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
23 * @file libavcodec/ac3enc.c
24 * The simplest AC-3 encoder.
27 //#define DEBUG_BITALLOC
28 #include "libavutil/crc.h"
30 #include "bitstream.h"
33 typedef struct AC3EncodeContext {
39 unsigned int sample_rate;
40 unsigned int bitstream_id;
41 unsigned int frame_size_min; /* minimum frame size in case rounding is necessary */
42 unsigned int frame_size; /* current frame size in words */
43 unsigned int bits_written;
44 unsigned int samples_written;
46 unsigned int frame_size_code;
47 unsigned int sr_code; /* frequency */
48 unsigned int channel_mode;
50 unsigned int bitstream_mode;
51 short last_samples[AC3_MAX_CHANNELS][256];
52 unsigned int chbwcod[AC3_MAX_CHANNELS];
53 int nb_coefs[AC3_MAX_CHANNELS];
55 /* bitrate allocation control */
56 int slow_gain_code, slow_decay_code, fast_decay_code, db_per_bit_code, floor_code;
57 AC3BitAllocParameters bit_alloc;
58 int coarse_snr_offset;
59 int fast_gain_code[AC3_MAX_CHANNELS];
60 int fine_snr_offset[AC3_MAX_CHANNELS];
61 /* mantissa encoding */
62 int mant1_cnt, mant2_cnt, mant4_cnt;
65 static int16_t costab[64];
66 static int16_t sintab[64];
67 static int16_t xcos1[128];
68 static int16_t xsin1[128];
71 #define N (1 << MDCT_NBITS)
73 /* new exponents are sent if their Norm 1 exceed this number */
74 #define EXP_DIFF_THRESHOLD 1000
76 static inline int16_t fix15(float a)
79 v = (int)(a * (float)(1 << 15));
87 typedef struct IComplex {
91 static av_cold void fft_init(int ln)
98 for(i=0;i<(n/2);i++) {
99 alpha = 2 * M_PI * (float)i / (float)n;
100 costab[i] = fix15(cos(alpha));
101 sintab[i] = fix15(sin(alpha));
106 #define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1) \
113 pre = (bx + ax) >> 1;\
114 pim = (by + ay) >> 1;\
115 qre = (bx - ax) >> 1;\
116 qim = (by - ay) >> 1;\
119 #define CMUL(pre, pim, are, aim, bre, bim) \
121 pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15;\
122 pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15;\
126 /* do a 2^n point complex fft on 2^ln points. */
127 static void fft(IComplex *z, int ln)
131 register IComplex *p,*q;
138 int k = ff_reverse[j] >> (8 - ln);
140 FFSWAP(IComplex, z[k], z[j]);
148 BF(p[0].re, p[0].im, p[1].re, p[1].im,
149 p[0].re, p[0].im, p[1].re, p[1].im);
158 BF(p[0].re, p[0].im, p[2].re, p[2].im,
159 p[0].re, p[0].im, p[2].re, p[2].im);
160 BF(p[1].re, p[1].im, p[3].re, p[3].im,
161 p[1].re, p[1].im, p[3].im, -p[3].re);
173 for (j = 0; j < nblocks; ++j) {
175 BF(p->re, p->im, q->re, q->im,
176 p->re, p->im, q->re, q->im);
180 for(l = nblocks; l < np2; l += nblocks) {
181 CMUL(tmp_re, tmp_im, costab[l], -sintab[l], q->re, q->im);
182 BF(p->re, p->im, q->re, q->im,
183 p->re, p->im, tmp_re, tmp_im);
190 nblocks = nblocks >> 1;
191 nloops = nloops << 1;
192 } while (nblocks != 0);
195 /* do a 512 point mdct */
196 static void mdct512(int32_t *out, int16_t *in)
198 int i, re, im, re1, im1;
202 /* shift to simplify computations */
204 rot[i] = -in[i + 3*N/4];
206 rot[i] = in[i - N/4];
210 re = ((int)rot[2*i] - (int)rot[N-1-2*i]) >> 1;
211 im = -((int)rot[N/2+2*i] - (int)rot[N/2-1-2*i]) >> 1;
212 CMUL(x[i].re, x[i].im, re, im, -xcos1[i], xsin1[i]);
215 fft(x, MDCT_NBITS - 2);
221 CMUL(re1, im1, re, im, xsin1[i], xcos1[i]);
223 out[N/2-1-2*i] = re1;
227 /* XXX: use another norm ? */
228 static int calc_exp_diff(uint8_t *exp1, uint8_t *exp2, int n)
233 sum += abs(exp1[i] - exp2[i]);
238 static void compute_exp_strategy(uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
239 uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
245 /* estimate if the exponent variation & decide if they should be
246 reused in the next frame */
247 exp_strategy[0][ch] = EXP_NEW;
248 for(i=1;i<NB_BLOCKS;i++) {
249 exp_diff = calc_exp_diff(exp[i][ch], exp[i-1][ch], N/2);
251 av_log(NULL, AV_LOG_DEBUG, "exp_diff=%d\n", exp_diff);
253 if (exp_diff > EXP_DIFF_THRESHOLD)
254 exp_strategy[i][ch] = EXP_NEW;
256 exp_strategy[i][ch] = EXP_REUSE;
261 /* now select the encoding strategy type : if exponents are often
262 recoded, we use a coarse encoding */
264 while (i < NB_BLOCKS) {
266 while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE)
270 exp_strategy[i][ch] = EXP_D45;
274 exp_strategy[i][ch] = EXP_D25;
277 exp_strategy[i][ch] = EXP_D15;
284 /* set exp[i] to min(exp[i], exp1[i]) */
285 static void exponent_min(uint8_t exp[N/2], uint8_t exp1[N/2], int n)
290 if (exp1[i] < exp[i])
295 /* update the exponents so that they are the ones the decoder will
296 decode. Return the number of bits used to code the exponents */
297 static int encode_exp(uint8_t encoded_exp[N/2],
302 int group_size, nb_groups, i, j, k, exp_min;
305 switch(exp_strategy) {
317 nb_groups = ((nb_exps + (group_size * 3) - 4) / (3 * group_size)) * 3;
319 /* for each group, compute the minimum exponent */
320 exp1[0] = exp[0]; /* DC exponent is handled separately */
322 for(i=1;i<=nb_groups;i++) {
324 assert(exp_min >= 0 && exp_min <= 24);
325 for(j=1;j<group_size;j++) {
326 if (exp[k+j] < exp_min)
333 /* constraint for DC exponent */
337 /* Decrease the delta between each groups to within 2
338 * so that they can be differentially encoded */
339 for (i=1;i<=nb_groups;i++)
340 exp1[i] = FFMIN(exp1[i], exp1[i-1] + 2);
341 for (i=nb_groups-1;i>=0;i--)
342 exp1[i] = FFMIN(exp1[i], exp1[i+1] + 2);
344 /* now we have the exponent values the decoder will see */
345 encoded_exp[0] = exp1[0];
347 for(i=1;i<=nb_groups;i++) {
348 for(j=0;j<group_size;j++) {
349 encoded_exp[k+j] = exp1[i];
355 av_log(NULL, AV_LOG_DEBUG, "exponents: strategy=%d\n", exp_strategy);
356 for(i=0;i<=nb_groups * group_size;i++) {
357 av_log(NULL, AV_LOG_DEBUG, "%d ", encoded_exp[i]);
359 av_log(NULL, AV_LOG_DEBUG, "\n");
362 return 4 + (nb_groups / 3) * 7;
365 /* return the size in bits taken by the mantissa */
366 static int compute_mantissa_size(AC3EncodeContext *s, uint8_t *m, int nb_coefs)
371 for(i=0;i<nb_coefs;i++) {
378 /* 3 mantissa in 5 bits */
379 if (s->mant1_cnt == 0)
381 if (++s->mant1_cnt == 3)
385 /* 3 mantissa in 7 bits */
386 if (s->mant2_cnt == 0)
388 if (++s->mant2_cnt == 3)
395 /* 2 mantissa in 7 bits */
396 if (s->mant4_cnt == 0)
398 if (++s->mant4_cnt == 2)
416 static void bit_alloc_masking(AC3EncodeContext *s,
417 uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
418 uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
419 int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
420 int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50])
423 int16_t band_psd[NB_BLOCKS][AC3_MAX_CHANNELS][50];
425 for(blk=0; blk<NB_BLOCKS; blk++) {
426 for(ch=0;ch<s->nb_all_channels;ch++) {
427 if(exp_strategy[blk][ch] == EXP_REUSE) {
428 memcpy(psd[blk][ch], psd[blk-1][ch], (N/2)*sizeof(int16_t));
429 memcpy(mask[blk][ch], mask[blk-1][ch], 50*sizeof(int16_t));
431 ff_ac3_bit_alloc_calc_psd(encoded_exp[blk][ch], 0,
433 psd[blk][ch], band_psd[blk][ch]);
434 ff_ac3_bit_alloc_calc_mask(&s->bit_alloc, band_psd[blk][ch],
436 ff_ac3_fast_gain_tab[s->fast_gain_code[ch]],
437 ch == s->lfe_channel,
438 DBA_NONE, 0, NULL, NULL, NULL,
445 static int bit_alloc(AC3EncodeContext *s,
446 int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50],
447 int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
448 uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
449 int frame_bits, int coarse_snr_offset, int fine_snr_offset)
454 snr_offset = (((coarse_snr_offset - 15) << 4) + fine_snr_offset) << 2;
457 for(i=0;i<NB_BLOCKS;i++) {
461 for(ch=0;ch<s->nb_all_channels;ch++) {
462 ff_ac3_bit_alloc_calc_bap(mask[i][ch], psd[i][ch], 0,
463 s->nb_coefs[ch], snr_offset,
464 s->bit_alloc.floor, ff_ac3_bap_tab,
466 frame_bits += compute_mantissa_size(s, bap[i][ch],
471 printf("csnr=%d fsnr=%d frame_bits=%d diff=%d\n",
472 coarse_snr_offset, fine_snr_offset, frame_bits,
473 16 * s->frame_size - ((frame_bits + 7) & ~7));
475 return 16 * s->frame_size - frame_bits;
480 static int compute_bit_allocation(AC3EncodeContext *s,
481 uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
482 uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2],
483 uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS],
487 int coarse_snr_offset, fine_snr_offset;
488 uint8_t bap1[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
489 int16_t psd[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
490 int16_t mask[NB_BLOCKS][AC3_MAX_CHANNELS][50];
491 static const int frame_bits_inc[8] = { 0, 0, 2, 2, 2, 4, 2, 4 };
493 /* init default parameters */
494 s->slow_decay_code = 2;
495 s->fast_decay_code = 1;
496 s->slow_gain_code = 1;
497 s->db_per_bit_code = 2;
499 for(ch=0;ch<s->nb_all_channels;ch++)
500 s->fast_gain_code[ch] = 4;
502 /* compute real values */
503 s->bit_alloc.sr_code = s->sr_code;
504 s->bit_alloc.sr_shift = s->sr_shift;
505 s->bit_alloc.slow_decay = ff_ac3_slow_decay_tab[s->slow_decay_code] >> s->sr_shift;
506 s->bit_alloc.fast_decay = ff_ac3_fast_decay_tab[s->fast_decay_code] >> s->sr_shift;
507 s->bit_alloc.slow_gain = ff_ac3_slow_gain_tab[s->slow_gain_code];
508 s->bit_alloc.db_per_bit = ff_ac3_db_per_bit_tab[s->db_per_bit_code];
509 s->bit_alloc.floor = ff_ac3_floor_tab[s->floor_code];
513 // if (s->channel_mode == 2)
515 frame_bits += frame_bits_inc[s->channel_mode];
518 for(i=0;i<NB_BLOCKS;i++) {
519 frame_bits += s->nb_channels * 2 + 2; /* blksw * c, dithflag * c, dynrnge, cplstre */
520 if (s->channel_mode == AC3_CHMODE_STEREO) {
521 frame_bits++; /* rematstr */
522 if(i==0) frame_bits += 4;
524 frame_bits += 2 * s->nb_channels; /* chexpstr[2] * c */
526 frame_bits++; /* lfeexpstr */
527 for(ch=0;ch<s->nb_channels;ch++) {
528 if (exp_strategy[i][ch] != EXP_REUSE)
529 frame_bits += 6 + 2; /* chbwcod[6], gainrng[2] */
531 frame_bits++; /* baie */
532 frame_bits++; /* snr */
533 frame_bits += 2; /* delta / skip */
535 frame_bits++; /* cplinu for block 0 */
537 /* sdcycod[2], fdcycod[2], sgaincod[2], dbpbcod[2], floorcod[3] */
539 /* (fsnoffset[4] + fgaincod[4]) * c */
540 frame_bits += 2*4 + 3 + 6 + s->nb_all_channels * (4 + 3);
542 /* auxdatae, crcrsv */
548 /* calculate psd and masking curve before doing bit allocation */
549 bit_alloc_masking(s, encoded_exp, exp_strategy, psd, mask);
551 /* now the big work begins : do the bit allocation. Modify the snr
552 offset until we can pack everything in the requested frame size */
554 coarse_snr_offset = s->coarse_snr_offset;
555 while (coarse_snr_offset >= 0 &&
556 bit_alloc(s, mask, psd, bap, frame_bits, coarse_snr_offset, 0) < 0)
557 coarse_snr_offset -= SNR_INC1;
558 if (coarse_snr_offset < 0) {
559 av_log(NULL, AV_LOG_ERROR, "Bit allocation failed. Try increasing the bitrate.\n");
562 while ((coarse_snr_offset + SNR_INC1) <= 63 &&
563 bit_alloc(s, mask, psd, bap1, frame_bits,
564 coarse_snr_offset + SNR_INC1, 0) >= 0) {
565 coarse_snr_offset += SNR_INC1;
566 memcpy(bap, bap1, sizeof(bap1));
568 while ((coarse_snr_offset + 1) <= 63 &&
569 bit_alloc(s, mask, psd, bap1, frame_bits, coarse_snr_offset + 1, 0) >= 0) {
571 memcpy(bap, bap1, sizeof(bap1));
575 while ((fine_snr_offset + SNR_INC1) <= 15 &&
576 bit_alloc(s, mask, psd, bap1, frame_bits,
577 coarse_snr_offset, fine_snr_offset + SNR_INC1) >= 0) {
578 fine_snr_offset += SNR_INC1;
579 memcpy(bap, bap1, sizeof(bap1));
581 while ((fine_snr_offset + 1) <= 15 &&
582 bit_alloc(s, mask, psd, bap1, frame_bits,
583 coarse_snr_offset, fine_snr_offset + 1) >= 0) {
585 memcpy(bap, bap1, sizeof(bap1));
588 s->coarse_snr_offset = coarse_snr_offset;
589 for(ch=0;ch<s->nb_all_channels;ch++)
590 s->fine_snr_offset[ch] = fine_snr_offset;
591 #if defined(DEBUG_BITALLOC)
596 for(ch=0;ch<s->nb_all_channels;ch++) {
597 printf("Block #%d Ch%d:\n", i, ch);
599 for(j=0;j<s->nb_coefs[ch];j++) {
600 printf("%d ",bap[i][ch][j]);
610 static av_cold int AC3_encode_init(AVCodecContext *avctx)
612 int freq = avctx->sample_rate;
613 int bitrate = avctx->bit_rate;
614 int channels = avctx->channels;
615 AC3EncodeContext *s = avctx->priv_data;
619 static const uint8_t channel_mode_defs[6] = {
623 0x06, /* L R SL SR */
624 0x07, /* L C R SL SR */
625 0x07, /* L C R SL SR (+LFE) */
628 avctx->frame_size = AC3_FRAME_SIZE;
632 /* number of channels */
633 if (channels < 1 || channels > 6)
635 s->channel_mode = channel_mode_defs[channels - 1];
636 s->lfe = (channels == 6) ? 1 : 0;
637 s->nb_all_channels = channels;
638 s->nb_channels = channels > 5 ? 5 : channels;
639 s->lfe_channel = s->lfe ? 5 : -1;
644 if ((ff_ac3_sample_rate_tab[j] >> i) == freq)
649 s->sample_rate = freq;
652 s->bitstream_id = 8 + s->sr_shift;
653 s->bitstream_mode = 0; /* complete main audio service */
655 /* bitrate & frame size */
657 if ((ff_ac3_bitrate_tab[i] >> s->sr_shift)*1000 == bitrate)
662 s->bit_rate = bitrate;
663 s->frame_size_code = i << 1;
664 s->frame_size_min = ff_ac3_frame_size_tab[s->frame_size_code][s->sr_code];
666 s->samples_written = 0;
667 s->frame_size = s->frame_size_min;
669 /* bit allocation init */
671 /* calculate bandwidth based on user-specified cutoff frequency */
672 int cutoff = av_clip(avctx->cutoff, 1, s->sample_rate >> 1);
673 int fbw_coeffs = cutoff * 512 / s->sample_rate;
674 bw_code = av_clip((fbw_coeffs - 73) / 3, 0, 60);
676 /* use default bandwidth setting */
677 /* XXX: should compute the bandwidth according to the frame
678 size, so that we avoid annoying high frequency artifacts */
681 for(ch=0;ch<s->nb_channels;ch++) {
682 /* bandwidth for each channel */
683 s->chbwcod[ch] = bw_code;
684 s->nb_coefs[ch] = bw_code * 3 + 73;
687 s->nb_coefs[s->lfe_channel] = 7; /* fixed */
689 /* initial snr offset */
690 s->coarse_snr_offset = 40;
693 fft_init(MDCT_NBITS - 2);
695 alpha = 2 * M_PI * (i + 1.0 / 8.0) / (float)N;
696 xcos1[i] = fix15(-cos(alpha));
697 xsin1[i] = fix15(-sin(alpha));
700 avctx->coded_frame= avcodec_alloc_frame();
701 avctx->coded_frame->key_frame= 1;
706 /* output the AC-3 frame header */
707 static void output_frame_header(AC3EncodeContext *s, unsigned char *frame)
709 init_put_bits(&s->pb, frame, AC3_MAX_CODED_FRAME_SIZE);
711 put_bits(&s->pb, 16, 0x0b77); /* frame header */
712 put_bits(&s->pb, 16, 0); /* crc1: will be filled later */
713 put_bits(&s->pb, 2, s->sr_code);
714 put_bits(&s->pb, 6, s->frame_size_code + (s->frame_size - s->frame_size_min));
715 put_bits(&s->pb, 5, s->bitstream_id);
716 put_bits(&s->pb, 3, s->bitstream_mode);
717 put_bits(&s->pb, 3, s->channel_mode);
718 if ((s->channel_mode & 0x01) && s->channel_mode != AC3_CHMODE_MONO)
719 put_bits(&s->pb, 2, 1); /* XXX -4.5 dB */
720 if (s->channel_mode & 0x04)
721 put_bits(&s->pb, 2, 1); /* XXX -6 dB */
722 if (s->channel_mode == AC3_CHMODE_STEREO)
723 put_bits(&s->pb, 2, 0); /* surround not indicated */
724 put_bits(&s->pb, 1, s->lfe); /* LFE */
725 put_bits(&s->pb, 5, 31); /* dialog norm: -31 db */
726 put_bits(&s->pb, 1, 0); /* no compression control word */
727 put_bits(&s->pb, 1, 0); /* no lang code */
728 put_bits(&s->pb, 1, 0); /* no audio production info */
729 put_bits(&s->pb, 1, 0); /* no copyright */
730 put_bits(&s->pb, 1, 1); /* original bitstream */
731 put_bits(&s->pb, 1, 0); /* no time code 1 */
732 put_bits(&s->pb, 1, 0); /* no time code 2 */
733 put_bits(&s->pb, 1, 0); /* no additional bit stream info */
736 /* symetric quantization on 'levels' levels */
737 static inline int sym_quant(int c, int e, int levels)
742 v = (levels * (c << e)) >> 24;
744 v = (levels >> 1) + v;
746 v = (levels * ((-c) << e)) >> 24;
748 v = (levels >> 1) - v;
750 assert (v >= 0 && v < levels);
754 /* asymetric quantization on 2^qbits levels */
755 static inline int asym_quant(int c, int e, int qbits)
759 lshift = e + qbits - 24;
766 m = (1 << (qbits-1));
770 return v & ((1 << qbits)-1);
773 /* Output one audio block. There are NB_BLOCKS audio blocks in one AC-3
775 static void output_audio_block(AC3EncodeContext *s,
776 uint8_t exp_strategy[AC3_MAX_CHANNELS],
777 uint8_t encoded_exp[AC3_MAX_CHANNELS][N/2],
778 uint8_t bap[AC3_MAX_CHANNELS][N/2],
779 int32_t mdct_coefs[AC3_MAX_CHANNELS][N/2],
780 int8_t global_exp[AC3_MAX_CHANNELS],
783 int ch, nb_groups, group_size, i, baie, rbnd;
785 uint16_t qmant[AC3_MAX_CHANNELS][N/2];
787 int mant1_cnt, mant2_cnt, mant4_cnt;
788 uint16_t *qmant1_ptr, *qmant2_ptr, *qmant4_ptr;
789 int delta0, delta1, delta2;
791 for(ch=0;ch<s->nb_channels;ch++)
792 put_bits(&s->pb, 1, 0); /* 512 point MDCT */
793 for(ch=0;ch<s->nb_channels;ch++)
794 put_bits(&s->pb, 1, 1); /* no dither */
795 put_bits(&s->pb, 1, 0); /* no dynamic range */
796 if (block_num == 0) {
797 /* for block 0, even if no coupling, we must say it. This is a
799 put_bits(&s->pb, 1, 1); /* coupling strategy present */
800 put_bits(&s->pb, 1, 0); /* no coupling strategy */
802 put_bits(&s->pb, 1, 0); /* no new coupling strategy */
805 if (s->channel_mode == AC3_CHMODE_STEREO)
809 /* first block must define rematrixing (rematstr) */
810 put_bits(&s->pb, 1, 1);
812 /* dummy rematrixing rematflg(1:4)=0 */
813 for (rbnd=0;rbnd<4;rbnd++)
814 put_bits(&s->pb, 1, 0);
818 /* no matrixing (but should be used in the future) */
819 put_bits(&s->pb, 1, 0);
825 static int count = 0;
826 av_log(NULL, AV_LOG_DEBUG, "Block #%d (%d)\n", block_num, count++);
829 /* exponent strategy */
830 for(ch=0;ch<s->nb_channels;ch++) {
831 put_bits(&s->pb, 2, exp_strategy[ch]);
835 put_bits(&s->pb, 1, exp_strategy[s->lfe_channel]);
838 for(ch=0;ch<s->nb_channels;ch++) {
839 if (exp_strategy[ch] != EXP_REUSE)
840 put_bits(&s->pb, 6, s->chbwcod[ch]);
844 for (ch = 0; ch < s->nb_all_channels; ch++) {
845 switch(exp_strategy[ch]) {
859 nb_groups = (s->nb_coefs[ch] + (group_size * 3) - 4) / (3 * group_size);
864 put_bits(&s->pb, 4, exp1);
866 /* next ones are delta encoded */
867 for(i=0;i<nb_groups;i++) {
868 /* merge three delta in one code */
872 delta0 = exp1 - exp0 + 2;
877 delta1 = exp1 - exp0 + 2;
882 delta2 = exp1 - exp0 + 2;
884 put_bits(&s->pb, 7, ((delta0 * 5 + delta1) * 5) + delta2);
887 if (ch != s->lfe_channel)
888 put_bits(&s->pb, 2, 0); /* no gain range info */
891 /* bit allocation info */
892 baie = (block_num == 0);
893 put_bits(&s->pb, 1, baie);
895 put_bits(&s->pb, 2, s->slow_decay_code);
896 put_bits(&s->pb, 2, s->fast_decay_code);
897 put_bits(&s->pb, 2, s->slow_gain_code);
898 put_bits(&s->pb, 2, s->db_per_bit_code);
899 put_bits(&s->pb, 3, s->floor_code);
903 put_bits(&s->pb, 1, baie); /* always present with bai */
905 put_bits(&s->pb, 6, s->coarse_snr_offset);
906 for(ch=0;ch<s->nb_all_channels;ch++) {
907 put_bits(&s->pb, 4, s->fine_snr_offset[ch]);
908 put_bits(&s->pb, 3, s->fast_gain_code[ch]);
912 put_bits(&s->pb, 1, 0); /* no delta bit allocation */
913 put_bits(&s->pb, 1, 0); /* no data to skip */
915 /* mantissa encoding : we use two passes to handle the grouping. A
916 one pass method may be faster, but it would necessitate to
917 modify the output stream. */
919 /* first pass: quantize */
920 mant1_cnt = mant2_cnt = mant4_cnt = 0;
921 qmant1_ptr = qmant2_ptr = qmant4_ptr = NULL;
923 for (ch = 0; ch < s->nb_all_channels; ch++) {
926 for(i=0;i<s->nb_coefs[ch];i++) {
927 c = mdct_coefs[ch][i];
928 e = encoded_exp[ch][i] - global_exp[ch];
935 v = sym_quant(c, e, 3);
938 qmant1_ptr = &qmant[ch][i];
943 *qmant1_ptr += 3 * v;
955 v = sym_quant(c, e, 5);
958 qmant2_ptr = &qmant[ch][i];
963 *qmant2_ptr += 5 * v;
975 v = sym_quant(c, e, 7);
978 v = sym_quant(c, e, 11);
981 qmant4_ptr = &qmant[ch][i];
993 v = sym_quant(c, e, 15);
996 v = asym_quant(c, e, 14);
999 v = asym_quant(c, e, 16);
1002 v = asym_quant(c, e, b - 1);
1009 /* second pass : output the values */
1010 for (ch = 0; ch < s->nb_all_channels; ch++) {
1013 for(i=0;i<s->nb_coefs[ch];i++) {
1021 put_bits(&s->pb, 5, q);
1025 put_bits(&s->pb, 7, q);
1028 put_bits(&s->pb, 3, q);
1032 put_bits(&s->pb, 7, q);
1035 put_bits(&s->pb, 14, q);
1038 put_bits(&s->pb, 16, q);
1041 put_bits(&s->pb, b - 1, q);
1048 #define CRC16_POLY ((1 << 0) | (1 << 2) | (1 << 15) | (1 << 16))
1050 static unsigned int mul_poly(unsigned int a, unsigned int b, unsigned int poly)
1066 static unsigned int pow_poly(unsigned int a, unsigned int n, unsigned int poly)
1072 r = mul_poly(r, a, poly);
1073 a = mul_poly(a, a, poly);
1080 /* compute log2(max(abs(tab[]))) */
1081 static int log2_tab(int16_t *tab, int n)
1092 static void lshift_tab(int16_t *tab, int n, int lshift)
1100 } else if (lshift < 0) {
1108 /* fill the end of the frame and compute the two crcs */
1109 static int output_frame_end(AC3EncodeContext *s)
1111 int frame_size, frame_size_58, n, crc1, crc2, crc_inv;
1114 frame_size = s->frame_size; /* frame size in words */
1115 /* align to 8 bits */
1116 flush_put_bits(&s->pb);
1117 /* add zero bytes to reach the frame size */
1119 n = 2 * s->frame_size - (pbBufPtr(&s->pb) - frame) - 2;
1122 memset(pbBufPtr(&s->pb), 0, n);
1124 /* Now we must compute both crcs : this is not so easy for crc1
1125 because it is at the beginning of the data... */
1126 frame_size_58 = (frame_size >> 1) + (frame_size >> 3);
1127 crc1 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,
1128 frame + 4, 2 * frame_size_58 - 4));
1129 /* XXX: could precompute crc_inv */
1130 crc_inv = pow_poly((CRC16_POLY >> 1), (16 * frame_size_58) - 16, CRC16_POLY);
1131 crc1 = mul_poly(crc_inv, crc1, CRC16_POLY);
1132 AV_WB16(frame+2,crc1);
1134 crc2 = bswap_16(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0,
1135 frame + 2 * frame_size_58,
1136 (frame_size - frame_size_58) * 2 - 2));
1137 AV_WB16(frame+2*frame_size-2,crc2);
1139 // printf("n=%d frame_size=%d\n", n, frame_size);
1140 return frame_size * 2;
1143 static int AC3_encode_frame(AVCodecContext *avctx,
1144 unsigned char *frame, int buf_size, void *data)
1146 AC3EncodeContext *s = avctx->priv_data;
1147 int16_t *samples = data;
1149 int16_t input_samples[N];
1150 int32_t mdct_coef[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
1151 uint8_t exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
1152 uint8_t exp_strategy[NB_BLOCKS][AC3_MAX_CHANNELS];
1153 uint8_t encoded_exp[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
1154 uint8_t bap[NB_BLOCKS][AC3_MAX_CHANNELS][N/2];
1155 int8_t exp_samples[NB_BLOCKS][AC3_MAX_CHANNELS];
1159 for(ch=0;ch<s->nb_all_channels;ch++) {
1160 /* fixed mdct to the six sub blocks & exponent computation */
1161 for(i=0;i<NB_BLOCKS;i++) {
1165 /* compute input samples */
1166 memcpy(input_samples, s->last_samples[ch], N/2 * sizeof(int16_t));
1167 sinc = s->nb_all_channels;
1168 sptr = samples + (sinc * (N/2) * i) + ch;
1169 for(j=0;j<N/2;j++) {
1171 input_samples[j + N/2] = v;
1172 s->last_samples[ch][j] = v;
1176 /* apply the MDCT window */
1177 for(j=0;j<N/2;j++) {
1178 input_samples[j] = MUL16(input_samples[j],
1179 ff_ac3_window[j]) >> 15;
1180 input_samples[N-j-1] = MUL16(input_samples[N-j-1],
1181 ff_ac3_window[j]) >> 15;
1184 /* Normalize the samples to use the maximum available
1186 v = 14 - log2_tab(input_samples, N);
1189 exp_samples[i][ch] = v - 9;
1190 lshift_tab(input_samples, N, v);
1193 mdct512(mdct_coef[i][ch], input_samples);
1195 /* compute "exponents". We take into account the
1196 normalization there */
1197 for(j=0;j<N/2;j++) {
1199 v = abs(mdct_coef[i][ch][j]);
1203 e = 23 - av_log2(v) + exp_samples[i][ch];
1206 mdct_coef[i][ch][j] = 0;
1213 compute_exp_strategy(exp_strategy, exp, ch, ch == s->lfe_channel);
1215 /* compute the exponents as the decoder will see them. The
1216 EXP_REUSE case must be handled carefully : we select the
1217 min of the exponents */
1219 while (i < NB_BLOCKS) {
1221 while (j < NB_BLOCKS && exp_strategy[j][ch] == EXP_REUSE) {
1222 exponent_min(exp[i][ch], exp[j][ch], s->nb_coefs[ch]);
1225 frame_bits += encode_exp(encoded_exp[i][ch],
1226 exp[i][ch], s->nb_coefs[ch],
1227 exp_strategy[i][ch]);
1228 /* copy encoded exponents for reuse case */
1229 for(k=i+1;k<j;k++) {
1230 memcpy(encoded_exp[k][ch], encoded_exp[i][ch],
1231 s->nb_coefs[ch] * sizeof(uint8_t));
1237 /* adjust for fractional frame sizes */
1238 while(s->bits_written >= s->bit_rate && s->samples_written >= s->sample_rate) {
1239 s->bits_written -= s->bit_rate;
1240 s->samples_written -= s->sample_rate;
1242 s->frame_size = s->frame_size_min + (s->bits_written * s->sample_rate < s->samples_written * s->bit_rate);
1243 s->bits_written += s->frame_size * 16;
1244 s->samples_written += AC3_FRAME_SIZE;
1246 compute_bit_allocation(s, bap, encoded_exp, exp_strategy, frame_bits);
1247 /* everything is known... let's output the frame */
1248 output_frame_header(s, frame);
1250 for(i=0;i<NB_BLOCKS;i++) {
1251 output_audio_block(s, exp_strategy[i], encoded_exp[i],
1252 bap[i], mdct_coef[i], exp_samples[i], i);
1254 return output_frame_end(s);
1257 static av_cold int AC3_encode_close(AVCodecContext *avctx)
1259 av_freep(&avctx->coded_frame);
1264 /*************************************************************************/
1272 IComplex in[FN], in1[FN];
1274 float sum_re, sum_im, a;
1279 in[i].re = random() % 65535 - 32767;
1280 in[i].im = random() % 65535 - 32767;
1290 a = -2 * M_PI * (n * k) / FN;
1291 sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);
1292 sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);
1294 printf("%3d: %6d,%6d %6.0f,%6.0f\n",
1295 k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);
1299 void mdct_test(void)
1302 int32_t output[N/2];
1305 float s, a, err, e, emax;
1309 input[i] = (random() % 65535 - 32767) * 9 / 10;
1310 input1[i] = input[i];
1313 mdct512(output, input);
1316 for(k=0;k<N/2;k++) {
1319 a = (2*M_PI*(2*n+1+N/2)*(2*k+1) / (4 * N));
1320 s += input1[n] * cos(a);
1322 output1[k] = -2 * s / N;
1327 for(i=0;i<N/2;i++) {
1328 printf("%3d: %7d %7.0f\n", i, output[i], output1[i]);
1329 e = output[i] - output1[i];
1334 printf("err2=%f emax=%f\n", err / (N/2), emax);
1339 AC3EncodeContext ctx;
1340 unsigned char frame[AC3_MAX_CODED_FRAME_SIZE];
1341 short samples[AC3_FRAME_SIZE];
1344 AC3_encode_init(&ctx, 44100, 64000, 1);
1349 for(i=0;i<AC3_FRAME_SIZE;i++)
1350 samples[i] = (int)(sin(2*M_PI*i*1000.0/44100) * 10000);
1351 ret = AC3_encode_frame(&ctx, frame, samples);
1352 printf("ret=%d\n", ret);
1356 AVCodec ac3_encoder = {
1360 sizeof(AC3EncodeContext),
1365 .sample_fmts = (enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},
1366 .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),