2 * The simplest AC-3 encoder
3 * Copyright (c) 2000 Fabrice Bellard
4 * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
5 * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
7 * This file is part of FFmpeg.
9 * FFmpeg is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
14 * FFmpeg is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with FFmpeg; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
26 * The simplest AC-3 encoder.
31 #include "libavcore/audioconvert.h"
32 #include "libavutil/crc.h"
37 #include "audioconvert.h"
40 /** Maximum number of exponent groups. +1 for separate DC exponent. */
41 #define AC3_MAX_EXP_GROUPS 85
43 /** Scale a float value by 2^bits and convert to an integer. */
44 #define SCALE_FLOAT(a, bits) lrintf((a) * (float)(1 << (bits)))
46 typedef int16_t SampleType;
47 typedef int32_t CoefType;
49 #define SCALE_COEF(a) (a)
51 /** Scale a float value by 2^15, convert to an integer, and clip to range -32767..32767. */
52 #define FIX15(a) av_clip(SCALE_FLOAT(a, 15), -32767, 32767)
57 * Used in fixed-point MDCT calculation.
59 typedef struct IComplex {
63 typedef struct AC3MDCTContext {
64 const int16_t *window; ///< MDCT window function
65 int nbits; ///< log2(transform size)
66 int16_t *costab; ///< FFT cos table
67 int16_t *sintab; ///< FFT sin table
68 int16_t *xcos1; ///< MDCT cos table
69 int16_t *xsin1; ///< MDCT sin table
70 int16_t *rot_tmp; ///< temp buffer for pre-rotated samples
71 IComplex *cplx_tmp; ///< temp buffer for complex pre-rotated samples
75 * Data for a single audio block.
77 typedef struct AC3Block {
78 uint8_t **bap; ///< bit allocation pointers (bap)
79 CoefType **mdct_coef; ///< MDCT coefficients
80 uint8_t **exp; ///< original exponents
81 uint8_t **grouped_exp; ///< grouped exponents
82 int16_t **psd; ///< psd per frequency bin
83 int16_t **band_psd; ///< psd per critical band
84 int16_t **mask; ///< masking curve
85 uint16_t **qmant; ///< quantized mantissas
86 uint8_t exp_strategy[AC3_MAX_CHANNELS]; ///< exponent strategies
87 int8_t exp_shift[AC3_MAX_CHANNELS]; ///< exponent shift values
91 * AC-3 encoder private context.
93 typedef struct AC3EncodeContext {
94 PutBitContext pb; ///< bitstream writer context
96 AC3MDCTContext mdct; ///< MDCT context
98 AC3Block blocks[AC3_MAX_BLOCKS]; ///< per-block info
100 int bitstream_id; ///< bitstream id (bsid)
101 int bitstream_mode; ///< bitstream mode (bsmod)
103 int bit_rate; ///< target bit rate, in bits-per-second
104 int sample_rate; ///< sampling frequency, in Hz
106 int frame_size_min; ///< minimum frame size in case rounding is necessary
107 int frame_size; ///< current frame size in bytes
108 int frame_size_code; ///< frame size code (frmsizecod)
110 int bits_written; ///< bit count (used to avg. bitrate)
111 int samples_written; ///< sample count (used to avg. bitrate)
113 int fbw_channels; ///< number of full-bandwidth channels (nfchans)
114 int channels; ///< total number of channels (nchans)
115 int lfe_on; ///< indicates if there is an LFE channel (lfeon)
116 int lfe_channel; ///< channel index of the LFE channel
117 int channel_mode; ///< channel mode (acmod)
118 const uint8_t *channel_map; ///< channel map used to reorder channels
120 int cutoff; ///< user-specified cutoff frequency, in Hz
121 int bandwidth_code[AC3_MAX_CHANNELS]; ///< bandwidth code (0 to 60) (chbwcod)
122 int nb_coefs[AC3_MAX_CHANNELS];
124 /* bitrate allocation control */
125 int slow_gain_code; ///< slow gain code (sgaincod)
126 int slow_decay_code; ///< slow decay code (sdcycod)
127 int fast_decay_code; ///< fast decay code (fdcycod)
128 int db_per_bit_code; ///< dB/bit code (dbpbcod)
129 int floor_code; ///< floor code (floorcod)
130 AC3BitAllocParameters bit_alloc; ///< bit allocation parameters
131 int coarse_snr_offset; ///< coarse SNR offsets (csnroffst)
132 int fast_gain_code[AC3_MAX_CHANNELS]; ///< fast gain codes (signal-to-mask ratio) (fgaincod)
133 int fine_snr_offset[AC3_MAX_CHANNELS]; ///< fine SNR offsets (fsnroffst)
134 int frame_bits_fixed; ///< number of non-coefficient bits for fixed parameters
135 int frame_bits; ///< all frame bits except exponents and mantissas
136 int exponent_bits; ///< number of bits used for exponents
138 /* mantissa encoding */
139 int mant1_cnt, mant2_cnt, mant4_cnt; ///< mantissa counts for bap=1,2,4
140 uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr; ///< mantissa pointers for bap=1,2,4
142 SampleType **planar_samples;
144 uint8_t *bap1_buffer;
145 CoefType *mdct_coef_buffer;
147 uint8_t *grouped_exp_buffer;
149 int16_t *band_psd_buffer;
150 int16_t *mask_buffer;
151 uint16_t *qmant_buffer;
153 DECLARE_ALIGNED(16, SampleType, windowed_samples)[AC3_WINDOW_SIZE];
158 * LUT for number of exponent groups.
159 * exponent_group_tab[exponent strategy-1][number of coefficients]
161 static uint8_t exponent_group_tab[3][256];
165 * List of supported channel layouts.
167 static const int64_t ac3_channel_layouts[] = {
171 AV_CH_LAYOUT_SURROUND,
174 AV_CH_LAYOUT_4POINT0,
175 AV_CH_LAYOUT_5POINT0,
176 AV_CH_LAYOUT_5POINT0_BACK,
177 (AV_CH_LAYOUT_MONO | AV_CH_LOW_FREQUENCY),
178 (AV_CH_LAYOUT_STEREO | AV_CH_LOW_FREQUENCY),
179 (AV_CH_LAYOUT_2_1 | AV_CH_LOW_FREQUENCY),
180 (AV_CH_LAYOUT_SURROUND | AV_CH_LOW_FREQUENCY),
181 (AV_CH_LAYOUT_2_2 | AV_CH_LOW_FREQUENCY),
182 (AV_CH_LAYOUT_QUAD | AV_CH_LOW_FREQUENCY),
183 (AV_CH_LAYOUT_4POINT0 | AV_CH_LOW_FREQUENCY),
184 AV_CH_LAYOUT_5POINT1,
185 AV_CH_LAYOUT_5POINT1_BACK,
191 * Adjust the frame size to make the average bit rate match the target bit rate.
192 * This is only needed for 11025, 22050, and 44100 sample rates.
194 static void adjust_frame_size(AC3EncodeContext *s)
196 while (s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {
197 s->bits_written -= s->bit_rate;
198 s->samples_written -= s->sample_rate;
200 s->frame_size = s->frame_size_min +
201 2 * (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
202 s->bits_written += s->frame_size * 8;
203 s->samples_written += AC3_FRAME_SIZE;
208 * Deinterleave input samples.
209 * Channels are reordered from FFmpeg's default order to AC-3 order.
211 static void deinterleave_input_samples(AC3EncodeContext *s,
212 const SampleType *samples)
216 /* deinterleave and remap input samples */
217 for (ch = 0; ch < s->channels; ch++) {
218 const SampleType *sptr;
221 /* copy last 256 samples of previous frame to the start of the current frame */
222 memcpy(&s->planar_samples[ch][0], &s->planar_samples[ch][AC3_FRAME_SIZE],
223 AC3_BLOCK_SIZE * sizeof(s->planar_samples[0][0]));
227 sptr = samples + s->channel_map[ch];
228 for (i = AC3_BLOCK_SIZE; i < AC3_FRAME_SIZE+AC3_BLOCK_SIZE; i++) {
229 s->planar_samples[ch][i] = *sptr;
237 * Finalize MDCT and free allocated memory.
239 static av_cold void mdct_end(AC3MDCTContext *mdct)
242 av_freep(&mdct->costab);
243 av_freep(&mdct->sintab);
244 av_freep(&mdct->xcos1);
245 av_freep(&mdct->xsin1);
246 av_freep(&mdct->rot_tmp);
247 av_freep(&mdct->cplx_tmp);
252 * Initialize FFT tables.
253 * @param ln log2(FFT size)
255 static av_cold int fft_init(AVCodecContext *avctx, AC3MDCTContext *mdct, int ln)
263 FF_ALLOC_OR_GOTO(avctx, mdct->costab, n2 * sizeof(*mdct->costab), fft_alloc_fail);
264 FF_ALLOC_OR_GOTO(avctx, mdct->sintab, n2 * sizeof(*mdct->sintab), fft_alloc_fail);
266 for (i = 0; i < n2; i++) {
267 alpha = 2.0 * M_PI * i / n;
268 mdct->costab[i] = FIX15(cos(alpha));
269 mdct->sintab[i] = FIX15(sin(alpha));
275 return AVERROR(ENOMEM);
280 * Initialize MDCT tables.
281 * @param nbits log2(MDCT size)
283 static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
293 ret = fft_init(avctx, mdct, nbits - 2);
297 mdct->window = ff_ac3_window;
299 FF_ALLOC_OR_GOTO(avctx, mdct->xcos1, n4 * sizeof(*mdct->xcos1), mdct_alloc_fail);
300 FF_ALLOC_OR_GOTO(avctx, mdct->xsin1, n4 * sizeof(*mdct->xsin1), mdct_alloc_fail);
301 FF_ALLOC_OR_GOTO(avctx, mdct->rot_tmp, n * sizeof(*mdct->rot_tmp), mdct_alloc_fail);
302 FF_ALLOC_OR_GOTO(avctx, mdct->cplx_tmp, n4 * sizeof(*mdct->cplx_tmp), mdct_alloc_fail);
304 for (i = 0; i < n4; i++) {
305 float alpha = 2.0 * M_PI * (i + 1.0 / 8.0) / n;
306 mdct->xcos1[i] = FIX15(-cos(alpha));
307 mdct->xsin1[i] = FIX15(-sin(alpha));
313 return AVERROR(ENOMEM);
318 #define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1) \
320 int ax, ay, bx, by; \
325 pre = (bx + ax) >> 1; \
326 pim = (by + ay) >> 1; \
327 qre = (bx - ax) >> 1; \
328 qim = (by - ay) >> 1; \
332 /** Complex multiply */
333 #define CMUL(pre, pim, are, aim, bre, bim) \
335 pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15; \
336 pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15; \
341 * Calculate a 2^n point complex FFT on 2^ln points.
342 * @param z complex input/output samples
343 * @param ln log2(FFT size)
345 static void fft(AC3MDCTContext *mdct, IComplex *z, int ln)
349 register IComplex *p,*q;
355 for (j = 0; j < np; j++) {
356 int k = av_reverse[j] >> (8 - ln);
358 FFSWAP(IComplex, z[k], z[j]);
366 BF(p[0].re, p[0].im, p[1].re, p[1].im,
367 p[0].re, p[0].im, p[1].re, p[1].im);
376 BF(p[0].re, p[0].im, p[2].re, p[2].im,
377 p[0].re, p[0].im, p[2].re, p[2].im);
378 BF(p[1].re, p[1].im, p[3].re, p[3].im,
379 p[1].re, p[1].im, p[3].im, -p[3].re);
391 for (j = 0; j < nblocks; j++) {
392 BF(p->re, p->im, q->re, q->im,
393 p->re, p->im, q->re, q->im);
396 for(l = nblocks; l < np2; l += nblocks) {
397 CMUL(tmp_re, tmp_im, mdct->costab[l], -mdct->sintab[l], q->re, q->im);
398 BF(p->re, p->im, q->re, q->im,
399 p->re, p->im, tmp_re, tmp_im);
406 nblocks = nblocks >> 1;
407 nloops = nloops << 1;
413 * Calculate a 512-point MDCT
414 * @param out 256 output frequency coefficients
415 * @param in 512 windowed input audio samples
417 static void mdct512(AC3MDCTContext *mdct, int32_t *out, int16_t *in)
419 int i, re, im, n, n2, n4;
420 int16_t *rot = mdct->rot_tmp;
421 IComplex *x = mdct->cplx_tmp;
423 n = 1 << mdct->nbits;
427 /* shift to simplify computations */
428 for (i = 0; i <n4; i++)
429 rot[i] = -in[i + 3*n4];
430 memcpy(&rot[n4], &in[0], 3*n4*sizeof(*in));
433 for (i = 0; i < n4; i++) {
434 re = ((int)rot[ 2*i] - (int)rot[ n-1-2*i]) >> 1;
435 im = -((int)rot[n2+2*i] - (int)rot[n2-1-2*i]) >> 1;
436 CMUL(x[i].re, x[i].im, re, im, -mdct->xcos1[i], mdct->xsin1[i]);
439 fft(mdct, x, mdct->nbits - 2);
442 for (i = 0; i < n4; i++) {
445 CMUL(out[n2-1-2*i], out[2*i], re, im, mdct->xsin1[i], mdct->xcos1[i]);
451 * Apply KBD window to input samples prior to MDCT.
453 static void apply_window(int16_t *output, const int16_t *input,
454 const int16_t *window, int n)
459 for (i = 0; i < n2; i++) {
460 output[i] = MUL16(input[i], window[i]) >> 15;
461 output[n-i-1] = MUL16(input[n-i-1], window[i]) >> 15;
467 * Calculate the log2() of the maximum absolute value in an array.
468 * @param tab input array
469 * @param n number of values in the array
470 * @return log2(max(abs(tab[])))
472 static int log2_tab(int16_t *tab, int n)
477 for (i = 0; i < n; i++)
485 * Left-shift each value in an array by a specified amount.
486 * @param tab input array
487 * @param n number of values in the array
488 * @param lshift left shift amount. a negative value means right shift.
490 static void lshift_tab(int16_t *tab, int n, int lshift)
495 for (i = 0; i < n; i++)
497 } else if (lshift < 0) {
499 for (i = 0; i < n; i++)
506 * Normalize the input samples to use the maximum available precision.
507 * This assumes signed 16-bit input samples. Exponents are reduced by 9 to
508 * match the 24-bit internal precision for MDCT coefficients.
510 * @return exponent shift
512 static int normalize_samples(AC3EncodeContext *s)
514 int v = 14 - log2_tab(s->windowed_samples, AC3_WINDOW_SIZE);
516 lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
522 * Apply the MDCT to input samples to generate frequency coefficients.
523 * This applies the KBD window and normalizes the input to reduce precision
524 * loss due to fixed-point calculations.
526 static void apply_mdct(AC3EncodeContext *s)
530 for (ch = 0; ch < s->channels; ch++) {
531 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
532 AC3Block *block = &s->blocks[blk];
533 const SampleType *input_samples = &s->planar_samples[ch][blk * AC3_BLOCK_SIZE];
535 apply_window(s->windowed_samples, input_samples, s->mdct.window, AC3_WINDOW_SIZE);
537 block->exp_shift[ch] = normalize_samples(s);
539 mdct512(&s->mdct, block->mdct_coef[ch], s->windowed_samples);
546 * Initialize exponent tables.
548 static av_cold void exponent_init(AC3EncodeContext *s)
551 for (i = 73; i < 256; i++) {
552 exponent_group_tab[0][i] = (i - 1) / 3;
553 exponent_group_tab[1][i] = (i + 2) / 6;
554 exponent_group_tab[2][i] = (i + 8) / 12;
557 exponent_group_tab[0][7] = 2;
562 * Extract exponents from the MDCT coefficients.
563 * This takes into account the normalization that was done to the input samples
564 * by adjusting the exponents by the exponent shift values.
566 static void extract_exponents(AC3EncodeContext *s)
570 for (ch = 0; ch < s->channels; ch++) {
571 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
572 AC3Block *block = &s->blocks[blk];
573 for (i = 0; i < AC3_MAX_COEFS; i++) {
575 int v = abs(SCALE_COEF(block->mdct_coef[ch][i]));
579 e = 23 - av_log2(v) + block->exp_shift[ch];
582 block->mdct_coef[ch][i] = 0;
585 block->exp[ch][i] = e;
593 * Exponent Difference Threshold.
594 * New exponents are sent if their SAD exceed this number.
596 #define EXP_DIFF_THRESHOLD 1000
600 * Calculate exponent strategies for all blocks in a single channel.
602 static void compute_exp_strategy_ch(AC3EncodeContext *s, uint8_t *exp_strategy,
608 /* estimate if the exponent variation & decide if they should be
609 reused in the next frame */
610 exp_strategy[0] = EXP_NEW;
611 for (blk = 1; blk < AC3_MAX_BLOCKS; blk++) {
612 exp_diff = s->dsp.sad[0](NULL, exp[blk], exp[blk-1], 16, 16);
613 if (exp_diff > EXP_DIFF_THRESHOLD)
614 exp_strategy[blk] = EXP_NEW;
616 exp_strategy[blk] = EXP_REUSE;
620 /* now select the encoding strategy type : if exponents are often
621 recoded, we use a coarse encoding */
623 while (blk < AC3_MAX_BLOCKS) {
625 while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1] == EXP_REUSE)
627 switch (blk1 - blk) {
628 case 1: exp_strategy[blk] = EXP_D45; break;
630 case 3: exp_strategy[blk] = EXP_D25; break;
631 default: exp_strategy[blk] = EXP_D15; break;
639 * Calculate exponent strategies for all channels.
640 * Array arrangement is reversed to simplify the per-channel calculation.
642 static void compute_exp_strategy(AC3EncodeContext *s)
644 uint8_t *exp1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
645 uint8_t exp_str1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
648 for (ch = 0; ch < s->fbw_channels; ch++) {
649 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
650 exp1[ch][blk] = s->blocks[blk].exp[ch];
651 exp_str1[ch][blk] = s->blocks[blk].exp_strategy[ch];
654 compute_exp_strategy_ch(s, exp_str1[ch], exp1[ch]);
656 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
657 s->blocks[blk].exp_strategy[ch] = exp_str1[ch][blk];
661 s->blocks[0].exp_strategy[ch] = EXP_D15;
662 for (blk = 1; blk < AC3_MAX_BLOCKS; blk++)
663 s->blocks[blk].exp_strategy[ch] = EXP_REUSE;
669 * Set each encoded exponent in a block to the minimum of itself and the
670 * exponent in the same frequency bin of a following block.
671 * exp[i] = min(exp[i], exp1[i]
673 static void exponent_min(uint8_t *exp, uint8_t *exp1, int n)
676 for (i = 0; i < n; i++) {
677 if (exp1[i] < exp[i])
684 * Update the exponents so that they are the ones the decoder will decode.
686 static void encode_exponents_blk_ch(uint8_t *exp, int nb_exps, int exp_strategy)
690 nb_groups = exponent_group_tab[exp_strategy-1][nb_exps] * 3;
692 /* for each group, compute the minimum exponent */
693 switch(exp_strategy) {
695 for (i = 1, k = 1; i <= nb_groups; i++) {
696 uint8_t exp_min = exp[k];
697 if (exp[k+1] < exp_min)
704 for (i = 1, k = 1; i <= nb_groups; i++) {
705 uint8_t exp_min = exp[k];
706 if (exp[k+1] < exp_min)
708 if (exp[k+2] < exp_min)
710 if (exp[k+3] < exp_min)
718 /* constraint for DC exponent */
722 /* decrease the delta between each groups to within 2 so that they can be
723 differentially encoded */
724 for (i = 1; i <= nb_groups; i++)
725 exp[i] = FFMIN(exp[i], exp[i-1] + 2);
728 exp[i] = FFMIN(exp[i], exp[i+1] + 2);
730 /* now we have the exponent values the decoder will see */
731 switch (exp_strategy) {
733 for (i = nb_groups, k = nb_groups * 2; i > 0; i--) {
734 uint8_t exp1 = exp[i];
740 for (i = nb_groups, k = nb_groups * 4; i > 0; i--) {
741 exp[k] = exp[k-1] = exp[k-2] = exp[k-3] = exp[i];
750 * Encode exponents from original extracted form to what the decoder will see.
751 * This copies and groups exponents based on exponent strategy and reduces
752 * deltas between adjacent exponent groups so that they can be differentially
755 static void encode_exponents(AC3EncodeContext *s)
757 int blk, blk1, blk2, ch;
758 AC3Block *block, *block1, *block2;
760 for (ch = 0; ch < s->channels; ch++) {
762 block = &s->blocks[0];
763 while (blk < AC3_MAX_BLOCKS) {
766 /* for the EXP_REUSE case we select the min of the exponents */
767 while (blk1 < AC3_MAX_BLOCKS && block1->exp_strategy[ch] == EXP_REUSE) {
768 exponent_min(block->exp[ch], block1->exp[ch], s->nb_coefs[ch]);
772 encode_exponents_blk_ch(block->exp[ch], s->nb_coefs[ch],
773 block->exp_strategy[ch]);
774 /* copy encoded exponents for reuse case */
776 for (blk2 = blk+1; blk2 < blk1; blk2++, block2++) {
777 memcpy(block2->exp[ch], block->exp[ch],
778 s->nb_coefs[ch] * sizeof(uint8_t));
789 * 3 delta-encoded exponents are in each 7-bit group. The number of groups
790 * varies depending on exponent strategy and bandwidth.
792 static void group_exponents(AC3EncodeContext *s)
795 int group_size, nb_groups, bit_count;
797 int delta0, delta1, delta2;
801 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
802 AC3Block *block = &s->blocks[blk];
803 for (ch = 0; ch < s->channels; ch++) {
804 if (block->exp_strategy[ch] == EXP_REUSE) {
807 group_size = block->exp_strategy[ch] + (block->exp_strategy[ch] == EXP_D45);
808 nb_groups = exponent_group_tab[block->exp_strategy[ch]-1][s->nb_coefs[ch]];
809 bit_count += 4 + (nb_groups * 7);
814 block->grouped_exp[ch][0] = exp1;
816 /* remaining exponents are delta encoded */
817 for (i = 1; i <= nb_groups; i++) {
818 /* merge three delta in one code */
822 delta0 = exp1 - exp0 + 2;
827 delta1 = exp1 - exp0 + 2;
832 delta2 = exp1 - exp0 + 2;
834 block->grouped_exp[ch][i] = ((delta0 * 5 + delta1) * 5) + delta2;
839 s->exponent_bits = bit_count;
844 * Calculate final exponents from the supplied MDCT coefficients and exponent shift.
845 * Extract exponents from MDCT coefficients, calculate exponent strategies,
846 * and encode final exponents.
848 static void process_exponents(AC3EncodeContext *s)
850 extract_exponents(s);
852 compute_exp_strategy(s);
861 * Count frame bits that are based solely on fixed parameters.
862 * This only has to be run once when the encoder is initialized.
864 static void count_frame_bits_fixed(AC3EncodeContext *s)
866 static const int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };
871 * no dynamic range codes
872 * no channel coupling
874 * bit allocation parameters do not change between blocks
875 * SNR offsets do not change between blocks
876 * no delta bit allocation
883 frame_bits += frame_bits_inc[s->channel_mode];
886 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
887 frame_bits += s->fbw_channels * 2 + 2; /* blksw * c, dithflag * c, dynrnge, cplstre */
888 if (s->channel_mode == AC3_CHMODE_STEREO) {
889 frame_bits++; /* rematstr */
893 frame_bits += 2 * s->fbw_channels; /* chexpstr[2] * c */
895 frame_bits++; /* lfeexpstr */
896 frame_bits++; /* baie */
897 frame_bits++; /* snr */
898 frame_bits += 2; /* delta / skip */
900 frame_bits++; /* cplinu for block 0 */
902 /* sdcycod[2], fdcycod[2], sgaincod[2], dbpbcod[2], floorcod[3] */
904 /* (fsnoffset[4] + fgaincod[4]) * c */
905 frame_bits += 2*4 + 3 + 6 + s->channels * (4 + 3);
907 /* auxdatae, crcrsv */
913 s->frame_bits_fixed = frame_bits;
918 * Initialize bit allocation.
919 * Set default parameter codes and calculate parameter values.
921 static void bit_alloc_init(AC3EncodeContext *s)
925 /* init default parameters */
926 s->slow_decay_code = 2;
927 s->fast_decay_code = 1;
928 s->slow_gain_code = 1;
929 s->db_per_bit_code = 3;
931 for (ch = 0; ch < s->channels; ch++)
932 s->fast_gain_code[ch] = 4;
934 /* initial snr offset */
935 s->coarse_snr_offset = 40;
937 /* compute real values */
938 /* currently none of these values change during encoding, so we can just
939 set them once at initialization */
940 s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->bit_alloc.sr_shift;
941 s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->bit_alloc.sr_shift;
942 s->bit_alloc.slow_gain = ff_ac3_slow_gain_tab[s->slow_gain_code];
943 s->bit_alloc.db_per_bit = ff_ac3_db_per_bit_tab[s->db_per_bit_code];
944 s->bit_alloc.floor = ff_ac3_floor_tab[s->floor_code];
946 count_frame_bits_fixed(s);
951 * Count the bits used to encode the frame, minus exponents and mantissas.
952 * Bits based on fixed parameters have already been counted, so now we just
953 * have to add the bits based on parameters that change during encoding.
955 static void count_frame_bits(AC3EncodeContext *s)
960 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
961 uint8_t *exp_strategy = s->blocks[blk].exp_strategy;
962 for (ch = 0; ch < s->fbw_channels; ch++) {
963 if (exp_strategy[ch] != EXP_REUSE)
964 frame_bits += 6 + 2; /* chbwcod[6], gainrng[2] */
967 s->frame_bits = s->frame_bits_fixed + frame_bits;
972 * Calculate the number of bits needed to encode a set of mantissas.
974 static int compute_mantissa_size(int mant_cnt[5], uint8_t *bap, int nb_coefs)
979 for (i = 0; i < nb_coefs; i++) {
982 // bap=1 to bap=4 will be counted in compute_mantissa_size_final
984 } else if (b <= 13) {
985 // bap=5 to bap=13 use (bap-1) bits
988 // bap=14 uses 14 bits and bap=15 uses 16 bits
989 bits += (b == 14) ? 14 : 16;
997 * Finalize the mantissa bit count by adding in the grouped mantissas.
999 static int compute_mantissa_size_final(int mant_cnt[5])
1001 // bap=1 : 3 mantissas in 5 bits
1002 int bits = (mant_cnt[1] / 3) * 5;
1003 // bap=2 : 3 mantissas in 7 bits
1004 // bap=4 : 2 mantissas in 7 bits
1005 bits += ((mant_cnt[2] / 3) + (mant_cnt[4] >> 1)) * 7;
1006 // bap=3 : each mantissa is 3 bits
1007 bits += mant_cnt[3] * 3;
1013 * Calculate masking curve based on the final exponents.
1014 * Also calculate the power spectral densities to use in future calculations.
1016 static void bit_alloc_masking(AC3EncodeContext *s)
1020 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
1021 AC3Block *block = &s->blocks[blk];
1022 for (ch = 0; ch < s->channels; ch++) {
1023 /* We only need psd and mask for calculating bap.
1024 Since we currently do not calculate bap when exponent
1025 strategy is EXP_REUSE we do not need to calculate psd or mask. */
1026 if (block->exp_strategy[ch] != EXP_REUSE) {
1027 ff_ac3_bit_alloc_calc_psd(block->exp[ch], 0,
1029 block->psd[ch], block->band_psd[ch]);
1030 ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, block->band_psd[ch],
1032 ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],
1033 ch == s->lfe_channel,
1034 DBA_NONE, 0, NULL, NULL, NULL,
1043 * Ensure that bap for each block and channel point to the current bap_buffer.
1044 * They may have been switched during the bit allocation search.
1046 static void reset_block_bap(AC3EncodeContext *s)
1049 if (s->blocks[0].bap[0] == s->bap_buffer)
1051 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
1052 for (ch = 0; ch < s->channels; ch++) {
1053 s->blocks[blk].bap[ch] = &s->bap_buffer[AC3_MAX_COEFS * (blk * s->channels + ch)];
1060 * Run the bit allocation with a given SNR offset.
1061 * This calculates the bit allocation pointers that will be used to determine
1062 * the quantization of each mantissa.
1063 * @return the number of bits needed for mantissas if the given SNR offset is
1066 static int bit_alloc(AC3EncodeContext *s, int snr_offset)
1072 snr_offset = (snr_offset - 240) << 2;
1076 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
1077 AC3Block *block = &s->blocks[blk];
1078 // initialize grouped mantissa counts. these are set so that they are
1079 // padded to the next whole group size when bits are counted in
1080 // compute_mantissa_size_final
1081 mant_cnt[0] = mant_cnt[3] = 0;
1082 mant_cnt[1] = mant_cnt[2] = 2;
1084 for (ch = 0; ch < s->channels; ch++) {
1085 /* Currently the only bit allocation parameters which vary across
1086 blocks within a frame are the exponent values. We can take
1087 advantage of that by reusing the bit allocation pointers
1088 whenever we reuse exponents. */
1089 if (block->exp_strategy[ch] == EXP_REUSE) {
1090 memcpy(block->bap[ch], s->blocks[blk-1].bap[ch], AC3_MAX_COEFS);
1092 ff_ac3_bit_alloc_calc_bap(block->mask[ch], block->psd[ch], 0,
1093 s->nb_coefs[ch], snr_offset,
1094 s->bit_alloc.floor, ff_ac3_bap_tab,
1097 mantissa_bits += compute_mantissa_size(mant_cnt, block->bap[ch], s->nb_coefs[ch]);
1099 mantissa_bits += compute_mantissa_size_final(mant_cnt);
1101 return mantissa_bits;
1106 * Constant bitrate bit allocation search.
1107 * Find the largest SNR offset that will allow data to fit in the frame.
1109 static int cbr_bit_allocation(AC3EncodeContext *s)
1113 int snr_offset, snr_incr;
1115 bits_left = 8 * s->frame_size - (s->frame_bits + s->exponent_bits);
1117 snr_offset = s->coarse_snr_offset << 4;
1119 while (snr_offset >= 0 &&
1120 bit_alloc(s, snr_offset) > bits_left) {
1124 return AVERROR(EINVAL);
1126 FFSWAP(uint8_t *, s->bap_buffer, s->bap1_buffer);
1127 for (snr_incr = 64; snr_incr > 0; snr_incr >>= 2) {
1128 while (snr_offset + 64 <= 1023 &&
1129 bit_alloc(s, snr_offset + snr_incr) <= bits_left) {
1130 snr_offset += snr_incr;
1131 FFSWAP(uint8_t *, s->bap_buffer, s->bap1_buffer);
1134 FFSWAP(uint8_t *, s->bap_buffer, s->bap1_buffer);
1137 s->coarse_snr_offset = snr_offset >> 4;
1138 for (ch = 0; ch < s->channels; ch++)
1139 s->fine_snr_offset[ch] = snr_offset & 0xF;
1146 * Downgrade exponent strategies to reduce the bits used by the exponents.
1147 * This is a fallback for when bit allocation fails with the normal exponent
1148 * strategies. Each time this function is run it only downgrades the
1149 * strategy in 1 channel of 1 block.
1150 * @return non-zero if downgrade was unsuccessful
1152 static int downgrade_exponents(AC3EncodeContext *s)
1156 for (ch = 0; ch < s->fbw_channels; ch++) {
1157 for (blk = AC3_MAX_BLOCKS-1; blk >= 0; blk--) {
1158 if (s->blocks[blk].exp_strategy[ch] == EXP_D15) {
1159 s->blocks[blk].exp_strategy[ch] = EXP_D25;
1164 for (ch = 0; ch < s->fbw_channels; ch++) {
1165 for (blk = AC3_MAX_BLOCKS-1; blk >= 0; blk--) {
1166 if (s->blocks[blk].exp_strategy[ch] == EXP_D25) {
1167 s->blocks[blk].exp_strategy[ch] = EXP_D45;
1172 for (ch = 0; ch < s->fbw_channels; ch++) {
1173 /* block 0 cannot reuse exponents, so only downgrade D45 to REUSE if
1174 the block number > 0 */
1175 for (blk = AC3_MAX_BLOCKS-1; blk > 0; blk--) {
1176 if (s->blocks[blk].exp_strategy[ch] > EXP_REUSE) {
1177 s->blocks[blk].exp_strategy[ch] = EXP_REUSE;
1187 * Reduce the bandwidth to reduce the number of bits used for a given SNR offset.
1188 * This is a second fallback for when bit allocation still fails after exponents
1189 * have been downgraded.
1190 * @return non-zero if bandwidth reduction was unsuccessful
1192 static int reduce_bandwidth(AC3EncodeContext *s, int min_bw_code)
1196 if (s->bandwidth_code[0] > min_bw_code) {
1197 for (ch = 0; ch < s->fbw_channels; ch++) {
1198 s->bandwidth_code[ch]--;
1199 s->nb_coefs[ch] = s->bandwidth_code[ch] * 3 + 73;
1208 * Perform bit allocation search.
1209 * Finds the SNR offset value that maximizes quality and fits in the specified
1210 * frame size. Output is the SNR offset and a set of bit allocation pointers
1211 * used to quantize the mantissas.
1213 static int compute_bit_allocation(AC3EncodeContext *s)
1217 count_frame_bits(s);
1219 bit_alloc_masking(s);
1221 ret = cbr_bit_allocation(s);
1223 /* fallback 1: downgrade exponents */
1224 if (!downgrade_exponents(s)) {
1225 extract_exponents(s);
1226 encode_exponents(s);
1228 ret = compute_bit_allocation(s);
1232 /* fallback 2: reduce bandwidth */
1233 /* only do this if the user has not specified a specific cutoff
1235 if (!s->cutoff && !reduce_bandwidth(s, 0)) {
1236 process_exponents(s);
1237 ret = compute_bit_allocation(s);
1241 /* fallbacks were not enough... */
1250 * Symmetric quantization on 'levels' levels.
1252 static inline int sym_quant(int c, int e, int levels)
1257 v = (levels * (c << e)) >> 24;
1259 v = (levels >> 1) + v;
1261 v = (levels * ((-c) << e)) >> 24;
1263 v = (levels >> 1) - v;
1265 assert(v >= 0 && v < levels);
1271 * Asymmetric quantization on 2^qbits levels.
1273 static inline int asym_quant(int c, int e, int qbits)
1277 lshift = e + qbits - 24;
1284 m = (1 << (qbits-1));
1288 return v & ((1 << qbits)-1);
1293 * Quantize a set of mantissas for a single channel in a single block.
1295 static void quantize_mantissas_blk_ch(AC3EncodeContext *s, CoefType *mdct_coef,
1296 int8_t exp_shift, uint8_t *exp,
1297 uint8_t *bap, uint16_t *qmant, int n)
1301 for (i = 0; i < n; i++) {
1303 int c = SCALE_COEF(mdct_coef[i]);
1304 int e = exp[i] - exp_shift;
1311 v = sym_quant(c, e, 3);
1312 switch (s->mant1_cnt) {
1314 s->qmant1_ptr = &qmant[i];
1319 *s->qmant1_ptr += 3 * v;
1324 *s->qmant1_ptr += v;
1331 v = sym_quant(c, e, 5);
1332 switch (s->mant2_cnt) {
1334 s->qmant2_ptr = &qmant[i];
1339 *s->qmant2_ptr += 5 * v;
1344 *s->qmant2_ptr += v;
1351 v = sym_quant(c, e, 7);
1354 v = sym_quant(c, e, 11);
1355 switch (s->mant4_cnt) {
1357 s->qmant4_ptr = &qmant[i];
1362 *s->qmant4_ptr += v;
1369 v = sym_quant(c, e, 15);
1372 v = asym_quant(c, e, 14);
1375 v = asym_quant(c, e, 16);
1378 v = asym_quant(c, e, b - 1);
1387 * Quantize mantissas using coefficients, exponents, and bit allocation pointers.
1389 static void quantize_mantissas(AC3EncodeContext *s)
1394 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
1395 AC3Block *block = &s->blocks[blk];
1396 s->mant1_cnt = s->mant2_cnt = s->mant4_cnt = 0;
1397 s->qmant1_ptr = s->qmant2_ptr = s->qmant4_ptr = NULL;
1399 for (ch = 0; ch < s->channels; ch++) {
1400 quantize_mantissas_blk_ch(s, block->mdct_coef[ch], block->exp_shift[ch],
1401 block->exp[ch], block->bap[ch],
1402 block->qmant[ch], s->nb_coefs[ch]);
1409 * Write the AC-3 frame header to the output bitstream.
1411 static void output_frame_header(AC3EncodeContext *s)
1413 put_bits(&s->pb, 16, 0x0b77); /* frame header */
1414 put_bits(&s->pb, 16, 0); /* crc1: will be filled later */
1415 put_bits(&s->pb, 2, s->bit_alloc.sr_code);
1416 put_bits(&s->pb, 6, s->frame_size_code + (s->frame_size - s->frame_size_min) / 2);
1417 put_bits(&s->pb, 5, s->bitstream_id);
1418 put_bits(&s->pb, 3, s->bitstream_mode);
1419 put_bits(&s->pb, 3, s->channel_mode);
1420 if ((s->channel_mode & 0x01) && s->channel_mode != AC3_CHMODE_MONO)
1421 put_bits(&s->pb, 2, 1); /* XXX -4.5 dB */
1422 if (s->channel_mode & 0x04)
1423 put_bits(&s->pb, 2, 1); /* XXX -6 dB */
1424 if (s->channel_mode == AC3_CHMODE_STEREO)
1425 put_bits(&s->pb, 2, 0); /* surround not indicated */
1426 put_bits(&s->pb, 1, s->lfe_on); /* LFE */
1427 put_bits(&s->pb, 5, 31); /* dialog norm: -31 db */
1428 put_bits(&s->pb, 1, 0); /* no compression control word */
1429 put_bits(&s->pb, 1, 0); /* no lang code */
1430 put_bits(&s->pb, 1, 0); /* no audio production info */
1431 put_bits(&s->pb, 1, 0); /* no copyright */
1432 put_bits(&s->pb, 1, 1); /* original bitstream */
1433 put_bits(&s->pb, 1, 0); /* no time code 1 */
1434 put_bits(&s->pb, 1, 0); /* no time code 2 */
1435 put_bits(&s->pb, 1, 0); /* no additional bit stream info */
1440 * Write one audio block to the output bitstream.
1442 static void output_audio_block(AC3EncodeContext *s, int block_num)
1444 int ch, i, baie, rbnd;
1445 AC3Block *block = &s->blocks[block_num];
1447 /* block switching */
1448 for (ch = 0; ch < s->fbw_channels; ch++)
1449 put_bits(&s->pb, 1, 0);
1452 for (ch = 0; ch < s->fbw_channels; ch++)
1453 put_bits(&s->pb, 1, 1);
1455 /* dynamic range codes */
1456 put_bits(&s->pb, 1, 0);
1458 /* channel coupling */
1460 put_bits(&s->pb, 1, 1); /* coupling strategy present */
1461 put_bits(&s->pb, 1, 0); /* no coupling strategy */
1463 put_bits(&s->pb, 1, 0); /* no new coupling strategy */
1466 /* stereo rematrixing */
1467 if (s->channel_mode == AC3_CHMODE_STEREO) {
1469 /* first block must define rematrixing (rematstr) */
1470 put_bits(&s->pb, 1, 1);
1472 /* dummy rematrixing rematflg(1:4)=0 */
1473 for (rbnd = 0; rbnd < 4; rbnd++)
1474 put_bits(&s->pb, 1, 0);
1476 /* no matrixing (but should be used in the future) */
1477 put_bits(&s->pb, 1, 0);
1481 /* exponent strategy */
1482 for (ch = 0; ch < s->fbw_channels; ch++)
1483 put_bits(&s->pb, 2, block->exp_strategy[ch]);
1485 put_bits(&s->pb, 1, block->exp_strategy[s->lfe_channel]);
1488 for (ch = 0; ch < s->fbw_channels; ch++) {
1489 if (block->exp_strategy[ch] != EXP_REUSE)
1490 put_bits(&s->pb, 6, s->bandwidth_code[ch]);
1494 for (ch = 0; ch < s->channels; ch++) {
1497 if (block->exp_strategy[ch] == EXP_REUSE)
1501 put_bits(&s->pb, 4, block->grouped_exp[ch][0]);
1503 /* exponent groups */
1504 nb_groups = exponent_group_tab[block->exp_strategy[ch]-1][s->nb_coefs[ch]];
1505 for (i = 1; i <= nb_groups; i++)
1506 put_bits(&s->pb, 7, block->grouped_exp[ch][i]);
1508 /* gain range info */
1509 if (ch != s->lfe_channel)
1510 put_bits(&s->pb, 2, 0);
1513 /* bit allocation info */
1514 baie = (block_num == 0);
1515 put_bits(&s->pb, 1, baie);
1517 put_bits(&s->pb, 2, s->slow_decay_code);
1518 put_bits(&s->pb, 2, s->fast_decay_code);
1519 put_bits(&s->pb, 2, s->slow_gain_code);
1520 put_bits(&s->pb, 2, s->db_per_bit_code);
1521 put_bits(&s->pb, 3, s->floor_code);
1525 put_bits(&s->pb, 1, baie);
1527 put_bits(&s->pb, 6, s->coarse_snr_offset);
1528 for (ch = 0; ch < s->channels; ch++) {
1529 put_bits(&s->pb, 4, s->fine_snr_offset[ch]);
1530 put_bits(&s->pb, 3, s->fast_gain_code[ch]);
1534 put_bits(&s->pb, 1, 0); /* no delta bit allocation */
1535 put_bits(&s->pb, 1, 0); /* no data to skip */
1538 for (ch = 0; ch < s->channels; ch++) {
1540 for (i = 0; i < s->nb_coefs[ch]; i++) {
1541 q = block->qmant[ch][i];
1542 b = block->bap[ch][i];
1545 case 1: if (q != 128) put_bits(&s->pb, 5, q); break;
1546 case 2: if (q != 128) put_bits(&s->pb, 7, q); break;
1547 case 3: put_bits(&s->pb, 3, q); break;
1548 case 4: if (q != 128) put_bits(&s->pb, 7, q); break;
1549 case 14: put_bits(&s->pb, 14, q); break;
1550 case 15: put_bits(&s->pb, 16, q); break;
1551 default: put_bits(&s->pb, b-1, q); break;
1558 /** CRC-16 Polynomial */
1559 #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))
1562 static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)
1579 static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)
1585 r = mul_poly(r, a, poly);
1586 a = mul_poly(a, a, poly);
1594 * Fill the end of the frame with 0's and compute the two CRCs.
1596 static void output_frame_end(AC3EncodeContext *s)
1598 const AVCRC *crc_ctx = av_crc_get_table(AV_CRC_16_ANSI);
1599 int frame_size_58, pad_bytes, crc1, crc2_partial, crc2, crc_inv;
1602 frame_size_58 = ((s->frame_size >> 2) + (s->frame_size >> 4)) << 1;
1604 /* pad the remainder of the frame with zeros */
1605 flush_put_bits(&s->pb);
1607 pad_bytes = s->frame_size - (put_bits_ptr(&s->pb) - frame) - 2;
1608 assert(pad_bytes >= 0);
1610 memset(put_bits_ptr(&s->pb), 0, pad_bytes);
1613 /* this is not so easy because it is at the beginning of the data... */
1614 crc1 = av_bswap16(av_crc(crc_ctx, 0, frame + 4, frame_size_58 - 4));
1615 crc_inv = s->crc_inv[s->frame_size > s->frame_size_min];
1616 crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);
1617 AV_WB16(frame + 2, crc1);
1620 crc2_partial = av_crc(crc_ctx, 0, frame + frame_size_58,
1621 s->frame_size - frame_size_58 - 3);
1622 crc2 = av_crc(crc_ctx, crc2_partial, frame + s->frame_size - 3, 1);
1623 /* ensure crc2 does not match sync word by flipping crcrsv bit if needed */
1624 if (crc2 == 0x770B) {
1625 frame[s->frame_size - 3] ^= 0x1;
1626 crc2 = av_crc(crc_ctx, crc2_partial, frame + s->frame_size - 3, 1);
1628 crc2 = av_bswap16(crc2);
1629 AV_WB16(frame + s->frame_size - 2, crc2);
1634 * Write the frame to the output bitstream.
1636 static void output_frame(AC3EncodeContext *s, unsigned char *frame)
1640 init_put_bits(&s->pb, frame, AC3_MAX_CODED_FRAME_SIZE);
1642 output_frame_header(s);
1644 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
1645 output_audio_block(s, blk);
1647 output_frame_end(s);
1652 * Encode a single AC-3 frame.
1654 static int ac3_encode_frame(AVCodecContext *avctx, unsigned char *frame,
1655 int buf_size, void *data)
1657 AC3EncodeContext *s = avctx->priv_data;
1658 const SampleType *samples = data;
1661 if (s->bit_alloc.sr_code == 1)
1662 adjust_frame_size(s);
1664 deinterleave_input_samples(s, samples);
1668 process_exponents(s);
1670 ret = compute_bit_allocation(s);
1672 av_log(avctx, AV_LOG_ERROR, "Bit allocation failed. Try increasing the bitrate.\n");
1676 quantize_mantissas(s);
1678 output_frame(s, frame);
1680 return s->frame_size;
1685 * Finalize encoding and free any memory allocated by the encoder.
1687 static av_cold int ac3_encode_close(AVCodecContext *avctx)
1690 AC3EncodeContext *s = avctx->priv_data;
1692 for (ch = 0; ch < s->channels; ch++)
1693 av_freep(&s->planar_samples[ch]);
1694 av_freep(&s->planar_samples);
1695 av_freep(&s->bap_buffer);
1696 av_freep(&s->bap1_buffer);
1697 av_freep(&s->mdct_coef_buffer);
1698 av_freep(&s->exp_buffer);
1699 av_freep(&s->grouped_exp_buffer);
1700 av_freep(&s->psd_buffer);
1701 av_freep(&s->band_psd_buffer);
1702 av_freep(&s->mask_buffer);
1703 av_freep(&s->qmant_buffer);
1704 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
1705 AC3Block *block = &s->blocks[blk];
1706 av_freep(&block->bap);
1707 av_freep(&block->mdct_coef);
1708 av_freep(&block->exp);
1709 av_freep(&block->grouped_exp);
1710 av_freep(&block->psd);
1711 av_freep(&block->band_psd);
1712 av_freep(&block->mask);
1713 av_freep(&block->qmant);
1718 av_freep(&avctx->coded_frame);
1724 * Set channel information during initialization.
1726 static av_cold int set_channel_info(AC3EncodeContext *s, int channels,
1727 int64_t *channel_layout)
1731 if (channels < 1 || channels > AC3_MAX_CHANNELS)
1732 return AVERROR(EINVAL);
1733 if ((uint64_t)*channel_layout > 0x7FF)
1734 return AVERROR(EINVAL);
1735 ch_layout = *channel_layout;
1737 ch_layout = avcodec_guess_channel_layout(channels, CODEC_ID_AC3, NULL);
1738 if (av_get_channel_layout_nb_channels(ch_layout) != channels)
1739 return AVERROR(EINVAL);
1741 s->lfe_on = !!(ch_layout & AV_CH_LOW_FREQUENCY);
1742 s->channels = channels;
1743 s->fbw_channels = channels - s->lfe_on;
1744 s->lfe_channel = s->lfe_on ? s->fbw_channels : -1;
1746 ch_layout -= AV_CH_LOW_FREQUENCY;
1748 switch (ch_layout) {
1749 case AV_CH_LAYOUT_MONO: s->channel_mode = AC3_CHMODE_MONO; break;
1750 case AV_CH_LAYOUT_STEREO: s->channel_mode = AC3_CHMODE_STEREO; break;
1751 case AV_CH_LAYOUT_SURROUND: s->channel_mode = AC3_CHMODE_3F; break;
1752 case AV_CH_LAYOUT_2_1: s->channel_mode = AC3_CHMODE_2F1R; break;
1753 case AV_CH_LAYOUT_4POINT0: s->channel_mode = AC3_CHMODE_3F1R; break;
1754 case AV_CH_LAYOUT_QUAD:
1755 case AV_CH_LAYOUT_2_2: s->channel_mode = AC3_CHMODE_2F2R; break;
1756 case AV_CH_LAYOUT_5POINT0:
1757 case AV_CH_LAYOUT_5POINT0_BACK: s->channel_mode = AC3_CHMODE_3F2R; break;
1759 return AVERROR(EINVAL);
1762 s->channel_map = ff_ac3_enc_channel_map[s->channel_mode][s->lfe_on];
1763 *channel_layout = ch_layout;
1765 *channel_layout |= AV_CH_LOW_FREQUENCY;
1771 static av_cold int validate_options(AVCodecContext *avctx, AC3EncodeContext *s)
1775 /* validate channel layout */
1776 if (!avctx->channel_layout) {
1777 av_log(avctx, AV_LOG_WARNING, "No channel layout specified. The "
1778 "encoder will guess the layout, but it "
1779 "might be incorrect.\n");
1781 ret = set_channel_info(s, avctx->channels, &avctx->channel_layout);
1783 av_log(avctx, AV_LOG_ERROR, "invalid channel layout\n");
1787 /* validate sample rate */
1788 for (i = 0; i < 9; i++) {
1789 if ((ff_ac3_sample_rate_tab[i / 3] >> (i % 3)) == avctx->sample_rate)
1793 av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
1794 return AVERROR(EINVAL);
1796 s->sample_rate = avctx->sample_rate;
1797 s->bit_alloc.sr_shift = i % 3;
1798 s->bit_alloc.sr_code = i / 3;
1800 /* validate bit rate */
1801 for (i = 0; i < 19; i++) {
1802 if ((ff_ac3_bitrate_tab[i] >> s->bit_alloc.sr_shift)*1000 == avctx->bit_rate)
1806 av_log(avctx, AV_LOG_ERROR, "invalid bit rate\n");
1807 return AVERROR(EINVAL);
1809 s->bit_rate = avctx->bit_rate;
1810 s->frame_size_code = i << 1;
1812 /* validate cutoff */
1813 if (avctx->cutoff < 0) {
1814 av_log(avctx, AV_LOG_ERROR, "invalid cutoff frequency\n");
1815 return AVERROR(EINVAL);
1817 s->cutoff = avctx->cutoff;
1818 if (s->cutoff > (s->sample_rate >> 1))
1819 s->cutoff = s->sample_rate >> 1;
1826 * Set bandwidth for all channels.
1827 * The user can optionally supply a cutoff frequency. Otherwise an appropriate
1828 * default value will be used.
1830 static av_cold void set_bandwidth(AC3EncodeContext *s)
1835 /* calculate bandwidth based on user-specified cutoff frequency */
1837 fbw_coeffs = s->cutoff * 2 * AC3_MAX_COEFS / s->sample_rate;
1838 bw_code = av_clip((fbw_coeffs - 73) / 3, 0, 60);
1840 /* use default bandwidth setting */
1841 /* XXX: should compute the bandwidth according to the frame
1842 size, so that we avoid annoying high frequency artifacts */
1846 /* set number of coefficients for each channel */
1847 for (ch = 0; ch < s->fbw_channels; ch++) {
1848 s->bandwidth_code[ch] = bw_code;
1849 s->nb_coefs[ch] = bw_code * 3 + 73;
1852 s->nb_coefs[s->lfe_channel] = 7; /* LFE channel always has 7 coefs */
1856 static av_cold int allocate_buffers(AVCodecContext *avctx)
1859 AC3EncodeContext *s = avctx->priv_data;
1861 FF_ALLOC_OR_GOTO(avctx, s->planar_samples, s->channels * sizeof(*s->planar_samples),
1863 for (ch = 0; ch < s->channels; ch++) {
1864 FF_ALLOCZ_OR_GOTO(avctx, s->planar_samples[ch],
1865 (AC3_FRAME_SIZE+AC3_BLOCK_SIZE) * sizeof(**s->planar_samples),
1868 FF_ALLOC_OR_GOTO(avctx, s->bap_buffer, AC3_MAX_BLOCKS * s->channels *
1869 AC3_MAX_COEFS * sizeof(*s->bap_buffer), alloc_fail);
1870 FF_ALLOC_OR_GOTO(avctx, s->bap1_buffer, AC3_MAX_BLOCKS * s->channels *
1871 AC3_MAX_COEFS * sizeof(*s->bap1_buffer), alloc_fail);
1872 FF_ALLOC_OR_GOTO(avctx, s->mdct_coef_buffer, AC3_MAX_BLOCKS * s->channels *
1873 AC3_MAX_COEFS * sizeof(*s->mdct_coef_buffer), alloc_fail);
1874 FF_ALLOC_OR_GOTO(avctx, s->exp_buffer, AC3_MAX_BLOCKS * s->channels *
1875 AC3_MAX_COEFS * sizeof(*s->exp_buffer), alloc_fail);
1876 FF_ALLOC_OR_GOTO(avctx, s->grouped_exp_buffer, AC3_MAX_BLOCKS * s->channels *
1877 128 * sizeof(*s->grouped_exp_buffer), alloc_fail);
1878 FF_ALLOC_OR_GOTO(avctx, s->psd_buffer, AC3_MAX_BLOCKS * s->channels *
1879 AC3_MAX_COEFS * sizeof(*s->psd_buffer), alloc_fail);
1880 FF_ALLOC_OR_GOTO(avctx, s->band_psd_buffer, AC3_MAX_BLOCKS * s->channels *
1881 64 * sizeof(*s->band_psd_buffer), alloc_fail);
1882 FF_ALLOC_OR_GOTO(avctx, s->mask_buffer, AC3_MAX_BLOCKS * s->channels *
1883 64 * sizeof(*s->mask_buffer), alloc_fail);
1884 FF_ALLOC_OR_GOTO(avctx, s->qmant_buffer, AC3_MAX_BLOCKS * s->channels *
1885 AC3_MAX_COEFS * sizeof(*s->qmant_buffer), alloc_fail);
1886 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
1887 AC3Block *block = &s->blocks[blk];
1888 FF_ALLOC_OR_GOTO(avctx, block->bap, s->channels * sizeof(*block->bap),
1890 FF_ALLOCZ_OR_GOTO(avctx, block->mdct_coef, s->channels * sizeof(*block->mdct_coef),
1892 FF_ALLOCZ_OR_GOTO(avctx, block->exp, s->channels * sizeof(*block->exp),
1894 FF_ALLOCZ_OR_GOTO(avctx, block->grouped_exp, s->channels * sizeof(*block->grouped_exp),
1896 FF_ALLOCZ_OR_GOTO(avctx, block->psd, s->channels * sizeof(*block->psd),
1898 FF_ALLOCZ_OR_GOTO(avctx, block->band_psd, s->channels * sizeof(*block->band_psd),
1900 FF_ALLOCZ_OR_GOTO(avctx, block->mask, s->channels * sizeof(*block->mask),
1902 FF_ALLOCZ_OR_GOTO(avctx, block->qmant, s->channels * sizeof(*block->qmant),
1905 for (ch = 0; ch < s->channels; ch++) {
1906 block->bap[ch] = &s->bap_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
1907 block->mdct_coef[ch] = &s->mdct_coef_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
1908 block->exp[ch] = &s->exp_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
1909 block->grouped_exp[ch] = &s->grouped_exp_buffer[128 * (blk * s->channels + ch)];
1910 block->psd[ch] = &s->psd_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
1911 block->band_psd[ch] = &s->band_psd_buffer [64 * (blk * s->channels + ch)];
1912 block->mask[ch] = &s->mask_buffer [64 * (blk * s->channels + ch)];
1913 block->qmant[ch] = &s->qmant_buffer [AC3_MAX_COEFS * (blk * s->channels + ch)];
1919 return AVERROR(ENOMEM);
1924 * Initialize the encoder.
1926 static av_cold int ac3_encode_init(AVCodecContext *avctx)
1928 AC3EncodeContext *s = avctx->priv_data;
1929 int ret, frame_size_58;
1931 avctx->frame_size = AC3_FRAME_SIZE;
1935 ret = validate_options(avctx, s);
1939 s->bitstream_id = 8 + s->bit_alloc.sr_shift;
1940 s->bitstream_mode = 0; /* complete main audio service */
1942 s->frame_size_min = 2 * ff_ac3_frame_size_tab[s->frame_size_code][s->bit_alloc.sr_code];
1943 s->bits_written = 0;
1944 s->samples_written = 0;
1945 s->frame_size = s->frame_size_min;
1947 /* calculate crc_inv for both possible frame sizes */
1948 frame_size_58 = (( s->frame_size >> 2) + ( s->frame_size >> 4)) << 1;
1949 s->crc_inv[0] = pow_poly((CRC16_POLY >> 1), (8 * frame_size_58) - 16, CRC16_POLY);
1950 if (s->bit_alloc.sr_code == 1) {
1951 frame_size_58 = (((s->frame_size+2) >> 2) + ((s->frame_size+2) >> 4)) << 1;
1952 s->crc_inv[1] = pow_poly((CRC16_POLY >> 1), (8 * frame_size_58) - 16, CRC16_POLY);
1961 ret = mdct_init(avctx, &s->mdct, 9);
1965 ret = allocate_buffers(avctx);
1969 avctx->coded_frame= avcodec_alloc_frame();
1971 dsputil_init(&s->dsp, avctx);
1975 ac3_encode_close(avctx);
1981 /*************************************************************************/
1984 #include "libavutil/lfg.h"
1986 #define MDCT_NBITS 9
1987 #define MDCT_SAMPLES (1 << MDCT_NBITS)
1988 #define FN (MDCT_SAMPLES/4)
1991 static void fft_test(AC3MDCTContext *mdct, AVLFG *lfg)
1993 IComplex in[FN], in1[FN];
1995 float sum_re, sum_im, a;
1997 for (i = 0; i < FN; i++) {
1998 in[i].re = av_lfg_get(lfg) % 65535 - 32767;
1999 in[i].im = av_lfg_get(lfg) % 65535 - 32767;
2005 for (k = 0; k < FN; k++) {
2008 for (n = 0; n < FN; n++) {
2009 a = -2 * M_PI * (n * k) / FN;
2010 sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);
2011 sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);
2013 av_log(NULL, AV_LOG_DEBUG, "%3d: %6d,%6d %6.0f,%6.0f\n",
2014 k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);
2019 static void mdct_test(AC3MDCTContext *mdct, AVLFG *lfg)
2021 int16_t input[MDCT_SAMPLES];
2022 int32_t output[AC3_MAX_COEFS];
2023 float input1[MDCT_SAMPLES];
2024 float output1[AC3_MAX_COEFS];
2025 float s, a, err, e, emax;
2028 for (i = 0; i < MDCT_SAMPLES; i++) {
2029 input[i] = (av_lfg_get(lfg) % 65535 - 32767) * 9 / 10;
2030 input1[i] = input[i];
2033 mdct512(mdct, output, input);
2036 for (k = 0; k < AC3_MAX_COEFS; k++) {
2038 for (n = 0; n < MDCT_SAMPLES; n++) {
2039 a = (2*M_PI*(2*n+1+MDCT_SAMPLES/2)*(2*k+1) / (4 * MDCT_SAMPLES));
2040 s += input1[n] * cos(a);
2042 output1[k] = -2 * s / MDCT_SAMPLES;
2047 for (i = 0; i < AC3_MAX_COEFS; i++) {
2048 av_log(NULL, AV_LOG_DEBUG, "%3d: %7d %7.0f\n", i, output[i], output1[i]);
2049 e = output[i] - output1[i];
2054 av_log(NULL, AV_LOG_DEBUG, "err2=%f emax=%f\n", err / AC3_MAX_COEFS, emax);
2061 AC3MDCTContext mdct;
2064 av_log_set_level(AV_LOG_DEBUG);
2065 mdct_init(&mdct, 9);
2067 fft_test(&mdct, &lfg);
2068 mdct_test(&mdct, &lfg);
2075 AVCodec ac3_encoder = {
2079 sizeof(AC3EncodeContext),
2084 .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
2085 .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
2086 .channel_layouts = ac3_channel_layouts,