2 * The simplest AC-3 encoder
3 * Copyright (c) 2000 Fabrice Bellard
5 * This file is part of FFmpeg.
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 * The simplest AC-3 encoder.
29 #include "libavcore/audioconvert.h"
30 #include "libavutil/crc.h"
34 #include "audioconvert.h"
38 #define MDCT_SAMPLES (1 << MDCT_NBITS)
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 /** Scale a float value by 2^15, convert to an integer, and clip to int16_t range. */
47 #define FIX15(a) av_clip_int16(SCALE_FLOAT(a, 15))
52 * Used in fixed-point MDCT calculation.
54 typedef struct IComplex {
59 * Data for a single audio block.
61 typedef struct AC3Block {
62 int32_t mdct_coef[AC3_MAX_CHANNELS][AC3_MAX_COEFS];
63 uint8_t exp[AC3_MAX_CHANNELS][AC3_MAX_COEFS];
64 uint8_t exp_strategy[AC3_MAX_CHANNELS];
65 uint8_t encoded_exp[AC3_MAX_CHANNELS][AC3_MAX_COEFS];
66 uint8_t num_exp_groups[AC3_MAX_CHANNELS];
67 uint8_t grouped_exp[AC3_MAX_CHANNELS][AC3_MAX_EXP_GROUPS];
68 int16_t psd[AC3_MAX_CHANNELS][AC3_MAX_COEFS];
69 int16_t band_psd[AC3_MAX_CHANNELS][AC3_CRITICAL_BANDS];
70 int16_t mask[AC3_MAX_CHANNELS][AC3_CRITICAL_BANDS];
71 int8_t exp_shift[AC3_MAX_CHANNELS];
72 uint16_t qmant[AC3_MAX_CHANNELS][AC3_MAX_COEFS];
76 * AC-3 encoder private context.
78 typedef struct AC3EncodeContext {
79 PutBitContext pb; ///< bitstream writer context
81 AC3Block blocks[AC3_MAX_BLOCKS]; ///< per-block info
83 int bitstream_id; ///< bitstream id (bsid)
84 int bitstream_mode; ///< bitstream mode (bsmod)
86 int bit_rate; ///< target bit rate, in bits-per-second
87 int sample_rate; ///< sampling frequency, in Hz
89 int frame_size_min; ///< minimum frame size in case rounding is necessary
90 int frame_size; ///< current frame size in bytes
91 int frame_size_code; ///< frame size code (frmsizecod)
92 int bits_written; ///< bit count (used to avg. bitrate)
93 int samples_written; ///< sample count (used to avg. bitrate)
95 int fbw_channels; ///< number of full-bandwidth channels (nfchans)
96 int channels; ///< total number of channels (nchans)
97 int lfe_on; ///< indicates if there is an LFE channel (lfeon)
98 int lfe_channel; ///< channel index of the LFE channel
99 int channel_mode; ///< channel mode (acmod)
100 const uint8_t *channel_map; ///< channel map used to reorder channels
102 int bandwidth_code[AC3_MAX_CHANNELS]; ///< bandwidth code (0 to 60) (chbwcod)
103 int nb_coefs[AC3_MAX_CHANNELS];
105 /* bitrate allocation control */
106 int slow_gain_code; ///< slow gain code (sgaincod)
107 int slow_decay_code; ///< slow decay code (sdcycod)
108 int fast_decay_code; ///< fast decay code (fdcycod)
109 int db_per_bit_code; ///< dB/bit code (dbpbcod)
110 int floor_code; ///< floor code (floorcod)
111 AC3BitAllocParameters bit_alloc; ///< bit allocation parameters
112 int coarse_snr_offset; ///< coarse SNR offsets (csnroffst)
113 int fast_gain_code[AC3_MAX_CHANNELS]; ///< fast gain codes (signal-to-mask ratio) (fgaincod)
114 int fine_snr_offset[AC3_MAX_CHANNELS]; ///< fine SNR offsets (fsnroffst)
115 int frame_bits; ///< all frame bits except exponents and mantissas
116 int exponent_bits; ///< number of bits used for exponents
118 /* mantissa encoding */
119 int mant1_cnt, mant2_cnt, mant4_cnt; ///< mantissa counts for bap=1,2,4
120 uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr; ///< mantissa pointers for bap=1,2,4
122 int16_t last_samples[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE]; ///< last 256 samples from previous frame
123 int16_t planar_samples[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE+AC3_FRAME_SIZE];
124 int16_t windowed_samples[AC3_WINDOW_SIZE];
125 uint8_t bap[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];
126 uint8_t bap1[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];
130 /** MDCT and FFT tables */
131 static int16_t costab[64];
132 static int16_t sintab[64];
133 static int16_t xcos1[128];
134 static int16_t xsin1[128];
138 * Adjust the frame size to make the average bit rate match the target bit rate.
139 * This is only needed for 11025, 22050, and 44100 sample rates.
141 static void adjust_frame_size(AC3EncodeContext *s)
143 while (s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {
144 s->bits_written -= s->bit_rate;
145 s->samples_written -= s->sample_rate;
147 s->frame_size = s->frame_size_min +
148 2 * (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
149 s->bits_written += s->frame_size * 8;
150 s->samples_written += AC3_FRAME_SIZE;
155 * Deinterleave input samples.
156 * Channels are reordered from FFmpeg's default order to AC-3 order.
158 static void deinterleave_input_samples(AC3EncodeContext *s,
159 const int16_t *samples)
163 /* deinterleave and remap input samples */
164 for (ch = 0; ch < s->channels; ch++) {
168 /* copy last 256 samples of previous frame to the start of the current frame */
169 memcpy(&s->planar_samples[ch][0], s->last_samples[ch],
170 AC3_BLOCK_SIZE * sizeof(s->planar_samples[0][0]));
174 sptr = samples + s->channel_map[ch];
175 for (i = AC3_BLOCK_SIZE; i < AC3_FRAME_SIZE+AC3_BLOCK_SIZE; i++) {
176 s->planar_samples[ch][i] = *sptr;
180 /* save last 256 samples for next frame */
181 memcpy(s->last_samples[ch], &s->planar_samples[ch][6* AC3_BLOCK_SIZE],
182 AC3_BLOCK_SIZE * sizeof(s->planar_samples[0][0]));
188 * Initialize FFT tables.
189 * @param ln log2(FFT size)
191 static av_cold void fft_init(int ln)
199 for (i = 0; i < n2; i++) {
200 alpha = 2.0 * M_PI * i / n;
201 costab[i] = FIX15(cos(alpha));
202 sintab[i] = FIX15(sin(alpha));
208 * Initialize MDCT tables.
209 * @param nbits log2(MDCT size)
211 static av_cold void mdct_init(int nbits)
220 for (i = 0; i < n4; i++) {
221 float alpha = 2.0 * M_PI * (i + 1.0 / 8.0) / n;
222 xcos1[i] = FIX15(-cos(alpha));
223 xsin1[i] = FIX15(-sin(alpha));
229 #define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1) \
231 int ax, ay, bx, by; \
236 pre = (bx + ax) >> 1; \
237 pim = (by + ay) >> 1; \
238 qre = (bx - ax) >> 1; \
239 qim = (by - ay) >> 1; \
243 /** Complex multiply */
244 #define CMUL(pre, pim, are, aim, bre, bim) \
246 pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15; \
247 pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15; \
252 * Calculate a 2^n point complex FFT on 2^ln points.
253 * @param z complex input/output samples
254 * @param ln log2(FFT size)
256 static void fft(IComplex *z, int ln)
260 register IComplex *p,*q;
266 for (j = 0; j < np; j++) {
267 int k = av_reverse[j] >> (8 - ln);
269 FFSWAP(IComplex, z[k], z[j]);
277 BF(p[0].re, p[0].im, p[1].re, p[1].im,
278 p[0].re, p[0].im, p[1].re, p[1].im);
287 BF(p[0].re, p[0].im, p[2].re, p[2].im,
288 p[0].re, p[0].im, p[2].re, p[2].im);
289 BF(p[1].re, p[1].im, p[3].re, p[3].im,
290 p[1].re, p[1].im, p[3].im, -p[3].re);
302 for (j = 0; j < nblocks; j++) {
303 BF(p->re, p->im, q->re, q->im,
304 p->re, p->im, q->re, q->im);
307 for(l = nblocks; l < np2; l += nblocks) {
308 CMUL(tmp_re, tmp_im, costab[l], -sintab[l], q->re, q->im);
309 BF(p->re, p->im, q->re, q->im,
310 p->re, p->im, tmp_re, tmp_im);
317 nblocks = nblocks >> 1;
318 nloops = nloops << 1;
324 * Calculate a 512-point MDCT
325 * @param out 256 output frequency coefficients
326 * @param in 512 windowed input audio samples
328 static void mdct512(int32_t *out, int16_t *in)
330 int i, re, im, re1, im1;
331 int16_t rot[MDCT_SAMPLES];
332 IComplex x[MDCT_SAMPLES/4];
334 /* shift to simplify computations */
335 for (i = 0; i < MDCT_SAMPLES/4; i++)
336 rot[i] = -in[i + 3*MDCT_SAMPLES/4];
337 for (;i < MDCT_SAMPLES; i++)
338 rot[i] = in[i - MDCT_SAMPLES/4];
341 for (i = 0; i < MDCT_SAMPLES/4; i++) {
342 re = ((int)rot[ 2*i] - (int)rot[MDCT_SAMPLES -1-2*i]) >> 1;
343 im = -((int)rot[MDCT_SAMPLES/2+2*i] - (int)rot[MDCT_SAMPLES/2-1-2*i]) >> 1;
344 CMUL(x[i].re, x[i].im, re, im, -xcos1[i], xsin1[i]);
347 fft(x, MDCT_NBITS - 2);
350 for (i = 0; i < MDCT_SAMPLES/4; i++) {
353 CMUL(re1, im1, re, im, xsin1[i], xcos1[i]);
355 out[MDCT_SAMPLES/2-1-2*i] = re1;
361 * Apply KBD window to input samples prior to MDCT.
363 static void apply_window(int16_t *output, const int16_t *input,
364 const int16_t *window, int n)
369 for (i = 0; i < n2; i++) {
370 output[i] = MUL16(input[i], window[i]) >> 15;
371 output[n-i-1] = MUL16(input[n-i-1], window[i]) >> 15;
377 * Calculate the log2() of the maximum absolute value in an array.
378 * @param tab input array
379 * @param n number of values in the array
380 * @return log2(max(abs(tab[])))
382 static int log2_tab(int16_t *tab, int n)
387 for (i = 0; i < n; i++)
395 * Left-shift each value in an array by a specified amount.
396 * @param tab input array
397 * @param n number of values in the array
398 * @param lshift left shift amount. a negative value means right shift.
400 static void lshift_tab(int16_t *tab, int n, int lshift)
405 for (i = 0; i < n; i++)
407 } else if (lshift < 0) {
409 for (i = 0; i < n; i++)
416 * Normalize the input samples to use the maximum available precision.
417 * This assumes signed 16-bit input samples. Exponents are reduced by 9 to
418 * match the 24-bit internal precision for MDCT coefficients.
420 * @return exponent shift
422 static int normalize_samples(AC3EncodeContext *s)
424 int v = 14 - log2_tab(s->windowed_samples, AC3_WINDOW_SIZE);
426 lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
432 * Apply the MDCT to input samples to generate frequency coefficients.
433 * This applies the KBD window and normalizes the input to reduce precision
434 * loss due to fixed-point calculations.
436 static void apply_mdct(AC3EncodeContext *s)
440 for (ch = 0; ch < s->channels; ch++) {
441 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
442 AC3Block *block = &s->blocks[blk];
443 const int16_t *input_samples = &s->planar_samples[ch][blk * AC3_BLOCK_SIZE];
445 apply_window(s->windowed_samples, input_samples, ff_ac3_window, AC3_WINDOW_SIZE);
447 block->exp_shift[ch] = normalize_samples(s);
449 mdct512(block->mdct_coef[ch], s->windowed_samples);
456 * Extract exponents from the MDCT coefficients.
457 * This takes into account the normalization that was done to the input samples
458 * by adjusting the exponents by the exponent shift values.
460 static void extract_exponents(AC3EncodeContext *s)
464 for (ch = 0; ch < s->channels; ch++) {
465 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
466 AC3Block *block = &s->blocks[blk];
467 for (i = 0; i < AC3_MAX_COEFS; i++) {
469 int v = abs(block->mdct_coef[ch][i]);
473 e = 23 - av_log2(v) + block->exp_shift[ch];
476 block->mdct_coef[ch][i] = 0;
479 block->exp[ch][i] = e;
487 * Calculate the sum of absolute differences (SAD) between 2 sets of exponents.
489 static int calc_exp_diff(uint8_t *exp1, uint8_t *exp2, int n)
493 for (i = 0; i < n; i++)
494 sum += abs(exp1[i] - exp2[i]);
500 * Exponent Difference Threshold.
501 * New exponents are sent if their SAD exceed this number.
503 #define EXP_DIFF_THRESHOLD 1000
507 * Calculate exponent strategies for all blocks in a single channel.
509 static void compute_exp_strategy_ch(uint8_t *exp_strategy, uint8_t **exp)
514 /* estimate if the exponent variation & decide if they should be
515 reused in the next frame */
516 exp_strategy[0] = EXP_NEW;
517 for (blk = 1; blk < AC3_MAX_BLOCKS; blk++) {
518 exp_diff = calc_exp_diff(exp[blk], exp[blk-1], AC3_MAX_COEFS);
519 if (exp_diff > EXP_DIFF_THRESHOLD)
520 exp_strategy[blk] = EXP_NEW;
522 exp_strategy[blk] = EXP_REUSE;
525 /* now select the encoding strategy type : if exponents are often
526 recoded, we use a coarse encoding */
528 while (blk < AC3_MAX_BLOCKS) {
530 while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1] == EXP_REUSE)
532 switch (blk1 - blk) {
533 case 1: exp_strategy[blk] = EXP_D45; break;
535 case 3: exp_strategy[blk] = EXP_D25; break;
536 default: exp_strategy[blk] = EXP_D15; break;
544 * Calculate exponent strategies for all channels.
545 * Array arrangement is reversed to simplify the per-channel calculation.
547 static void compute_exp_strategy(AC3EncodeContext *s)
549 uint8_t *exp1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
550 uint8_t exp_str1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
553 for (ch = 0; ch < s->fbw_channels; ch++) {
554 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
555 exp1[ch][blk] = s->blocks[blk].exp[ch];
556 exp_str1[ch][blk] = s->blocks[blk].exp_strategy[ch];
559 compute_exp_strategy_ch(exp_str1[ch], exp1[ch]);
561 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
562 s->blocks[blk].exp_strategy[ch] = exp_str1[ch][blk];
566 s->blocks[0].exp_strategy[ch] = EXP_D15;
567 for (blk = 1; blk < AC3_MAX_BLOCKS; blk++)
568 s->blocks[blk].exp_strategy[ch] = EXP_REUSE;
574 * Set each encoded exponent in a block to the minimum of itself and the
575 * exponent in the same frequency bin of a following block.
576 * exp[i] = min(exp[i], exp1[i]
578 static void exponent_min(uint8_t *exp, uint8_t *exp1, int n)
581 for (i = 0; i < n; i++) {
582 if (exp1[i] < exp[i])
589 * Update the exponents so that they are the ones the decoder will decode.
591 static void encode_exponents_blk_ch(uint8_t *encoded_exp, uint8_t *exp,
592 int nb_exps, int exp_strategy,
593 uint8_t *num_exp_groups)
595 int group_size, nb_groups, i, j, k, exp_min;
596 uint8_t exp1[AC3_MAX_COEFS];
598 group_size = exp_strategy + (exp_strategy == EXP_D45);
599 *num_exp_groups = (nb_exps + (group_size * 3) - 4) / (3 * group_size);
600 nb_groups = *num_exp_groups * 3;
602 /* for each group, compute the minimum exponent */
603 exp1[0] = exp[0]; /* DC exponent is handled separately */
605 for (i = 1; i <= nb_groups; i++) {
607 assert(exp_min >= 0 && exp_min <= 24);
608 for (j = 1; j < group_size; j++) {
609 if (exp[k+j] < exp_min)
616 /* constraint for DC exponent */
620 /* decrease the delta between each groups to within 2 so that they can be
621 differentially encoded */
622 for (i = 1; i <= nb_groups; i++)
623 exp1[i] = FFMIN(exp1[i], exp1[i-1] + 2);
624 for (i = nb_groups-1; i >= 0; i--)
625 exp1[i] = FFMIN(exp1[i], exp1[i+1] + 2);
627 /* now we have the exponent values the decoder will see */
628 encoded_exp[0] = exp1[0];
630 for (i = 1; i <= nb_groups; i++) {
631 for (j = 0; j < group_size; j++)
632 encoded_exp[k+j] = exp1[i];
639 * Encode exponents from original extracted form to what the decoder will see.
640 * This copies and groups exponents based on exponent strategy and reduces
641 * deltas between adjacent exponent groups so that they can be differentially
644 static void encode_exponents(AC3EncodeContext *s)
646 int blk, blk1, blk2, ch;
647 AC3Block *block, *block1, *block2;
649 for (ch = 0; ch < s->channels; ch++) {
651 block = &s->blocks[0];
652 while (blk < AC3_MAX_BLOCKS) {
655 /* for the EXP_REUSE case we select the min of the exponents */
656 while (blk1 < AC3_MAX_BLOCKS && block1->exp_strategy[ch] == EXP_REUSE) {
657 exponent_min(block->exp[ch], block1->exp[ch], s->nb_coefs[ch]);
661 encode_exponents_blk_ch(block->encoded_exp[ch],
662 block->exp[ch], s->nb_coefs[ch],
663 block->exp_strategy[ch],
664 &block->num_exp_groups[ch]);
665 /* copy encoded exponents for reuse case */
667 for (blk2 = blk+1; blk2 < blk1; blk2++, block2++) {
668 memcpy(block2->encoded_exp[ch], block->encoded_exp[ch],
669 s->nb_coefs[ch] * sizeof(uint8_t));
680 * 3 delta-encoded exponents are in each 7-bit group. The number of groups
681 * varies depending on exponent strategy and bandwidth.
683 static void group_exponents(AC3EncodeContext *s)
686 int group_size, bit_count;
688 int delta0, delta1, delta2;
692 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
693 AC3Block *block = &s->blocks[blk];
694 for (ch = 0; ch < s->channels; ch++) {
695 if (block->exp_strategy[ch] == EXP_REUSE) {
696 block->num_exp_groups[ch] = 0;
699 group_size = block->exp_strategy[ch] + (block->exp_strategy[ch] == EXP_D45);
700 bit_count += 4 + (block->num_exp_groups[ch] * 7);
701 p = block->encoded_exp[ch];
705 block->grouped_exp[ch][0] = exp1;
707 /* remaining exponents are delta encoded */
708 for (i = 1; i <= block->num_exp_groups[ch]; i++) {
709 /* merge three delta in one code */
713 delta0 = exp1 - exp0 + 2;
718 delta1 = exp1 - exp0 + 2;
723 delta2 = exp1 - exp0 + 2;
725 block->grouped_exp[ch][i] = ((delta0 * 5 + delta1) * 5) + delta2;
730 s->exponent_bits = bit_count;
735 * Calculate final exponents from the supplied MDCT coefficients and exponent shift.
736 * Extract exponents from MDCT coefficients, calculate exponent strategies,
737 * and encode final exponents.
739 static void process_exponents(AC3EncodeContext *s)
741 extract_exponents(s);
743 compute_exp_strategy(s);
752 * Initialize bit allocation.
753 * Set default parameter codes and calculate parameter values.
755 static void bit_alloc_init(AC3EncodeContext *s)
759 /* init default parameters */
760 s->slow_decay_code = 2;
761 s->fast_decay_code = 1;
762 s->slow_gain_code = 1;
763 s->db_per_bit_code = 2;
765 for (ch = 0; ch < s->channels; ch++)
766 s->fast_gain_code[ch] = 4;
768 /* initial snr offset */
769 s->coarse_snr_offset = 40;
771 /* compute real values */
772 /* currently none of these values change during encoding, so we can just
773 set them once at initialization */
774 s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->bit_alloc.sr_shift;
775 s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->bit_alloc.sr_shift;
776 s->bit_alloc.slow_gain = ff_ac3_slow_gain_tab[s->slow_gain_code];
777 s->bit_alloc.db_per_bit = ff_ac3_db_per_bit_tab[s->db_per_bit_code];
778 s->bit_alloc.floor = ff_ac3_floor_tab[s->floor_code];
783 * Count the bits used to encode the frame, minus exponents and mantissas.
785 static void count_frame_bits(AC3EncodeContext *s)
787 static const int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };
793 frame_bits += frame_bits_inc[s->channel_mode];
796 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
797 frame_bits += s->fbw_channels * 2 + 2; /* blksw * c, dithflag * c, dynrnge, cplstre */
798 if (s->channel_mode == AC3_CHMODE_STEREO) {
799 frame_bits++; /* rematstr */
803 frame_bits += 2 * s->fbw_channels; /* chexpstr[2] * c */
805 frame_bits++; /* lfeexpstr */
806 for (ch = 0; ch < s->fbw_channels; ch++) {
807 if (s->blocks[blk].exp_strategy[ch] != EXP_REUSE)
808 frame_bits += 6 + 2; /* chbwcod[6], gainrng[2] */
810 frame_bits++; /* baie */
811 frame_bits++; /* snr */
812 frame_bits += 2; /* delta / skip */
814 frame_bits++; /* cplinu for block 0 */
816 /* sdcycod[2], fdcycod[2], sgaincod[2], dbpbcod[2], floorcod[3] */
818 /* (fsnoffset[4] + fgaincod[4]) * c */
819 frame_bits += 2*4 + 3 + 6 + s->channels * (4 + 3);
821 /* auxdatae, crcrsv */
827 s->frame_bits = frame_bits;
832 * Calculate the number of bits needed to encode a set of mantissas.
834 static int compute_mantissa_size(AC3EncodeContext *s, uint8_t *bap, int nb_coefs)
839 for (i = 0; i < nb_coefs; i++) {
843 /* bap=0 mantissas are not encoded */
846 /* 3 mantissas in 5 bits */
847 if (s->mant1_cnt == 0)
849 if (++s->mant1_cnt == 3)
853 /* 3 mantissas in 7 bits */
854 if (s->mant2_cnt == 0)
856 if (++s->mant2_cnt == 3)
863 /* 2 mantissas in 7 bits */
864 if (s->mant4_cnt == 0)
866 if (++s->mant4_cnt == 2)
885 * Calculate masking curve based on the final exponents.
886 * Also calculate the power spectral densities to use in future calculations.
888 static void bit_alloc_masking(AC3EncodeContext *s)
892 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
893 AC3Block *block = &s->blocks[blk];
894 for (ch = 0; ch < s->channels; ch++) {
895 if (block->exp_strategy[ch] == EXP_REUSE) {
896 AC3Block *block1 = &s->blocks[blk-1];
897 memcpy(block->psd[ch], block1->psd[ch], AC3_MAX_COEFS*sizeof(block->psd[0][0]));
898 memcpy(block->mask[ch], block1->mask[ch], AC3_CRITICAL_BANDS*sizeof(block->mask[0][0]));
900 ff_ac3_bit_alloc_calc_psd(block->encoded_exp[ch], 0,
902 block->psd[ch], block->band_psd[ch]);
903 ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, block->band_psd[ch],
905 ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],
906 ch == s->lfe_channel,
907 DBA_NONE, 0, NULL, NULL, NULL,
916 * Run the bit allocation with a given SNR offset.
917 * This calculates the bit allocation pointers that will be used to determine
918 * the quantization of each mantissa.
919 * @return the number of bits needed for mantissas if the given SNR offset is
922 static int bit_alloc(AC3EncodeContext *s,
923 uint8_t bap[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],
929 snr_offset = (snr_offset - 240) << 2;
932 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
933 AC3Block *block = &s->blocks[blk];
937 for (ch = 0; ch < s->channels; ch++) {
938 ff_ac3_bit_alloc_calc_bap(block->mask[ch], block->psd[ch], 0,
939 s->nb_coefs[ch], snr_offset,
940 s->bit_alloc.floor, ff_ac3_bap_tab,
942 mantissa_bits += compute_mantissa_size(s, bap[blk][ch], s->nb_coefs[ch]);
945 return mantissa_bits;
950 * Constant bitrate bit allocation search.
951 * Find the largest SNR offset that will allow data to fit in the frame.
953 static int cbr_bit_allocation(AC3EncodeContext *s)
959 bits_left = 8 * s->frame_size - (s->frame_bits + s->exponent_bits);
961 snr_offset = s->coarse_snr_offset << 4;
963 while (snr_offset >= 0 &&
964 bit_alloc(s, s->bap, snr_offset) > bits_left) {
968 return AVERROR(EINVAL);
970 while (snr_offset + 64 <= 1023 &&
971 bit_alloc(s, s->bap1, snr_offset + 64) <= bits_left) {
973 memcpy(s->bap, s->bap1, sizeof(s->bap1));
975 while (snr_offset + 16 <= 1023 &&
976 bit_alloc(s, s->bap1, snr_offset + 16) <= bits_left) {
978 memcpy(s->bap, s->bap1, sizeof(s->bap1));
980 while (snr_offset + 4 <= 1023 &&
981 bit_alloc(s, s->bap1, snr_offset + 4) <= bits_left) {
983 memcpy(s->bap, s->bap1, sizeof(s->bap1));
985 while (snr_offset + 1 <= 1023 &&
986 bit_alloc(s, s->bap1, snr_offset + 1) <= bits_left) {
988 memcpy(s->bap, s->bap1, sizeof(s->bap1));
991 s->coarse_snr_offset = snr_offset >> 4;
992 for (ch = 0; ch < s->channels; ch++)
993 s->fine_snr_offset[ch] = snr_offset & 0xF;
1000 * Perform bit allocation search.
1001 * Finds the SNR offset value that maximizes quality and fits in the specified
1002 * frame size. Output is the SNR offset and a set of bit allocation pointers
1003 * used to quantize the mantissas.
1005 static int compute_bit_allocation(AC3EncodeContext *s)
1007 count_frame_bits(s);
1009 bit_alloc_masking(s);
1011 return cbr_bit_allocation(s);
1016 * Symmetric quantization on 'levels' levels.
1018 static inline int sym_quant(int c, int e, int levels)
1023 v = (levels * (c << e)) >> 24;
1025 v = (levels >> 1) + v;
1027 v = (levels * ((-c) << e)) >> 24;
1029 v = (levels >> 1) - v;
1031 assert(v >= 0 && v < levels);
1037 * Asymmetric quantization on 2^qbits levels.
1039 static inline int asym_quant(int c, int e, int qbits)
1043 lshift = e + qbits - 24;
1050 m = (1 << (qbits-1));
1054 return v & ((1 << qbits)-1);
1059 * Quantize a set of mantissas for a single channel in a single block.
1061 static void quantize_mantissas_blk_ch(AC3EncodeContext *s,
1062 int32_t *mdct_coef, int8_t exp_shift,
1063 uint8_t *encoded_exp, uint8_t *bap,
1064 uint16_t *qmant, int n)
1068 for (i = 0; i < n; i++) {
1070 int c = mdct_coef[i];
1071 int e = encoded_exp[i] - exp_shift;
1078 v = sym_quant(c, e, 3);
1079 switch (s->mant1_cnt) {
1081 s->qmant1_ptr = &qmant[i];
1086 *s->qmant1_ptr += 3 * v;
1091 *s->qmant1_ptr += v;
1098 v = sym_quant(c, e, 5);
1099 switch (s->mant2_cnt) {
1101 s->qmant2_ptr = &qmant[i];
1106 *s->qmant2_ptr += 5 * v;
1111 *s->qmant2_ptr += v;
1118 v = sym_quant(c, e, 7);
1121 v = sym_quant(c, e, 11);
1122 switch (s->mant4_cnt) {
1124 s->qmant4_ptr = &qmant[i];
1129 *s->qmant4_ptr += v;
1136 v = sym_quant(c, e, 15);
1139 v = asym_quant(c, e, 14);
1142 v = asym_quant(c, e, 16);
1145 v = asym_quant(c, e, b - 1);
1154 * Quantize mantissas using coefficients, exponents, and bit allocation pointers.
1156 static void quantize_mantissas(AC3EncodeContext *s)
1161 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
1162 AC3Block *block = &s->blocks[blk];
1163 s->mant1_cnt = s->mant2_cnt = s->mant4_cnt = 0;
1164 s->qmant1_ptr = s->qmant2_ptr = s->qmant4_ptr = NULL;
1166 for (ch = 0; ch < s->channels; ch++) {
1167 quantize_mantissas_blk_ch(s, block->mdct_coef[ch], block->exp_shift[ch],
1168 block->encoded_exp[ch], s->bap[blk][ch],
1169 block->qmant[ch], s->nb_coefs[ch]);
1176 * Write the AC-3 frame header to the output bitstream.
1178 static void output_frame_header(AC3EncodeContext *s)
1180 put_bits(&s->pb, 16, 0x0b77); /* frame header */
1181 put_bits(&s->pb, 16, 0); /* crc1: will be filled later */
1182 put_bits(&s->pb, 2, s->bit_alloc.sr_code);
1183 put_bits(&s->pb, 6, s->frame_size_code + (s->frame_size - s->frame_size_min) / 2);
1184 put_bits(&s->pb, 5, s->bitstream_id);
1185 put_bits(&s->pb, 3, s->bitstream_mode);
1186 put_bits(&s->pb, 3, s->channel_mode);
1187 if ((s->channel_mode & 0x01) && s->channel_mode != AC3_CHMODE_MONO)
1188 put_bits(&s->pb, 2, 1); /* XXX -4.5 dB */
1189 if (s->channel_mode & 0x04)
1190 put_bits(&s->pb, 2, 1); /* XXX -6 dB */
1191 if (s->channel_mode == AC3_CHMODE_STEREO)
1192 put_bits(&s->pb, 2, 0); /* surround not indicated */
1193 put_bits(&s->pb, 1, s->lfe_on); /* LFE */
1194 put_bits(&s->pb, 5, 31); /* dialog norm: -31 db */
1195 put_bits(&s->pb, 1, 0); /* no compression control word */
1196 put_bits(&s->pb, 1, 0); /* no lang code */
1197 put_bits(&s->pb, 1, 0); /* no audio production info */
1198 put_bits(&s->pb, 1, 0); /* no copyright */
1199 put_bits(&s->pb, 1, 1); /* original bitstream */
1200 put_bits(&s->pb, 1, 0); /* no time code 1 */
1201 put_bits(&s->pb, 1, 0); /* no time code 2 */
1202 put_bits(&s->pb, 1, 0); /* no additional bit stream info */
1207 * Write one audio block to the output bitstream.
1209 static void output_audio_block(AC3EncodeContext *s,
1212 int ch, i, baie, rbnd;
1213 AC3Block *block = &s->blocks[block_num];
1215 /* block switching */
1216 for (ch = 0; ch < s->fbw_channels; ch++)
1217 put_bits(&s->pb, 1, 0);
1220 for (ch = 0; ch < s->fbw_channels; ch++)
1221 put_bits(&s->pb, 1, 1);
1223 /* dynamic range codes */
1224 put_bits(&s->pb, 1, 0);
1226 /* channel coupling */
1228 put_bits(&s->pb, 1, 1); /* coupling strategy present */
1229 put_bits(&s->pb, 1, 0); /* no coupling strategy */
1231 put_bits(&s->pb, 1, 0); /* no new coupling strategy */
1234 /* stereo rematrixing */
1235 if (s->channel_mode == AC3_CHMODE_STEREO) {
1237 /* first block must define rematrixing (rematstr) */
1238 put_bits(&s->pb, 1, 1);
1240 /* dummy rematrixing rematflg(1:4)=0 */
1241 for (rbnd = 0; rbnd < 4; rbnd++)
1242 put_bits(&s->pb, 1, 0);
1244 /* no matrixing (but should be used in the future) */
1245 put_bits(&s->pb, 1, 0);
1249 /* exponent strategy */
1250 for (ch = 0; ch < s->fbw_channels; ch++)
1251 put_bits(&s->pb, 2, block->exp_strategy[ch]);
1253 put_bits(&s->pb, 1, block->exp_strategy[s->lfe_channel]);
1256 for (ch = 0; ch < s->fbw_channels; ch++) {
1257 if (block->exp_strategy[ch] != EXP_REUSE)
1258 put_bits(&s->pb, 6, s->bandwidth_code[ch]);
1262 for (ch = 0; ch < s->channels; ch++) {
1263 if (block->exp_strategy[ch] == EXP_REUSE)
1267 put_bits(&s->pb, 4, block->grouped_exp[ch][0]);
1269 /* exponent groups */
1270 for (i = 1; i <= block->num_exp_groups[ch]; i++)
1271 put_bits(&s->pb, 7, block->grouped_exp[ch][i]);
1273 /* gain range info */
1274 if (ch != s->lfe_channel)
1275 put_bits(&s->pb, 2, 0);
1278 /* bit allocation info */
1279 baie = (block_num == 0);
1280 put_bits(&s->pb, 1, baie);
1282 put_bits(&s->pb, 2, s->slow_decay_code);
1283 put_bits(&s->pb, 2, s->fast_decay_code);
1284 put_bits(&s->pb, 2, s->slow_gain_code);
1285 put_bits(&s->pb, 2, s->db_per_bit_code);
1286 put_bits(&s->pb, 3, s->floor_code);
1290 put_bits(&s->pb, 1, baie);
1292 put_bits(&s->pb, 6, s->coarse_snr_offset);
1293 for (ch = 0; ch < s->channels; ch++) {
1294 put_bits(&s->pb, 4, s->fine_snr_offset[ch]);
1295 put_bits(&s->pb, 3, s->fast_gain_code[ch]);
1299 put_bits(&s->pb, 1, 0); /* no delta bit allocation */
1300 put_bits(&s->pb, 1, 0); /* no data to skip */
1303 for (ch = 0; ch < s->channels; ch++) {
1305 for (i = 0; i < s->nb_coefs[ch]; i++) {
1306 q = block->qmant[ch][i];
1307 b = s->bap[block_num][ch][i];
1310 case 1: if (q != 128) put_bits(&s->pb, 5, q); break;
1311 case 2: if (q != 128) put_bits(&s->pb, 7, q); break;
1312 case 3: put_bits(&s->pb, 3, q); break;
1313 case 4: if (q != 128) put_bits(&s->pb, 7, q); break;
1314 case 14: put_bits(&s->pb, 14, q); break;
1315 case 15: put_bits(&s->pb, 16, q); break;
1316 default: put_bits(&s->pb, b-1, q); break;
1323 /** CRC-16 Polynomial */
1324 #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))
1327 static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)
1344 static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)
1350 r = mul_poly(r, a, poly);
1351 a = mul_poly(a, a, poly);
1359 * Fill the end of the frame with 0's and compute the two CRCs.
1361 static void output_frame_end(AC3EncodeContext *s)
1363 int frame_size, frame_size_58, pad_bytes, crc1, crc2, crc_inv;
1366 frame_size = s->frame_size;
1367 frame_size_58 = ((frame_size >> 2) + (frame_size >> 4)) << 1;
1369 /* pad the remainder of the frame with zeros */
1370 flush_put_bits(&s->pb);
1372 pad_bytes = s->frame_size - (put_bits_ptr(&s->pb) - frame) - 2;
1373 assert(pad_bytes >= 0);
1375 memset(put_bits_ptr(&s->pb), 0, pad_bytes);
1378 /* this is not so easy because it is at the beginning of the data... */
1379 crc1 = av_bswap16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,
1380 frame + 4, frame_size_58 - 4));
1381 /* XXX: could precompute crc_inv */
1382 crc_inv = pow_poly((CRC16_POLY >> 1), (8 * frame_size_58) - 16, CRC16_POLY);
1383 crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);
1384 AV_WB16(frame + 2, crc1);
1387 crc2 = av_bswap16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,
1388 frame + frame_size_58,
1389 frame_size - frame_size_58 - 2));
1390 AV_WB16(frame + frame_size - 2, crc2);
1395 * Write the frame to the output bitstream.
1397 static void output_frame(AC3EncodeContext *s,
1398 unsigned char *frame)
1402 init_put_bits(&s->pb, frame, AC3_MAX_CODED_FRAME_SIZE);
1404 output_frame_header(s);
1406 for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
1407 output_audio_block(s, blk);
1409 output_frame_end(s);
1414 * Encode a single AC-3 frame.
1416 static int ac3_encode_frame(AVCodecContext *avctx,
1417 unsigned char *frame, int buf_size, void *data)
1419 AC3EncodeContext *s = avctx->priv_data;
1420 const int16_t *samples = data;
1423 if (s->bit_alloc.sr_code == 1)
1424 adjust_frame_size(s);
1426 deinterleave_input_samples(s, samples);
1430 process_exponents(s);
1432 ret = compute_bit_allocation(s);
1434 av_log(avctx, AV_LOG_ERROR, "Bit allocation failed. Try increasing the bitrate.\n");
1438 quantize_mantissas(s);
1440 output_frame(s, frame);
1442 return s->frame_size;
1447 * Finalize encoding and free any memory allocated by the encoder.
1449 static av_cold int ac3_encode_close(AVCodecContext *avctx)
1451 av_freep(&avctx->coded_frame);
1457 * Set channel information during initialization.
1459 static av_cold int set_channel_info(AC3EncodeContext *s, int channels,
1460 int64_t *channel_layout)
1464 if (channels < 1 || channels > AC3_MAX_CHANNELS)
1465 return AVERROR(EINVAL);
1466 if ((uint64_t)*channel_layout > 0x7FF)
1467 return AVERROR(EINVAL);
1468 ch_layout = *channel_layout;
1470 ch_layout = avcodec_guess_channel_layout(channels, CODEC_ID_AC3, NULL);
1471 if (av_get_channel_layout_nb_channels(ch_layout) != channels)
1472 return AVERROR(EINVAL);
1474 s->lfe_on = !!(ch_layout & AV_CH_LOW_FREQUENCY);
1475 s->channels = channels;
1476 s->fbw_channels = channels - s->lfe_on;
1477 s->lfe_channel = s->lfe_on ? s->fbw_channels : -1;
1479 ch_layout -= AV_CH_LOW_FREQUENCY;
1481 switch (ch_layout) {
1482 case AV_CH_LAYOUT_MONO: s->channel_mode = AC3_CHMODE_MONO; break;
1483 case AV_CH_LAYOUT_STEREO: s->channel_mode = AC3_CHMODE_STEREO; break;
1484 case AV_CH_LAYOUT_SURROUND: s->channel_mode = AC3_CHMODE_3F; break;
1485 case AV_CH_LAYOUT_2_1: s->channel_mode = AC3_CHMODE_2F1R; break;
1486 case AV_CH_LAYOUT_4POINT0: s->channel_mode = AC3_CHMODE_3F1R; break;
1487 case AV_CH_LAYOUT_QUAD:
1488 case AV_CH_LAYOUT_2_2: s->channel_mode = AC3_CHMODE_2F2R; break;
1489 case AV_CH_LAYOUT_5POINT0:
1490 case AV_CH_LAYOUT_5POINT0_BACK: s->channel_mode = AC3_CHMODE_3F2R; break;
1492 return AVERROR(EINVAL);
1495 s->channel_map = ff_ac3_enc_channel_map[s->channel_mode][s->lfe_on];
1496 *channel_layout = ch_layout;
1498 *channel_layout |= AV_CH_LOW_FREQUENCY;
1504 static av_cold int validate_options(AVCodecContext *avctx, AC3EncodeContext *s)
1508 /* validate channel layout */
1509 if (!avctx->channel_layout) {
1510 av_log(avctx, AV_LOG_WARNING, "No channel layout specified. The "
1511 "encoder will guess the layout, but it "
1512 "might be incorrect.\n");
1514 ret = set_channel_info(s, avctx->channels, &avctx->channel_layout);
1516 av_log(avctx, AV_LOG_ERROR, "invalid channel layout\n");
1520 /* validate sample rate */
1521 for (i = 0; i < 9; i++) {
1522 if ((ff_ac3_sample_rate_tab[i / 3] >> (i % 3)) == avctx->sample_rate)
1526 av_log(avctx, AV_LOG_ERROR, "invalid sample rate\n");
1527 return AVERROR(EINVAL);
1529 s->sample_rate = avctx->sample_rate;
1530 s->bit_alloc.sr_shift = i % 3;
1531 s->bit_alloc.sr_code = i / 3;
1533 /* validate bit rate */
1534 for (i = 0; i < 19; i++) {
1535 if ((ff_ac3_bitrate_tab[i] >> s->bit_alloc.sr_shift)*1000 == avctx->bit_rate)
1539 av_log(avctx, AV_LOG_ERROR, "invalid bit rate\n");
1540 return AVERROR(EINVAL);
1542 s->bit_rate = avctx->bit_rate;
1543 s->frame_size_code = i << 1;
1550 * Set bandwidth for all channels.
1551 * The user can optionally supply a cutoff frequency. Otherwise an appropriate
1552 * default value will be used.
1554 static av_cold void set_bandwidth(AC3EncodeContext *s, int cutoff)
1559 /* calculate bandwidth based on user-specified cutoff frequency */
1561 cutoff = av_clip(cutoff, 1, s->sample_rate >> 1);
1562 fbw_coeffs = cutoff * 2 * AC3_MAX_COEFS / s->sample_rate;
1563 bw_code = av_clip((fbw_coeffs - 73) / 3, 0, 60);
1565 /* use default bandwidth setting */
1566 /* XXX: should compute the bandwidth according to the frame
1567 size, so that we avoid annoying high frequency artifacts */
1571 /* set number of coefficients for each channel */
1572 for (ch = 0; ch < s->fbw_channels; ch++) {
1573 s->bandwidth_code[ch] = bw_code;
1574 s->nb_coefs[ch] = bw_code * 3 + 73;
1577 s->nb_coefs[s->lfe_channel] = 7; /* LFE channel always has 7 coefs */
1582 * Initialize the encoder.
1584 static av_cold int ac3_encode_init(AVCodecContext *avctx)
1586 AC3EncodeContext *s = avctx->priv_data;
1589 avctx->frame_size = AC3_FRAME_SIZE;
1593 ret = validate_options(avctx, s);
1597 s->bitstream_id = 8 + s->bit_alloc.sr_shift;
1598 s->bitstream_mode = 0; /* complete main audio service */
1600 s->frame_size_min = 2 * ff_ac3_frame_size_tab[s->frame_size_code][s->bit_alloc.sr_code];
1601 s->bits_written = 0;
1602 s->samples_written = 0;
1603 s->frame_size = s->frame_size_min;
1605 set_bandwidth(s, avctx->cutoff);
1611 avctx->coded_frame= avcodec_alloc_frame();
1612 avctx->coded_frame->key_frame= 1;
1619 /*************************************************************************/
1622 #include "libavutil/lfg.h"
1624 #define FN (MDCT_SAMPLES/4)
1627 static void fft_test(AVLFG *lfg)
1629 IComplex in[FN], in1[FN];
1631 float sum_re, sum_im, a;
1633 for (i = 0; i < FN; i++) {
1634 in[i].re = av_lfg_get(lfg) % 65535 - 32767;
1635 in[i].im = av_lfg_get(lfg) % 65535 - 32767;
1641 for (k = 0; k < FN; k++) {
1644 for (n = 0; n < FN; n++) {
1645 a = -2 * M_PI * (n * k) / FN;
1646 sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);
1647 sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);
1649 av_log(NULL, AV_LOG_DEBUG, "%3d: %6d,%6d %6.0f,%6.0f\n",
1650 k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);
1655 static void mdct_test(AVLFG *lfg)
1657 int16_t input[MDCT_SAMPLES];
1658 int32_t output[AC3_MAX_COEFS];
1659 float input1[MDCT_SAMPLES];
1660 float output1[AC3_MAX_COEFS];
1661 float s, a, err, e, emax;
1664 for (i = 0; i < MDCT_SAMPLES; i++) {
1665 input[i] = (av_lfg_get(lfg) % 65535 - 32767) * 9 / 10;
1666 input1[i] = input[i];
1669 mdct512(output, input);
1672 for (k = 0; k < AC3_MAX_COEFS; k++) {
1674 for (n = 0; n < MDCT_SAMPLES; n++) {
1675 a = (2*M_PI*(2*n+1+MDCT_SAMPLES/2)*(2*k+1) / (4 * MDCT_SAMPLES));
1676 s += input1[n] * cos(a);
1678 output1[k] = -2 * s / MDCT_SAMPLES;
1683 for (i = 0; i < AC3_MAX_COEFS; i++) {
1684 av_log(NULL, AV_LOG_DEBUG, "%3d: %7d %7.0f\n", i, output[i], output1[i]);
1685 e = output[i] - output1[i];
1690 av_log(NULL, AV_LOG_DEBUG, "err2=%f emax=%f\n", err / AC3_MAX_COEFS, emax);
1698 av_log_set_level(AV_LOG_DEBUG);
1709 AVCodec ac3_encoder = {
1713 sizeof(AC3EncodeContext),
1718 .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
1719 .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
1720 .channel_layouts = (const int64_t[]){
1722 AV_CH_LAYOUT_STEREO,
1724 AV_CH_LAYOUT_SURROUND,
1727 AV_CH_LAYOUT_4POINT0,
1728 AV_CH_LAYOUT_5POINT0,
1729 AV_CH_LAYOUT_5POINT0_BACK,
1730 (AV_CH_LAYOUT_MONO | AV_CH_LOW_FREQUENCY),
1731 (AV_CH_LAYOUT_STEREO | AV_CH_LOW_FREQUENCY),
1732 (AV_CH_LAYOUT_2_1 | AV_CH_LOW_FREQUENCY),
1733 (AV_CH_LAYOUT_SURROUND | AV_CH_LOW_FREQUENCY),
1734 (AV_CH_LAYOUT_2_2 | AV_CH_LOW_FREQUENCY),
1735 (AV_CH_LAYOUT_QUAD | AV_CH_LOW_FREQUENCY),
1736 (AV_CH_LAYOUT_4POINT0 | AV_CH_LOW_FREQUENCY),
1737 AV_CH_LAYOUT_5POINT1,
1738 AV_CH_LAYOUT_5POINT1_BACK,