Revision 5066f515 libavcodec/ac3dec.c

View differences:

libavcodec/ac3dec.c
44 44
 */
45 45
static const uint8_t rematrix_band_tbl[5] = { 13, 25, 37, 61, 253 };
46 46

  
47
/* table for exponent to scale_factor mapping
48
 * scale_factor[i] = 2 ^ -(i + 15)
47
/**
48
 * table for exponent to scale_factor mapping
49
 * scale_factors[i] = 2 ^ -i
49 50
 */
50 51
static float scale_factors[25];
51 52

  
......
75 76
/** dialogue normalization table */
76 77
static float dialnorm_tbl[32];
77 78

  
78
/* Adjustmens in dB gain */
79
/** Adjustments in dB gain */
79 80
#define LEVEL_MINUS_3DB         0.7071067811865476
80 81
#define LEVEL_MINUS_4POINT5DB   0.5946035575013605
81 82
#define LEVEL_MINUS_6DB         0.5000000000000000
......
127 128
#define AC3_OUTPUT_LFEON  8
128 129

  
129 130
typedef struct {
130
    int acmod;
131
    int dsurmod;
132
    int blksw[AC3_MAX_CHANNELS];
133
    int dithflag[AC3_MAX_CHANNELS];
134
    int dither_all;
135
    int cplinu;
136
    int chincpl[AC3_MAX_CHANNELS];
137
    int phsflginu;
138
    int cplbndstrc[18];
139
    int rematstr;
140
    int nrematbnd;
141
    int rematflg[4];
142
    int expstr[AC3_MAX_CHANNELS];
143
    int snroffst[AC3_MAX_CHANNELS];
144
    int fgain[AC3_MAX_CHANNELS];
145
    int deltbae[AC3_MAX_CHANNELS];
146
    int deltnseg[AC3_MAX_CHANNELS];
147
    uint8_t  deltoffst[AC3_MAX_CHANNELS][8];
148
    uint8_t  deltlen[AC3_MAX_CHANNELS][8];
149
    uint8_t  deltba[AC3_MAX_CHANNELS][8];
150

  
151
    /* Derived Attributes. */
152
    int      sampling_rate;
153
    int      bit_rate;
154
    int      frame_size;
155

  
156
    int      nchans;            //number of total channels
157
    int      nfchans;           //number of full-bandwidth channels
158
    int      lfeon;             //lfe channel in use
131
    int acmod;                              ///< audio coding mode
132
    int dsurmod;                            ///< dolby surround mode
133
    int blksw[AC3_MAX_CHANNELS];            ///< block switch flags
134
    int dithflag[AC3_MAX_CHANNELS];         ///< dither flags
135
    int dither_all;                         ///< true if all channels are dithered
136
    int cplinu;                             ///< coupling in use
137
    int chincpl[AC3_MAX_CHANNELS];          ///< channel in coupling
138
    int phsflginu;                          ///< phase flags in use
139
    int cplbndstrc[18];                     ///< coupling band structure
140
    int rematstr;                           ///< rematrixing strategy
141
    int nrematbnd;                          ///< number of rematrixing bands
142
    int rematflg[4];                        ///< rematrixing flags
143
    int expstr[AC3_MAX_CHANNELS];           ///< exponent strategies
144
    int snroffst[AC3_MAX_CHANNELS];         ///< signal-to-noise ratio offsets
145
    int fgain[AC3_MAX_CHANNELS];            ///< fast gain values (signal-to-mask ratio)
146
    int deltbae[AC3_MAX_CHANNELS];          ///< delta bit allocation exists
147
    int deltnseg[AC3_MAX_CHANNELS];         ///< number of delta segments
148
    uint8_t deltoffst[AC3_MAX_CHANNELS][8]; ///< delta segment offsets
149
    uint8_t deltlen[AC3_MAX_CHANNELS][8];   ///< delta segment lengths
150
    uint8_t deltba[AC3_MAX_CHANNELS][8];    ///< delta values for each segment
151

  
152
    int sampling_rate;                      ///< sample frequency, in Hz
153
    int bit_rate;                           ///< stream bit rate, in bits-per-second
154
    int frame_size;                         ///< current frame size, in bytes
155

  
156
    int nchans;                             ///< number of total channels
157
    int nfchans;                            ///< number of full-bandwidth channels
158
    int lfeon;                              ///< lfe channel in use
159 159
    int      lfe_ch;            ///< index of LFE channel
160 160
    int      output_mode;       ///< output channel configuration
161 161
    int      out_channels;      ///< number of output channels
......
163 163
    float    downmix_coeffs[AC3_MAX_CHANNELS][2];   ///< stereo downmix coefficients
164 164
    float    dialnorm[2];                       ///< dialogue normalization
165 165
    float    dynrng[2];                         ///< dynamic range
166
    float    cplco[AC3_MAX_CHANNELS][18];   //coupling coordinates
167
    int      ncplbnd;           //number of coupling bands
168
    int      ncplsubnd;         //number of coupling sub bands
166
    float cplco[AC3_MAX_CHANNELS][18];      ///< coupling coordinates
167
    int ncplbnd;                            ///< number of coupling bands
168
    int ncplsubnd;                          ///< number of coupling sub bands
169 169
    int      startmant[AC3_MAX_CHANNELS];   ///< start frequency bin
170
    int      endmant[AC3_MAX_CHANNELS];     //channel end mantissas
170
    int endmant[AC3_MAX_CHANNELS];          ///< end frequency bin
171 171
    AC3BitAllocParameters bit_alloc_params; ///< bit allocation parameters
172 172

  
173 173
    int8_t   dexps[AC3_MAX_CHANNELS][256];  ///< decoded exponents
......
176 176
    int16_t  bndpsd[AC3_MAX_CHANNELS][50];  ///< interpolated exponents
177 177
    int16_t  mask[AC3_MAX_CHANNELS][50];    ///< masking curve values
178 178

  
179
    DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][256]);  //transform coefficients
179
    DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][256]);  ///< transform coefficients
180 180

  
181 181
    /* For IMDCT. */
182
    MDCTContext imdct_512;  //for 512 sample imdct transform
183
    MDCTContext imdct_256;  //for 256 sample imdct transform
184
    DSPContext  dsp;        //for optimization
182
    MDCTContext imdct_512;                  ///< for 512 sample IMDCT
183
    MDCTContext imdct_256;                  ///< for 256 sample IMDCT
184
    DSPContext  dsp;                        ///< for optimization
185 185
    float       add_bias;   ///< offset for float_to_int16 conversion
186 186
    float       mul_bias;   ///< scaling for float_to_int16 conversion
187 187

  
188
    DECLARE_ALIGNED_16(float, output[AC3_MAX_CHANNELS-1][256]); //output after imdct transform and windowing
188
    DECLARE_ALIGNED_16(float, output[AC3_MAX_CHANNELS-1][256]);     ///< output after imdct transform and windowing
189 189
    DECLARE_ALIGNED_16(short, int_output[AC3_MAX_CHANNELS-1][256]); ///< final 16-bit integer output
190
    DECLARE_ALIGNED_16(float, delay[AC3_MAX_CHANNELS-1][256]);  //delay - added to the next block
191
    DECLARE_ALIGNED_16(float, tmp_imdct[256]);                  //temporary storage for imdct transform
192
    DECLARE_ALIGNED_16(float, tmp_output[512]);                 //temporary storage for output before windowing
193
    DECLARE_ALIGNED_16(float, window[256]);                     //window coefficients
190
    DECLARE_ALIGNED_16(float, delay[AC3_MAX_CHANNELS-1][256]);      ///< delay - added to the next block
191
    DECLARE_ALIGNED_16(float, tmp_imdct[256]);                      ///< temporary storage for imdct transform
192
    DECLARE_ALIGNED_16(float, tmp_output[512]);                     ///< temporary storage for output before windowing
193
    DECLARE_ALIGNED_16(float, window[256]);                         ///< window coefficients
194 194

  
195 195
    /* Miscellaneous. */
196
    GetBitContext gb;
197
    AVRandomState dith_state;   //for dither generation
196
    GetBitContext gb;                       ///< bitstream reader
197
    AVRandomState dith_state;               ///< for dither generation
198 198
    AVCodecContext *avctx;      ///< parent context
199 199
} AC3DecodeContext;
200 200

  
......
211 211
   for (i = 0; i < 256; i++) {
212 212
       tmp = i * (256 - i) * alpha2;
213 213
       bessel = 1.0;
214
       for (j = 100; j > 0; j--) /* defaul to 100 iterations */
214
       for (j = 100; j > 0; j--) /* default to 100 iterations */
215 215
           bessel = bessel * tmp / (j * j) + 1;
216 216
       sum += bessel;
217 217
       local_window[i] = sum;
......
222 222
       window[i] = sqrt(local_window[i] / sum);
223 223
}
224 224

  
225
/**
226
 * Symmetrical Dequantization
227
 * reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization
228
 *            Tables 7.19 to 7.23
229
 */
225 230
static inline float
226 231
symmetric_dequant(int code, int levels)
227 232
{
......
279 284
    }
280 285
    dialnorm_tbl[0] = dialnorm_tbl[31];
281 286

  
282
    //generate scale factors
287
    /* generate scale factors for exponents and asymmetrical dequantization
288
       reference: Section 7.3.2 Expansion of Mantissas for Asymmetric Quantization */
283 289
    for (i = 0; i < 25; i++)
284 290
        scale_factors[i] = pow(2.0, -i);
285 291

  
......
293 299
}
294 300

  
295 301

  
302
/**
303
 * AVCodec initialization
304
 */
296 305
static int ac3_decode_init(AVCodecContext *avctx)
297 306
{
298 307
    AC3DecodeContext *ctx = avctx->priv_data;
......
306 315
    dsputil_init(&ctx->dsp, avctx);
307 316
    av_init_random(0, &ctx->dith_state);
308 317

  
318
    /* set bias values for float to int16 conversion */
309 319
    if(ctx->dsp.float_to_int16 == ff_float_to_int16_c) {
310 320
        ctx->add_bias = 385.0f;
311 321
        ctx->mul_bias = 1.0f;
......
318 328
}
319 329

  
320 330
/**
321
 * Parses the 'sync info' and 'bit stream info' from the AC-3 bitstream.
331
 * Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.
322 332
 * GetBitContext within AC3DecodeContext must point to
323 333
 * start of the synchronized ac3 bitstream.
324 334
 */
......
355 365
        ctx->output_mode |= AC3_OUTPUT_LFEON;
356 366

  
357 367
    /* skip over portion of header which has already been read */
358
    skip_bits(gb, 16); //skip the sync_word, sync_info->sync_word = get_bits(gb, 16);
368
    skip_bits(gb, 16); // skip the sync_word
359 369
    skip_bits(gb, 16); // skip crc1
360 370
    skip_bits(gb, 8);  // skip fscod and frmsizecod
361 371
    skip_bits(gb, 11); // skip bsid, bsmod, and acmod
......
383 393

  
384 394
    skip_bits(gb, 2); //skip copyright bit and original bitstream bit
385 395

  
386
    /* FIXME: read & use the xbsi1 downmix levels */
396
    /* skip the timecodes (or extra bitstream information for Alternate Syntax)
397
       TODO: read & use the xbsi1 downmix levels */
387 398
    if (get_bits1(gb))
388
        skip_bits(gb, 14); //skip timecode1
399
        skip_bits(gb, 14); //skip timecode1 / xbsi1
389 400
    if (get_bits1(gb))
390
        skip_bits(gb, 14); //skip timecode2
401
        skip_bits(gb, 14); //skip timecode2 / xbsi2
391 402

  
403
    /* skip additional bitstream info */
392 404
    if (get_bits1(gb)) {
393
        i = get_bits(gb, 6); //additional bsi length
405
        i = get_bits(gb, 6);
394 406
        do {
395 407
            skip_bits(gb, 8);
396 408
        } while(i--);
......
418 430
}
419 431

  
420 432
/**
421
 * Decodes the grouped exponents.
422
 * This function decodes the coded exponents according to exponent strategy
423
 * and stores them in the decoded exponents buffer.
424
 *
425
 * @param[in]  gb      GetBitContext which points to start of coded exponents
426
 * @param[in]  expstr  Exponent coding strategy
427
 * @param[in]  ngrps   Number of grouped exponents
428
 * @param[in]  absexp  Absolute exponent or DC exponent
429
 * @param[out] dexps   Decoded exponents are stored in dexps
433
 * Decode the grouped exponents according to exponent strategy.
434
 * reference: Section 7.1.3 Exponent Decoding
430 435
 */
431 436
static void decode_exponents(GetBitContext *gb, int expstr, int ngrps,
432 437
                             uint8_t absexp, int8_t *dexps)
......
455 460
}
456 461

  
457 462
/**
458
 * Generates transform coefficients for each coupled channel in the coupling
463
 * Generate transform coefficients for each coupled channel in the coupling
459 464
 * range using the coupling coefficients and coupling coordinates.
460 465
 * reference: Section 7.4.3 Coupling Coordinate Format
461 466
 */
......
479 484
    }
480 485
}
481 486

  
482
typedef struct { /* grouped mantissas for 3-level 5-leve and 11-level quantization */
487
/**
488
 * Grouped mantissas for 3-level 5-level and 11-level quantization
489
 */
490
typedef struct {
483 491
    float b1_mant[3];
484 492
    float b2_mant[3];
485 493
    float b4_mant[2];
......
488 496
    int b4ptr;
489 497
} mant_groups;
490 498

  
491
/* Get the transform coefficients for particular channel */
499
/**
500
 * Get the transform coefficients for a particular channel
501
 * reference: Section 7.3 Quantization and Decoding of Mantissas
502
 */
492 503
static int get_transform_coeffs_ch(AC3DecodeContext *ctx, int ch_index, mant_groups *m)
493 504
{
494 505
    GetBitContext *gb = &ctx->gb;
......
551 562
                break;
552 563

  
553 564
            default:
565
                /* asymmetric dequantization */
554 566
                coeffs[i] = get_sbits(gb, qntztab[tbap]) * scale_factors[qntztab[tbap]-1];
555 567
                break;
556 568
        }
......
561 573
}
562 574

  
563 575
/**
564
 * Removes random dithering from coefficients with zero-bit mantissas
576
 * Remove random dithering from coefficients with zero-bit mantissas
565 577
 * reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)
566 578
 */
567 579
static void remove_dithering(AC3DecodeContext *ctx) {
......
593 605
    }
594 606
}
595 607

  
596
/* Get the transform coefficients.
597
 * This function extracts the tranform coefficients form the ac3 bitstream.
598
 * This function is called after bit allocation is performed.
608
/**
609
 * Get the transform coefficients.
599 610
 */
600 611
static int get_transform_coeffs(AC3DecodeContext * ctx)
601 612
{
......
606 617
    m.b1ptr = m.b2ptr = m.b4ptr = 3;
607 618

  
608 619
    for (ch = 1; ch <= ctx->nchans; ch++) {
609
        /* transform coefficients for individual channel */
620
        /* transform coefficients for full-bandwidth channel */
610 621
        if (get_transform_coeffs_ch(ctx, ch, &m))
611 622
            return -1;
612
        /* tranform coefficients for coupling channels */
623
        /* tranform coefficients for coupling channel come right after the
624
           coefficients for the first coupled channel*/
613 625
        if (ctx->chincpl[ch])  {
614 626
            if (!got_cplchan) {
615 627
                if (get_transform_coeffs_ch(ctx, CPL_CH, &m)) {
......
636 648
}
637 649

  
638 650
/**
639
 * Performs stereo rematrixing.
651
 * Stereo rematrixing.
640 652
 * reference: Section 7.5.4 Rematrixing : Decoding Technique
641 653
 */
642 654
static void do_rematrixing(AC3DecodeContext *ctx)
......
660 672
    }
661 673
}
662 674

  
663
/* This function performs the imdct on 256 sample transform
664
 * coefficients.
675
/**
676
 * Perform the 256-point IMDCT
665 677
 */
666 678
static void do_imdct_256(AC3DecodeContext *ctx, int chindex)
667 679
{
......
701 713
    }
702 714
}
703 715

  
704
/* IMDCT Transform. */
716
/**
717
 * Inverse MDCT Transform.
718
 * Convert frequency domain coefficients to time-domain audio samples.
719
 * reference: Section 7.9.4 Transformation Equations
720
 */
705 721
static inline void do_imdct(AC3DecodeContext *ctx)
706 722
{
707 723
    int ch;
708 724
    int nchans;
709 725

  
726
    /* Don't perform the IMDCT on the LFE channel unless it's used in the output */
710 727
    nchans = ctx->nfchans;
711 728
    if(ctx->output_mode & AC3_OUTPUT_LFEON)
712 729
        nchans++;
......
719 736
                                          ctx->transform_coeffs[ch],
720 737
                                          ctx->tmp_imdct);
721 738
        }
739
        /* For the first half of the block, apply the window, add the delay
740
           from the previous block, and send to output */
722 741
        ctx->dsp.vector_fmul_add_add(ctx->output[ch-1], ctx->tmp_output,
723 742
                                     ctx->window, ctx->delay[ch-1], 0, 256, 1);
743
        /* For the second half of the block, apply the window and store the
744
           samples to delay, to be combined with the next block */
724 745
        ctx->dsp.vector_fmul_reverse(ctx->delay[ch-1], ctx->tmp_output+256,
725 746
                                     ctx->window, 256);
726 747
    }
727 748
}
728 749

  
729 750
/**
730
 * Downmixes the output to stereo.
751
 * Downmix the output to mono or stereo.
731 752
 */
732 753
static void ac3_downmix(float samples[AC3_MAX_CHANNELS][256], int nfchans,
733 754
                        int output_mode, float coef[AC3_MAX_CHANNELS][2])
......
754 775
    }
755 776
}
756 777

  
757
/* Parse the audio block from ac3 bitstream.
758
 * This function extract the audio block from the ac3 bitstream
759
 * and produces the output for the block. This function must
760
 * be called for each of the six audio block in the ac3 bitstream.
778
/**
779
 * Parse an audio block from AC-3 bitstream.
761 780
 */
762 781
static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
763 782
{
......
769 788

  
770 789
    memset(bit_alloc_stages, 0, AC3_MAX_CHANNELS);
771 790

  
772
    for (ch = 1; ch <= nfchans; ch++) /*block switch flag */
791
    /* block switch flags */
792
    for (ch = 1; ch <= nfchans; ch++)
773 793
        ctx->blksw[ch] = get_bits1(gb);
774 794

  
795
    /* dithering flags */
775 796
    ctx->dither_all = 1;
776
    for (ch = 1; ch <= nfchans; ch++) { /* dithering flag */
797
    for (ch = 1; ch <= nfchans; ch++) {
777 798
        ctx->dithflag[ch] = get_bits1(gb);
778 799
        if(!ctx->dithflag[ch])
779 800
            ctx->dither_all = 0;
......
789 810
        }
790 811
    } while(i--);
791 812

  
792
    if (get_bits1(gb)) { /* coupling strategy */
813
    /* coupling strategy */
814
    if (get_bits1(gb)) {
793 815
        memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
794 816
        ctx->cplinu = get_bits1(gb);
795
        if (ctx->cplinu) { /* coupling in use */
817
        if (ctx->cplinu) {
818
            /* coupling in use */
796 819
            int cplbegf, cplendf;
797 820

  
821
            /* determine which channels are coupled */
798 822
            for (ch = 1; ch <= nfchans; ch++)
799 823
                ctx->chincpl[ch] = get_bits1(gb);
800 824

  
825
            /* phase flags in use */
801 826
            if (acmod == AC3_ACMOD_STEREO)
802
                ctx->phsflginu = get_bits1(gb); //phase flag in use
827
                ctx->phsflginu = get_bits1(gb);
803 828

  
829
            /* coupling frequency range and band structure */
804 830
            cplbegf = get_bits(gb, 4);
805 831
            cplendf = get_bits(gb, 4);
806

  
807 832
            if (3 + cplendf - cplbegf < 0) {
808 833
                av_log(ctx->avctx, AV_LOG_ERROR, "cplendf = %d < cplbegf = %d\n", cplendf, cplbegf);
809 834
                return -1;
810 835
            }
811

  
812 836
            ctx->ncplbnd = ctx->ncplsubnd = 3 + cplendf - cplbegf;
813 837
            ctx->startmant[CPL_CH] = cplbegf * 12 + 37;
814 838
            ctx->endmant[CPL_CH] = cplendf * 12 + 73;
815
            for (bnd = 0; bnd < ctx->ncplsubnd - 1; bnd++) { /* coupling band structure */
839
            for (bnd = 0; bnd < ctx->ncplsubnd - 1; bnd++) {
816 840
                if (get_bits1(gb)) {
817 841
                    ctx->cplbndstrc[bnd] = 1;
818 842
                    ctx->ncplbnd--;
819 843
                }
820 844
            }
821 845
        } else {
846
            /* coupling not in use */
822 847
            for (ch = 1; ch <= nfchans; ch++)
823 848
                ctx->chincpl[ch] = 0;
824 849
        }
825 850
    }
826 851

  
852
    /* coupling coordinates */
827 853
    if (ctx->cplinu) {
828 854
        int cplcoe = 0;
829 855

  
830 856
        for (ch = 1; ch <= nfchans; ch++) {
831 857
            if (ctx->chincpl[ch]) {
832
                if (get_bits1(gb)) { /* coupling co-ordinates */
858
                if (get_bits1(gb)) {
833 859
                    int mstrcplco, cplcoexp, cplcomant;
834 860
                    cplcoe = 1;
835 861
                    mstrcplco = 3 * get_bits(gb, 2);
......
845 871
                }
846 872
            }
847 873
        }
848

  
874
        /* phase flags */
849 875
        if (acmod == AC3_ACMOD_STEREO && ctx->phsflginu && cplcoe) {
850 876
            for (bnd = 0; bnd < ctx->ncplbnd; bnd++) {
851 877
                if (get_bits1(gb))
......
854 880
        }
855 881
    }
856 882

  
857
    if (acmod == AC3_ACMOD_STEREO) {/* rematrixing */
883
    /* stereo rematrixing strategy and band structure */
884
    if (acmod == AC3_ACMOD_STEREO) {
858 885
        ctx->rematstr = get_bits1(gb);
859 886
        if (ctx->rematstr) {
860 887
            ctx->nrematbnd = 4;
......
865 892
        }
866 893
    }
867 894

  
895
    /* exponent strategies for each channel */
868 896
    ctx->expstr[CPL_CH] = EXP_REUSE;
869 897
    ctx->expstr[ctx->lfe_ch] = EXP_REUSE;
870 898
    for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) {
......
876 904
            bit_alloc_stages[ch] = 3;
877 905
    }
878 906

  
879
    for (ch = 1; ch <= nfchans; ch++) { /* channel bandwidth code */
907
    /* channel bandwidth */
908
    for (ch = 1; ch <= nfchans; ch++) {
880 909
        ctx->startmant[ch] = 0;
881 910
        if (ctx->expstr[ch] != EXP_REUSE) {
882 911
            int prev = ctx->endmant[ch];
......
897 926
    ctx->startmant[ctx->lfe_ch] = 0;
898 927
    ctx->endmant[ctx->lfe_ch] = 7;
899 928

  
929
    /* decode exponents for each channel */
900 930
    for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) {
901 931
        if (ctx->expstr[ch] != EXP_REUSE) {
902 932
            int grpsize, ngrps;
......
915 945
        }
916 946
    }
917 947

  
918
    if (get_bits1(gb)) { /* bit allocation information */
948
    /* bit allocation information */
949
    if (get_bits1(gb)) {
919 950
        ctx->bit_alloc_params.sdecay = ff_sdecaytab[get_bits(gb, 2)];
920 951
        ctx->bit_alloc_params.fdecay = ff_fdecaytab[get_bits(gb, 2)];
921 952
        ctx->bit_alloc_params.sgain  = ff_sgaintab[get_bits(gb, 2)];
......
926 957
        }
927 958
    }
928 959

  
929
    if (get_bits1(gb)) { /* snroffset */
960
    /* signal-to-noise ratio offsets and fast gains (signal-to-mask ratios) */
961
    if (get_bits1(gb)) {
930 962
        int csnr;
931 963
        csnr = (get_bits(gb, 6) - 15) << 4;
932 964
        for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) { /* snr offset and fast gain */
......
936 968
        memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
937 969
    }
938 970

  
939
    if (ctx->cplinu && get_bits1(gb)) { /* coupling leak information */
971
    /* coupling leak information */
972
    if (ctx->cplinu && get_bits1(gb)) {
940 973
        ctx->bit_alloc_params.cplfleak = get_bits(gb, 3);
941 974
        ctx->bit_alloc_params.cplsleak = get_bits(gb, 3);
942 975
        bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);
943 976
    }
944 977

  
945
    if (get_bits1(gb)) { /* delta bit allocation information */
978
    /* delta bit allocation information */
979
    if (get_bits1(gb)) {
980
        /* delta bit allocation exists (strategy) */
946 981
        for (ch = !ctx->cplinu; ch <= nfchans; ch++) {
947 982
            ctx->deltbae[ch] = get_bits(gb, 2);
948 983
            if (ctx->deltbae[ch] == DBA_RESERVED) {
......
951 986
            }
952 987
            bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
953 988
        }
989
        /* channel delta offset, len and bit allocation */
954 990
        for (ch = !ctx->cplinu; ch <= nfchans; ch++) {
955
            if (ctx->deltbae[ch] == DBA_NEW) {/*channel delta offset, len and bit allocation */
991
            if (ctx->deltbae[ch] == DBA_NEW) {
956 992
                ctx->deltnseg[ch] = get_bits(gb, 3);
957 993
                for (seg = 0; seg <= ctx->deltnseg[ch]; seg++) {
958 994
                    ctx->deltoffst[ch][seg] = get_bits(gb, 5);
......
967 1003
        }
968 1004
    }
969 1005

  
1006
    /* Bit allocation */
970 1007
    for(ch=!ctx->cplinu; ch<=ctx->nchans; ch++) {
971 1008
        if(bit_alloc_stages[ch] > 2) {
972 1009
            /* Exponent mapping into PSD and PSD integration */
......
994 1031
        }
995 1032
    }
996 1033

  
997
    if (get_bits1(gb)) { /* unused dummy data */
1034
    /* unused dummy data */
1035
    if (get_bits1(gb)) {
998 1036
        int skipl = get_bits(gb, 9);
999 1037
        while(skipl--)
1000 1038
            skip_bits(gb, 8);
1001 1039
    }
1002 1040

  
1003 1041
    /* unpack the transform coefficients
1004
     * * this also uncouples channels if coupling is in use.
1005
     */
1042
       this also uncouples channels if coupling is in use. */
1006 1043
    if (get_transform_coeffs(ctx)) {
1007 1044
        av_log(ctx->avctx, AV_LOG_ERROR, "Error in routine get_transform_coeffs\n");
1008 1045
        return -1;
......
1045 1082
    return 0;
1046 1083
}
1047 1084

  
1048
/* Decode ac3 frame.
1049
 *
1050
 * @param avctx Pointer to AVCodecContext
1051
 * @param data Pointer to pcm smaples
1052
 * @param data_size Set to number of pcm samples produced by decoding
1053
 * @param buf Data to be decoded
1054
 * @param buf_size Size of the buffer
1085
/**
1086
 * Decode a single AC-3 frame.
1055 1087
 */
1056 1088
static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size, uint8_t *buf, int buf_size)
1057 1089
{
......
1059 1091
    int16_t *out_samples = (int16_t *)data;
1060 1092
    int i, blk, ch;
1061 1093

  
1062
    //Initialize the GetBitContext with the start of valid AC3 Frame.
1094
    /* initialize the GetBitContext with the start of valid AC-3 Frame */
1063 1095
    init_get_bits(&ctx->gb, buf, buf_size * 8);
1064 1096

  
1065
    //Parse the syncinfo.
1097
    /* parse the syncinfo */
1066 1098
    if (ac3_parse_header(ctx)) {
1067 1099
        av_log(avctx, AV_LOG_ERROR, "\n");
1068 1100
        *data_size = 0;
......
1092 1124
    }
1093 1125
    ctx->out_channels = avctx->channels;
1094 1126

  
1095
    //Parse the Audio Blocks.
1127
    /* parse the audio blocks */
1096 1128
    for (blk = 0; blk < NB_BLOCKS; blk++) {
1097 1129
        if (ac3_parse_audio_block(ctx, blk)) {
1098 1130
            av_log(avctx, AV_LOG_ERROR, "error parsing the audio block\n");
......
1107 1139
    return ctx->frame_size;
1108 1140
}
1109 1141

  
1110
/* Uninitialize ac3 decoder.
1142
/**
1143
 * Uninitialize the AC-3 decoder.
1111 1144
 */
1112 1145
static int ac3_decode_end(AVCodecContext *avctx)
1113 1146
{

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