantissas.
*/
static int compute_bit_allocation(AC3EncodeContext *s)
{
int ret;
count_frame_bits(s);
bit_alloc_masking(s);
ret = cbr_bit_allocation(s);
while (ret) {
/* fallback 1: downgrade exponents */
if (!downgrade_exponents(s)) {
extract_exponents(s);
encode_exponents(s);
group_exponents(s);
ret = compute_bit_allocation(s);
continue;
}
/* fallback 2: reduce bandwidth */
/* only do this if the user has not specified a specific cutoff
frequency */
if (!s->cutoff && !reduce_bandwidth(s, 0)) {
process_exponents(s);
ret = compute_bit_allocation(s);
continue;
}
/* fallbacks were not enough... */
break;
}
return ret;
}
/**
* Symmetric 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;
}
/**
* Asymmetric 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);
}
/**
* Quantize a set of mantissas for a single channel in a single block.
*/
static void quantize_mantissas_blk_ch(AC3EncodeContext *s,
int32_t *mdct_coef, int8_t exp_shift,
uint8_t *exp, uint8_t *bap,
uint16_t *qmant, int n)
{
int i;
for (i = 0; i < n; i++) {
int v;
int c = mdct_coef[i];
int e = exp[i] - exp_shift;
int b = bap[i];
switch (b) {
case 0:
v = 0;
break;
case 1:
v = sym_quant(c, e, 3);
switch (s->mant1_cnt) {
case 0:
s->qmant1_ptr = &qmant[i];
v = 9 * v;
s->mant1_cnt = 1;
break;
case 1:
*s->qmant1_ptr += 3 * v;
s->mant1_cnt = 2;
v = 128;
break;
default:
*s->qmant1_ptr += v;
s->mant1_cnt = 0;
v = 128;
break;
}
break;
case 2:
v = sym_quant(c, e, 5);
switch (s->mant2_cnt) {
case 0:
s->qmant2_ptr = &qmant[i];
v = 25 * v;
s->mant2_cnt = 1;
break;
case 1:
*s->qmant2_ptr += 5 * v;
s->mant2_cnt = 2;
v = 128;
break;
default:
*s->qmant2_ptr += v;
s->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 (s->mant4_cnt) {
case 0:
s->qmant4_ptr = &qmant[i];
v = 11 * v;
s->mant4_cnt = 1;
break;
default:
*s->qmant4_ptr += v;
s->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[i] = v;
}
}
/**
* Quantize mantissas using coefficients, exponents, and bit allocation pointers.
*/
static void quantize_mantissas(AC3EncodeContext *s)
{
int blk, ch;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
s->mant1_cnt = s->mant2_cnt = s->mant4_cnt = 0;
s->qmant1_ptr = s->qmant2_ptr = s->qmant4_ptr = NULL;
for (ch = 0; ch < s->channels; ch++) {
quantize_mantissas_blk_ch(s, block->mdct_coef[ch], block->exp_shift[ch],
block->exp[ch], block->bap[ch],
block->qmant[ch], s->nb_coefs[ch]);
}
}
}
/**
* Write the AC-3 frame header to the output bitstream.
*/
static void output_frame_header(AC3EncodeContext *s)
{
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->bit_alloc.sr_code);
put_bits(&s->pb, 6, s->frame_size_code + (s->frame_size - s->frame_size_min) / 2);
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_on); /* 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 */
}
/**
* Write one audio block to the output bitstream.
*/
static void output_audio_block(AC3EncodeContext *s,
int block_num)
{
int ch, i, baie, rbnd;
AC3Block *block = &s->blocks[block_num];
/* block switching */
for (ch = 0; ch < s->fbw_channels; ch++)
put_bits(&s->pb, 1, 0);
/* dither flags */
for (ch = 0; ch < s->fbw_channels; ch++)
put_bits(&s->pb, 1, 1);
/* dynamic range codes */
put_bits(&s->pb, 1, 0);
/* channel coupling */
if (!block_num) {
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 */
}
/* stereo rematrixing */
if (s->channel_mode == AC3_CHMODE_STEREO) {
if (!block_num) {
/* 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);
}
}
/* exponent strategy */
for (ch = 0; ch < s->fbw_channels; ch++)
put_bits(&s->pb, 2, block->exp_strategy[ch]);
if (s->lfe_on)
put_bits(&s->pb, 1, block->exp_strategy[s->lfe_channel]);
/* bandwidth */
for (ch = 0; ch < s->fbw_channels; ch++) {
if (block->exp_strategy[ch] != EXP_REUSE)
put_bits(&s->pb, 6, s->bandwidth_code[ch]);
}
/* exponents */
for (ch = 0; ch < s->channels; ch++) {
int nb_groups;
if (block->exp_strategy[ch] == EXP_REUSE)
continue;
/* DC exponent */
put_bits(&s->pb, 4, block->grouped_exp[ch][0]);
/* exponent groups */
nb_groups = exponent_group_tab[block->exp_strategy[ch]-1][s->nb_coefs[ch]];
for (i = 1; i <= nb_groups; i++)
put_bits(&s->pb, 7, block->grouped_exp[ch][i]);
/* gain range info */
if (ch != s->lfe_channel)
put_bits(&s->pb, 2, 0);
}
/* 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);
if (baie) {
put_bits(&s->pb, 6, s->coarse_snr_offset);
for (ch = 0; ch < s->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 */
/* mantissas */
for (ch = 0; ch < s->channels; ch++) {
int b, q;
for (i = 0; i < s->nb_coefs[ch]; i++) {
q = block->qmant[ch][i];
b = block->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;
}
}
}
}
/** CRC-16 Polynomial */
#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;
}
/**
* Fill the end of the frame with 0's and compute the two CRCs.
*/
static void output_frame_end(AC3EncodeContext *s)
{
const AVCRC *crc_ctx = av_crc_get_table(AV_CRC_16_ANSI);
int frame_size_58, pad_bytes, crc1, crc2_partial, crc2, crc_inv;
uint8_t *frame;
frame_size_58 = ((s->frame_size >> 2) + (s->frame_size >> 4)) << 1;
/* pad the remainder of the frame with zeros */
flush_put_bits(&s->pb);
frame = s->pb.buf;
pad_bytes = s->frame_size - (put_bits_ptr(&s->pb) - frame) - 2;
assert(pad_bytes >= 0);
if (pad_bytes > 0)
memset(put_bits_ptr(&s->pb), 0, pad_bytes);
/* compute crc1 */
/* this is not so easy because it is at the beginning of the data... */
crc1 = av_bswap16(av_crc(crc_ctx, 0, frame + 4, frame_size_58 - 4));
crc_inv = s->crc_inv[s->frame_size > s->frame_size_min];
crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);
AV_WB16(frame + 2, crc1);
/* compute crc2 */
crc2_partial = av_crc(crc_ctx, 0, frame + frame_size_58,
s->frame_size - frame_size_58 - 3);
crc2 = av_crc(crc_ctx, crc2_partial, frame + s->frame_size - 3, 1);
/* ensure crc2 does not match sync word by flipping crcrsv bit if needed */
if (crc2 == 0x770B) {
frame[s->frame_size - 3] ^= 0x1;
crc2 = av_crc(crc_ctx, crc2_partial, frame + s->frame_size - 3, 1);
}
crc2 = av_bswap16(crc2);
AV_WB16(frame + s->frame_size - 2, crc2);
}
/**
* Write the frame to the output bitstream.
*/
static void output_frame(AC3EncodeContext *s,
unsigned char *frame)
{
int blk;
init_put_bits(&s->pb, frame, AC3_MAX_CODED_FRAME_SIZE);
output_frame_header(s);
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
output_audio_block(s, blk);
output_frame_end(s);
}
/**
* Encode a single AC-3 frame.
*/
static int ac3_encode_frame(AVCodecContext *avctx,
unsigned char *frame, int buf_size, void *data)
{
AC3EncodeContext *s = avctx->priv_data;
const int16_t *samples = data;
int ret;
if (s->bit_alloc.sr_code == 1)
adjust_frame_size(s);
deinterleave_input_samples(s, samples);
apply_mdct(s);
process_exponents(s);
ret = compute_bit_allocation(s);
if (ret) {
av_log(avctx, AV_LOG_ERROR, "Bit allocation failed. Try increasing the bitrate.\n");
return ret;
}
quantize_mantissas(s);
output_frame(s, frame);
return s->frame_size;
}
/**
* Finalize encoding and free any memory allocated by the encoder.
*/
static av_cold int ac3_encode_close(AVCodecContext *avctx)
{
int blk, ch;
AC3EncodeContext *s = avctx->priv_data;
for (ch = 0; ch < s->channels; ch++)
av_freep(&s->planar_samples[ch]);
av_freep(&s->planar_samples);
av_freep(&s->bap_buffer);
av_freep(&s->bap1_buffer);
av_freep(&s->mdct_coef_buffer);
av_freep(&s->exp_buffer);
av_freep(&s->grouped_exp_buffer);
av_freep(&s->psd_buffer);
av_freep(&s->band_psd_buffer);
av_freep(&s->mask_buffer);
av_freep(&s->qmant_buffer);
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
av_freep(&block->bap);
av_freep(&block->mdct_coef);
av_freep(&block->exp);
av_freep(&block->grouped_exp);
av_freep(&block->psd);
av_freep(&block->band_psd);
av_freep(&block->mask);
av_freep(&block->qmant);
}
mdct_end(&s->mdct);
av_freep(&avctx->coded_frame);
return 0;
}
/**
* Set channel information during initialization.
*/
static av_cold int set_channel_info(AC3EncodeContext *s, int channels,
int64_t *channel_layout)
{
int ch_layout;
if (channels < 1 || channels > AC3_MAX_CHANNELS)
return AVERROR(EINVAL);
if ((uint64_t)*channel_layout > 0x7FF)
return AVERROR(EINVAL);
ch_layout = *channel_layout;
if (!ch_layout)
ch_layout = avcodec_guess_channel_layout(channels, CODEC_ID_AC3, NULL);
if (av_get_channel_layout_nb_channels(ch_layout) != channels)
return AVERROR(EINVAL);
s->lfe_on = !!(ch_layout & AV_CH_LOW_FREQUENCY);
s->channels = channels;
s->fbw_channels = channels - s->lfe_on;
s->lfe_channel = s->lfe_on ? s->fbw_channels : -1;
if (s->lfe_on)
ch_layout -= AV_CH_LOW_FREQUENCY;
switch (ch_layout) {
case AV_CH_LAYOUT_MONO: s->channel_mode = AC3_CHMODE_MONO; break;
case AV_CH_LAYOUT_STEREO: s->channel_mode = AC3_CHMODE_STEREO; break;
case AV_CH_LAYOUT_SURROUND: s->channel_mode = AC3_CHMODE_3F; break;
case AV_CH_LAYOUT_2_1: s->channel_mode = AC3_CHMODE_2F1R; break;
case AV_CH_LAYOUT_4POINT0: s->channel_mode = AC3_CHMODE_3F1R; break;
case AV_CH_LAYOUT_QUAD:
case AV_CH_LAYOUT_2_2: s->channel_mode = AC3_CHMODE_2F2R; break;
case AV_CH_LAYOUT_5POINT0:
case AV_CH_LAYOUT_5POINT0_BACK: s->channel_mode = AC3_CHMODE_3F2R; break;
default:
return AVERROR(EINVAL);
}
s->channel_map = ff_ac3_enc_channel_map[s->channel_mode][s->lfe_on];
*channel_layout = ch_layout;
if (s->lfe_on)
*channel_layout |= AV_CH_LOW_FREQUENCY;
return 0;
}
static av_cold int validate_options(AVCodecContext *avctx, AC3EncodeContext *s)
{
int i, ret;
/* validate channel layout */
if (!avctx->channel_layout) {
av_log(avctx, AV_LOG_WARNING, "No channel layout specified. The "
"encoder will guess the layout, but it "
"might be incorrect.\n");
}
ret = set_channel_info(s, avctx->channels, &avctx->channel_layout);
if (ret) {
av_log(avctx, AV_LOG_ERROR, "invalid channel layout\n");
return ret;
}
/* validate sample rate */
for (i = 0; i < 9; i++) {
if ((ff_ac3_sample_rate_tab[i / 3] >> (i % 3)) == avctx->sample_rate)
break;
}
if (i == 9) {
av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
return AVERROR(EINVAL);
}
s->sample_rate = avctx->sample_rate;
s->bit_alloc.sr_shift = i % 3;
s->bit_alloc.sr_code = i / 3;
/* validate bit rate */
for (i = 0; i < 19; i++) {
if ((ff_ac3_bitrate_tab[i] >> s->bit_alloc.sr_shift)*1000 == avctx->bit_rate)
break;
}
if (i == 19) {
av_log(avctx, AV_LOG_ERROR, "invalid bit rate\n");
return AVERROR(EINVAL);
}
s->bit_rate = avctx->bit_rate;
s->frame_size_code = i << 1;
/* validate cutoff */
if (avctx->cutoff < 0) {
av_log(avctx, AV_LOG_ERROR, "invalid cutoff frequency\n");
return AVERROR(EINVAL);
}
s->cutoff = avctx->cutoff;
if (s->cutoff > (s->sample_rate >> 1))
s->cutoff = s->sample_rate >> 1;
return 0;
}
/**
* Set bandwidth for all channels.
* The user can optionally supply a cutoff frequency. Otherwise an appropriate
* default value will be used.
*/
static av_cold void set_bandwidth(AC3EncodeContext *s)
{
int ch, bw_code;
if (s->cutoff) {
/* calculate bandwidth based on user-specified cutoff frequency */
int fbw_coeffs;
fbw_coeffs = s->cutoff * 2 * AC3_MAX_COEFS / 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;
}
/* set number of coefficients for each channel */
for (ch = 0; ch < s->fbw_channels; ch++) {
s->bandwidth_code[ch] = bw_code;
s->nb_coefs[ch] = bw_code * 3 + 73;
}
if (s->lfe_on)
s->nb_coefs[s->lfe_channel] = 7; /* LFE channel always has 7 coefs */
}
static av_cold int allocate_buffers(AVCodecContext *avctx)
{
int blk, ch;
AC3EncodeContext *s = avctx->priv_data;
FF_ALLOC_OR_GOTO(avctx, s->planar_samples, s->channels * sizeof(*s->planar_samples),
alloc_fail);
for (ch = 0; ch < s->channels; ch++) {
FF_ALLOCZ_OR_GOTO(avctx, s->planar_samples[ch],
(AC3_FRAME_SIZE+AC3_BLOCK_SIZE) * sizeof(**s->planar_samples),
alloc_fail);
}
FF_ALLOC_OR_GOTO(avctx, s->bap_buffer, AC3_MAX_BLOCKS * s->channels *
AC3_MAX_COEFS * sizeof(*s->bap_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->bap1_buffer, AC3_MAX_BLOCKS * s->channels *
AC3_MAX_COEFS * sizeof(*s->bap1_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->mdct_coef_buffer, AC3_MAX_BLOCKS * s->channels *
AC3_MAX_COEFS * sizeof(*s->mdct_coef_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->exp_buffer, AC3_MAX_BLOCKS * s->channels *
AC3_MAX_COEFS * sizeof(*s->exp_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->grouped_exp_buffer, AC3_MAX_BLOCKS * s->channels *
128 * sizeof(*s->grouped_exp_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->psd_buffer, AC3_MAX_BLOCKS * s->channels *
AC3_MAX_COEFS * sizeof(*s->psd_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->band_psd_buffer, AC3_MAX_BLOCKS * s->channels *
64 * sizeof(*s->band_psd_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->mask_buffer, AC3_MAX_BLOCKS * s->channels *
64 * sizeof(*s->mask_buffer), alloc_fail);
FF_ALLOC_OR_GOTO(avctx, s->qmant_buffer, AC3_MAX_BLOCKS * s->channels *
AC3_MAX_COEFS * sizeof(*s->qmant_buffer), alloc_fail);
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
FF_ALLOC_OR_GOTO(avctx, block->bap, s->channels * sizeof(*block->bap),
alloc_fail);
FF_ALLOCZ_OR_GOTO(avctx, block->mdct_coef, s->channels * sizeof(*block->mdct_coef),
alloc_fail);
FF_ALLOCZ_OR_GOTO(avctx, block->exp, s->channels * sizeof(*block->exp),
alloc_fail);
FF_ALLOCZ_OR_GOTO(avctx, block->grouped_exp, s->channels * sizeof(*block->grouped_exp),
alloc_fail);
FF_ALLOCZ_OR_GOTO(avctx, block->psd, s->channels * sizeof(*block->psd),
alloc_fail);
FF_ALLOCZ_OR_GOTO(avctx, block->band_psd, s->channels * sizeof(*block->band_psd),
alloc_fail);
FF_ALLOCZ_OR_GOTO(avctx, block->mask, s->channels * sizeof(*block->mask),
alloc_fail);
FF_ALLOCZ_OR_GOTO(avctx, block->qmant, s->channels * sizeof(*block->qmant),
alloc_fail);
for (ch = 0; ch < s->channels; ch++) {
block->bap[ch] = &s->bap_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
block->mdct_coef[ch] = &s->mdct_coef_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
block->exp[ch] = &s->exp_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
block->grouped_exp[ch] = &s->grouped_exp_buffer[128 * (blk * s->channels + ch)];
block->psd[ch] = &s->psd_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
block->band_psd[ch] = &s->band_psd_buffer [64 * (blk * s->channels + ch)];
block->mask[ch] = &s->mask_buffer [64 * (blk * s->channels + ch)];
block->qmant[ch] = &s->qmant_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
}
}
return 0;
alloc_fail:
return AVERROR(ENOMEM);
}
/**
* Initialize the encoder.
*/
static av_cold int ac3_encode_init(AVCodecContext *avctx)
{
AC3EncodeContext *s = avctx->priv_data;
int ret, frame_size_58;
avctx->frame_size = AC3_FRAME_SIZE;
ac3_common_init();
ret = validate_options(avctx, s);
if (ret)
return ret;
s->bitstream_id = 8 + s->bit_alloc.sr_shift;
s->bitstream_mode = 0; /* complete main audio service */
s->frame_size_min = 2 * ff_ac3_frame_size_tab[s->frame_size_code][s->bit_alloc.sr_code];
s->bits_written = 0;
s->samples_written = 0;
s->frame_size = s->frame_size_min;
/* calculate crc_inv for both possible frame sizes */
frame_size_58 = (( s->frame_size >> 2) + ( s->frame_size >> 4)) << 1;
s->crc_inv[0] = pow_poly((CRC16_POLY >> 1), (8 * frame_size_58) - 16, CRC16_POLY);
if (s->bit_alloc.sr_code == 1) {
frame_size_58 = (((s->frame_size+2) >> 2) + ((s->frame_size+2) >> 4)) << 1;
s->crc_inv[1] = pow_poly((CRC16_POLY >> 1), (8 * frame_size_58) - 16, CRC16_POLY);
}
set_bandwidth(s);
exponent_init(s);
bit_alloc_init(s);
ret = mdct_init(avctx, &s->mdct, 9);
if (ret)
goto init_fail;
ret = allocate_buffers(avctx);
if (ret)
goto init_fail;
avctx->coded_frame= avcodec_alloc_frame();
dsputil_init(&s->dsp, avctx);
return 0;
init_fail:
ac3_encode_close(avctx);
return ret;
}
#ifdef TEST
/*************************************************************************/
/* TEST */
#include "libavutil/lfg.h"
#define MDCT_NBITS 9
#define MDCT_SAMPLES (1 << MDCT_NBITS)
#define FN (MDCT_SAMPLES/4)
static void fft_test(AC3MDCTContext *mdct, AVLFG *lfg)
{
IComplex in[FN], in1[FN];
int k, n, i;
float sum_re, sum_im, a;
for (i = 0; i < FN; i++) {
in[i].re = av_lfg_get(lfg) % 65535 - 32767;
in[i].im = av_lfg_get(lfg) % 65535 - 32767;
in1[i] = in[i];
}
fft(mdct, 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);
}
av_log(NULL, AV_LOG_DEBUG, "%3d: %6d,%6d %6.0f,%6.0f\n",
k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);
}
}
static void mdct_test(AC3MDCTContext *mdct, AVLFG *lfg)
{
int16_t input[MDCT_SAMPLES];
int32_t output[AC3_MAX_COEFS];
float input1[MDCT_SAMPLES];
float output1[AC3_MAX_COEFS];
float s, a, err, e, emax;
int i, k, n;
for (i = 0; i < MDCT_SAMPLES; i++) {
input[i] = (av_lfg_get(lfg) % 65535 - 32767) * 9 / 10;
input1[i] = input[i];
}
mdct512(mdct, output, input);
/* do it by hand */
for (k = 0; k < AC3_MAX_COEFS; k++) {
s = 0;
for (n = 0; n < MDCT_SAMPLES; n++) {
a = (2*M_PI*(2*n+1+MDCT_SAMPLES/2)*(2*k+1) / (4 * MDCT_SAMPLES));
s += input1[n] * cos(a);
}
output1[k] = -2 * s / MDCT_SAMPLES;
}
err = 0;
emax = 0;
for (i = 0; i < AC3_MAX_COEFS; i++) {
av_log(NULL, AV_LOG_DEBUG, "%3d: %7d %7.0f\n", i, output[i], output1[i]);
e = output[i] - output1[i];
if (e > emax)
emax = e;
err += e * e;
}
av_log(NULL, AV_LOG_DEBUG, "err2=%f emax=%f\n", err / AC3_MAX_COEFS, emax);
}
int main(void)
{
AVLFG lfg;
AC3MDCTContext mdct;
mdct.avctx = NULL;
av_log_set_level(AV_LOG_DEBUG);
mdct_init(&mdct, 9);
fft_test(&mdct, &lfg);
mdct_test(&mdct, &lfg);
return 0;
}
#endif /* TEST */
AVCodec ac3_encoder = {
"ac3",
AVMEDIA_TYPE_AUDIO,
CODEC_ID_AC3,
sizeof(AC3EncodeContext),
ac3_encode_init,
ac3_encode_frame,
ac3_encode_close,
NULL,
.sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
.long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
.channel_layouts = (const int64_t[]){
AV_CH_LAYOUT_MONO,
AV_CH_LAYOUT_STEREO,
AV_CH_LAYOUT_2_1,
AV_CH_LAYOUT_SURROUND,
AV_CH_LAYOUT_2_2,
AV_CH_LAYOUT_QUAD,
AV_CH_LAYOUT_4POINT0,
AV_CH_LAYOUT_5POINT0,
AV_CH_LAYOUT_5POINT0_BACK,
(AV_CH_LAYOUT_MONO | AV_CH_LOW_FREQUENCY),
(AV_CH_LAYOUT_STEREO | AV_CH_LOW_FREQUENCY),
(AV_CH_LAYOUT_2_1 | AV_CH_LOW_FREQUENCY),
(AV_CH_LAYOUT_SURROUND | AV_CH_LOW_FREQUENCY),
(AV_CH_LAYOUT_2_2 | AV_CH_LOW_FREQUENCY),
(AV_CH_LAYOUT_QUAD | AV_CH_LOW_FREQUENCY),
(AV_CH_LAYOUT_4POINT0 | AV_CH_LOW_FREQUENCY),
AV_CH_LAYOUT_5POINT1,
AV_CH_LAYOUT_5POINT1_BACK,
0 },
};
Reference in New Issue View Git Blame Copy Permalink