[FFmpeg-cvslog] r10001 - trunk/libavcodec/ac3dec.c
jbr
subversion
Thu Aug 9 02:36:49 CEST 2007
Author: jbr
Date: Thu Aug 9 02:36:49 2007
New Revision: 10001
Log:
comments modification: add, clean up, deoxygenize, and reword
Modified:
trunk/libavcodec/ac3dec.c
Modified: trunk/libavcodec/ac3dec.c
==============================================================================
--- trunk/libavcodec/ac3dec.c (original)
+++ trunk/libavcodec/ac3dec.c Thu Aug 9 02:36:49 2007
@@ -44,8 +44,9 @@
*/
static const uint8_t rematrix_band_tbl[5] = { 13, 25, 37, 61, 253 };
-/* table for exponent to scale_factor mapping
- * scale_factor[i] = 2 ^ -(i + 15)
+/**
+ * table for exponent to scale_factor mapping
+ * scale_factors[i] = 2 ^ -i
*/
static float scale_factors[25];
@@ -75,7 +76,7 @@ static float dynrng_tbl[256];
/** dialogue normalization table */
static float dialnorm_tbl[32];
-/* Adjustmens in dB gain */
+/** Adjustments in dB gain */
#define LEVEL_MINUS_3DB 0.7071067811865476
#define LEVEL_MINUS_4POINT5DB 0.5946035575013605
#define LEVEL_MINUS_6DB 0.5000000000000000
@@ -127,35 +128,34 @@ static const uint8_t ac3_default_coeffs[
#define AC3_OUTPUT_LFEON 8
typedef struct {
- int acmod;
- int dsurmod;
- int blksw[AC3_MAX_CHANNELS];
- int dithflag[AC3_MAX_CHANNELS];
- int dither_all;
- int cplinu;
- int chincpl[AC3_MAX_CHANNELS];
- int phsflginu;
- int cplbndstrc[18];
- int rematstr;
- int nrematbnd;
- int rematflg[4];
- int expstr[AC3_MAX_CHANNELS];
- int snroffst[AC3_MAX_CHANNELS];
- int fgain[AC3_MAX_CHANNELS];
- int deltbae[AC3_MAX_CHANNELS];
- int deltnseg[AC3_MAX_CHANNELS];
- uint8_t deltoffst[AC3_MAX_CHANNELS][8];
- uint8_t deltlen[AC3_MAX_CHANNELS][8];
- uint8_t deltba[AC3_MAX_CHANNELS][8];
+ int acmod; ///< audio coding mode
+ int dsurmod; ///< dolby surround mode
+ int blksw[AC3_MAX_CHANNELS]; ///< block switch flags
+ int dithflag[AC3_MAX_CHANNELS]; ///< dither flags
+ int dither_all; ///< true if all channels are dithered
+ int cplinu; ///< coupling in use
+ int chincpl[AC3_MAX_CHANNELS]; ///< channel in coupling
+ int phsflginu; ///< phase flags in use
+ int cplbndstrc[18]; ///< coupling band structure
+ int rematstr; ///< rematrixing strategy
+ int nrematbnd; ///< number of rematrixing bands
+ int rematflg[4]; ///< rematrixing flags
+ int expstr[AC3_MAX_CHANNELS]; ///< exponent strategies
+ int snroffst[AC3_MAX_CHANNELS]; ///< signal-to-noise ratio offsets
+ int fgain[AC3_MAX_CHANNELS]; ///< fast gain values (signal-to-mask ratio)
+ int deltbae[AC3_MAX_CHANNELS]; ///< delta bit allocation exists
+ int deltnseg[AC3_MAX_CHANNELS]; ///< number of delta segments
+ uint8_t deltoffst[AC3_MAX_CHANNELS][8]; ///< delta segment offsets
+ uint8_t deltlen[AC3_MAX_CHANNELS][8]; ///< delta segment lengths
+ uint8_t deltba[AC3_MAX_CHANNELS][8]; ///< delta values for each segment
- /* Derived Attributes. */
- int sampling_rate;
- int bit_rate;
- int frame_size;
+ int sampling_rate; ///< sample frequency, in Hz
+ int bit_rate; ///< stream bit rate, in bits-per-second
+ int frame_size; ///< current frame size, in bytes
- int nchans; //number of total channels
- int nfchans; //number of full-bandwidth channels
- int lfeon; //lfe channel in use
+ int nchans; ///< number of total channels
+ int nfchans; ///< number of full-bandwidth channels
+ int lfeon; ///< lfe channel in use
int lfe_ch; ///< index of LFE channel
int output_mode; ///< output channel configuration
int out_channels; ///< number of output channels
@@ -163,11 +163,11 @@ typedef struct {
float downmix_coeffs[AC3_MAX_CHANNELS][2]; ///< stereo downmix coefficients
float dialnorm[2]; ///< dialogue normalization
float dynrng[2]; ///< dynamic range
- float cplco[AC3_MAX_CHANNELS][18]; //coupling coordinates
- int ncplbnd; //number of coupling bands
- int ncplsubnd; //number of coupling sub bands
+ float cplco[AC3_MAX_CHANNELS][18]; ///< coupling coordinates
+ int ncplbnd; ///< number of coupling bands
+ int ncplsubnd; ///< number of coupling sub bands
int startmant[AC3_MAX_CHANNELS]; ///< start frequency bin
- int endmant[AC3_MAX_CHANNELS]; //channel end mantissas
+ int endmant[AC3_MAX_CHANNELS]; ///< end frequency bin
AC3BitAllocParameters bit_alloc_params; ///< bit allocation parameters
int8_t dexps[AC3_MAX_CHANNELS][256]; ///< decoded exponents
@@ -176,25 +176,25 @@ typedef struct {
int16_t bndpsd[AC3_MAX_CHANNELS][50]; ///< interpolated exponents
int16_t mask[AC3_MAX_CHANNELS][50]; ///< masking curve values
- DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][256]); //transform coefficients
+ DECLARE_ALIGNED_16(float, transform_coeffs[AC3_MAX_CHANNELS][256]); ///< transform coefficients
/* For IMDCT. */
- MDCTContext imdct_512; //for 512 sample imdct transform
- MDCTContext imdct_256; //for 256 sample imdct transform
- DSPContext dsp; //for optimization
+ MDCTContext imdct_512; ///< for 512 sample IMDCT
+ MDCTContext imdct_256; ///< for 256 sample IMDCT
+ DSPContext dsp; ///< for optimization
float add_bias; ///< offset for float_to_int16 conversion
float mul_bias; ///< scaling for float_to_int16 conversion
- DECLARE_ALIGNED_16(float, output[AC3_MAX_CHANNELS-1][256]); //output after imdct transform and windowing
+ DECLARE_ALIGNED_16(float, output[AC3_MAX_CHANNELS-1][256]); ///< output after imdct transform and windowing
DECLARE_ALIGNED_16(short, int_output[AC3_MAX_CHANNELS-1][256]); ///< final 16-bit integer output
- DECLARE_ALIGNED_16(float, delay[AC3_MAX_CHANNELS-1][256]); //delay - added to the next block
- DECLARE_ALIGNED_16(float, tmp_imdct[256]); //temporary storage for imdct transform
- DECLARE_ALIGNED_16(float, tmp_output[512]); //temporary storage for output before windowing
- DECLARE_ALIGNED_16(float, window[256]); //window coefficients
+ DECLARE_ALIGNED_16(float, delay[AC3_MAX_CHANNELS-1][256]); ///< delay - added to the next block
+ DECLARE_ALIGNED_16(float, tmp_imdct[256]); ///< temporary storage for imdct transform
+ DECLARE_ALIGNED_16(float, tmp_output[512]); ///< temporary storage for output before windowing
+ DECLARE_ALIGNED_16(float, window[256]); ///< window coefficients
/* Miscellaneous. */
- GetBitContext gb;
- AVRandomState dith_state; //for dither generation
+ GetBitContext gb; ///< bitstream reader
+ AVRandomState dith_state; ///< for dither generation
AVCodecContext *avctx; ///< parent context
} AC3DecodeContext;
@@ -211,7 +211,7 @@ static void ac3_window_init(float *windo
for (i = 0; i < 256; i++) {
tmp = i * (256 - i) * alpha2;
bessel = 1.0;
- for (j = 100; j > 0; j--) /* defaul to 100 iterations */
+ for (j = 100; j > 0; j--) /* default to 100 iterations */
bessel = bessel * tmp / (j * j) + 1;
sum += bessel;
local_window[i] = sum;
@@ -222,6 +222,11 @@ static void ac3_window_init(float *windo
window[i] = sqrt(local_window[i] / sum);
}
+/**
+ * Symmetrical Dequantization
+ * reference: Section 7.3.3 Expansion of Mantissas for Symmetrical Quantization
+ * Tables 7.19 to 7.23
+ */
static inline float
symmetric_dequant(int code, int levels)
{
@@ -279,7 +284,8 @@ static void ac3_tables_init(void)
}
dialnorm_tbl[0] = dialnorm_tbl[31];
- //generate scale factors
+ /* generate scale factors for exponents and asymmetrical dequantization
+ reference: Section 7.3.2 Expansion of Mantissas for Asymmetric Quantization */
for (i = 0; i < 25; i++)
scale_factors[i] = pow(2.0, -i);
@@ -293,6 +299,9 @@ static void ac3_tables_init(void)
}
+/**
+ * AVCodec initialization
+ */
static int ac3_decode_init(AVCodecContext *avctx)
{
AC3DecodeContext *ctx = avctx->priv_data;
@@ -306,6 +315,7 @@ static int ac3_decode_init(AVCodecContex
dsputil_init(&ctx->dsp, avctx);
av_init_random(0, &ctx->dith_state);
+ /* set bias values for float to int16 conversion */
if(ctx->dsp.float_to_int16 == ff_float_to_int16_c) {
ctx->add_bias = 385.0f;
ctx->mul_bias = 1.0f;
@@ -318,7 +328,7 @@ static int ac3_decode_init(AVCodecContex
}
/**
- * Parses the 'sync info' and 'bit stream info' from the AC-3 bitstream.
+ * Parse the 'sync info' and 'bit stream info' from the AC-3 bitstream.
* GetBitContext within AC3DecodeContext must point to
* start of the synchronized ac3 bitstream.
*/
@@ -355,7 +365,7 @@ static int ac3_parse_header(AC3DecodeCon
ctx->output_mode |= AC3_OUTPUT_LFEON;
/* skip over portion of header which has already been read */
- skip_bits(gb, 16); //skip the sync_word, sync_info->sync_word = get_bits(gb, 16);
+ skip_bits(gb, 16); // skip the sync_word
skip_bits(gb, 16); // skip crc1
skip_bits(gb, 8); // skip fscod and frmsizecod
skip_bits(gb, 11); // skip bsid, bsmod, and acmod
@@ -383,14 +393,16 @@ static int ac3_parse_header(AC3DecodeCon
skip_bits(gb, 2); //skip copyright bit and original bitstream bit
- /* FIXME: read & use the xbsi1 downmix levels */
+ /* skip the timecodes (or extra bitstream information for Alternate Syntax)
+ TODO: read & use the xbsi1 downmix levels */
if (get_bits1(gb))
- skip_bits(gb, 14); //skip timecode1
+ skip_bits(gb, 14); //skip timecode1 / xbsi1
if (get_bits1(gb))
- skip_bits(gb, 14); //skip timecode2
+ skip_bits(gb, 14); //skip timecode2 / xbsi2
+ /* skip additional bitstream info */
if (get_bits1(gb)) {
- i = get_bits(gb, 6); //additional bsi length
+ i = get_bits(gb, 6);
do {
skip_bits(gb, 8);
} while(i--);
@@ -418,15 +430,8 @@ static int ac3_parse_header(AC3DecodeCon
}
/**
- * Decodes the grouped exponents.
- * This function decodes the coded exponents according to exponent strategy
- * and stores them in the decoded exponents buffer.
- *
- * @param[in] gb GetBitContext which points to start of coded exponents
- * @param[in] expstr Exponent coding strategy
- * @param[in] ngrps Number of grouped exponents
- * @param[in] absexp Absolute exponent or DC exponent
- * @param[out] dexps Decoded exponents are stored in dexps
+ * Decode the grouped exponents according to exponent strategy.
+ * reference: Section 7.1.3 Exponent Decoding
*/
static void decode_exponents(GetBitContext *gb, int expstr, int ngrps,
uint8_t absexp, int8_t *dexps)
@@ -455,7 +460,7 @@ static void decode_exponents(GetBitConte
}
/**
- * Generates transform coefficients for each coupled channel in the coupling
+ * Generate transform coefficients for each coupled channel in the coupling
* range using the coupling coefficients and coupling coordinates.
* reference: Section 7.4.3 Coupling Coordinate Format
*/
@@ -479,7 +484,10 @@ static void uncouple_channels(AC3DecodeC
}
}
-typedef struct { /* grouped mantissas for 3-level 5-leve and 11-level quantization */
+/**
+ * Grouped mantissas for 3-level 5-level and 11-level quantization
+ */
+typedef struct {
float b1_mant[3];
float b2_mant[3];
float b4_mant[2];
@@ -488,7 +496,10 @@ typedef struct { /* grouped mantissas fo
int b4ptr;
} mant_groups;
-/* Get the transform coefficients for particular channel */
+/**
+ * Get the transform coefficients for a particular channel
+ * reference: Section 7.3 Quantization and Decoding of Mantissas
+ */
static int get_transform_coeffs_ch(AC3DecodeContext *ctx, int ch_index, mant_groups *m)
{
GetBitContext *gb = &ctx->gb;
@@ -551,6 +562,7 @@ static int get_transform_coeffs_ch(AC3De
break;
default:
+ /* asymmetric dequantization */
coeffs[i] = get_sbits(gb, qntztab[tbap]) * scale_factors[qntztab[tbap]-1];
break;
}
@@ -561,7 +573,7 @@ static int get_transform_coeffs_ch(AC3De
}
/**
- * Removes random dithering from coefficients with zero-bit mantissas
+ * Remove random dithering from coefficients with zero-bit mantissas
* reference: Section 7.3.4 Dither for Zero Bit Mantissas (bap=0)
*/
static void remove_dithering(AC3DecodeContext *ctx) {
@@ -593,9 +605,8 @@ static void remove_dithering(AC3DecodeCo
}
}
-/* Get the transform coefficients.
- * This function extracts the tranform coefficients form the ac3 bitstream.
- * This function is called after bit allocation is performed.
+/**
+ * Get the transform coefficients.
*/
static int get_transform_coeffs(AC3DecodeContext * ctx)
{
@@ -606,10 +617,11 @@ static int get_transform_coeffs(AC3Decod
m.b1ptr = m.b2ptr = m.b4ptr = 3;
for (ch = 1; ch <= ctx->nchans; ch++) {
- /* transform coefficients for individual channel */
+ /* transform coefficients for full-bandwidth channel */
if (get_transform_coeffs_ch(ctx, ch, &m))
return -1;
- /* tranform coefficients for coupling channels */
+ /* tranform coefficients for coupling channel come right after the
+ coefficients for the first coupled channel*/
if (ctx->chincpl[ch]) {
if (!got_cplchan) {
if (get_transform_coeffs_ch(ctx, CPL_CH, &m)) {
@@ -636,7 +648,7 @@ static int get_transform_coeffs(AC3Decod
}
/**
- * Performs stereo rematrixing.
+ * Stereo rematrixing.
* reference: Section 7.5.4 Rematrixing : Decoding Technique
*/
static void do_rematrixing(AC3DecodeContext *ctx)
@@ -660,8 +672,8 @@ static void do_rematrixing(AC3DecodeCont
}
}
-/* This function performs the imdct on 256 sample transform
- * coefficients.
+/**
+ * Perform the 256-point IMDCT
*/
static void do_imdct_256(AC3DecodeContext *ctx, int chindex)
{
@@ -701,12 +713,17 @@ static void do_imdct_256(AC3DecodeContex
}
}
-/* IMDCT Transform. */
+/**
+ * Inverse MDCT Transform.
+ * Convert frequency domain coefficients to time-domain audio samples.
+ * reference: Section 7.9.4 Transformation Equations
+ */
static inline void do_imdct(AC3DecodeContext *ctx)
{
int ch;
int nchans;
+ /* Don't perform the IMDCT on the LFE channel unless it's used in the output */
nchans = ctx->nfchans;
if(ctx->output_mode & AC3_OUTPUT_LFEON)
nchans++;
@@ -719,15 +736,19 @@ static inline void do_imdct(AC3DecodeCon
ctx->transform_coeffs[ch],
ctx->tmp_imdct);
}
+ /* For the first half of the block, apply the window, add the delay
+ from the previous block, and send to output */
ctx->dsp.vector_fmul_add_add(ctx->output[ch-1], ctx->tmp_output,
ctx->window, ctx->delay[ch-1], 0, 256, 1);
+ /* For the second half of the block, apply the window and store the
+ samples to delay, to be combined with the next block */
ctx->dsp.vector_fmul_reverse(ctx->delay[ch-1], ctx->tmp_output+256,
ctx->window, 256);
}
}
/**
- * Downmixes the output to stereo.
+ * Downmix the output to mono or stereo.
*/
static void ac3_downmix(float samples[AC3_MAX_CHANNELS][256], int nfchans,
int output_mode, float coef[AC3_MAX_CHANNELS][2])
@@ -754,10 +775,8 @@ static void ac3_downmix(float samples[AC
}
}
-/* Parse the audio block from ac3 bitstream.
- * This function extract the audio block from the ac3 bitstream
- * and produces the output for the block. This function must
- * be called for each of the six audio block in the ac3 bitstream.
+/**
+ * Parse an audio block from AC-3 bitstream.
*/
static int ac3_parse_audio_block(AC3DecodeContext *ctx, int blk)
{
@@ -769,11 +788,13 @@ static int ac3_parse_audio_block(AC3Deco
memset(bit_alloc_stages, 0, AC3_MAX_CHANNELS);
- for (ch = 1; ch <= nfchans; ch++) /*block switch flag */
+ /* block switch flags */
+ for (ch = 1; ch <= nfchans; ch++)
ctx->blksw[ch] = get_bits1(gb);
+ /* dithering flags */
ctx->dither_all = 1;
- for (ch = 1; ch <= nfchans; ch++) { /* dithering flag */
+ for (ch = 1; ch <= nfchans; ch++) {
ctx->dithflag[ch] = get_bits1(gb);
if(!ctx->dithflag[ch])
ctx->dither_all = 0;
@@ -789,47 +810,52 @@ static int ac3_parse_audio_block(AC3Deco
}
} while(i--);
- if (get_bits1(gb)) { /* coupling strategy */
+ /* coupling strategy */
+ if (get_bits1(gb)) {
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
ctx->cplinu = get_bits1(gb);
- if (ctx->cplinu) { /* coupling in use */
+ if (ctx->cplinu) {
+ /* coupling in use */
int cplbegf, cplendf;
+ /* determine which channels are coupled */
for (ch = 1; ch <= nfchans; ch++)
ctx->chincpl[ch] = get_bits1(gb);
+ /* phase flags in use */
if (acmod == AC3_ACMOD_STEREO)
- ctx->phsflginu = get_bits1(gb); //phase flag in use
+ ctx->phsflginu = get_bits1(gb);
+ /* coupling frequency range and band structure */
cplbegf = get_bits(gb, 4);
cplendf = get_bits(gb, 4);
-
if (3 + cplendf - cplbegf < 0) {
av_log(ctx->avctx, AV_LOG_ERROR, "cplendf = %d < cplbegf = %d\n", cplendf, cplbegf);
return -1;
}
-
ctx->ncplbnd = ctx->ncplsubnd = 3 + cplendf - cplbegf;
ctx->startmant[CPL_CH] = cplbegf * 12 + 37;
ctx->endmant[CPL_CH] = cplendf * 12 + 73;
- for (bnd = 0; bnd < ctx->ncplsubnd - 1; bnd++) { /* coupling band structure */
+ for (bnd = 0; bnd < ctx->ncplsubnd - 1; bnd++) {
if (get_bits1(gb)) {
ctx->cplbndstrc[bnd] = 1;
ctx->ncplbnd--;
}
}
} else {
+ /* coupling not in use */
for (ch = 1; ch <= nfchans; ch++)
ctx->chincpl[ch] = 0;
}
}
+ /* coupling coordinates */
if (ctx->cplinu) {
int cplcoe = 0;
for (ch = 1; ch <= nfchans; ch++) {
if (ctx->chincpl[ch]) {
- if (get_bits1(gb)) { /* coupling co-ordinates */
+ if (get_bits1(gb)) {
int mstrcplco, cplcoexp, cplcomant;
cplcoe = 1;
mstrcplco = 3 * get_bits(gb, 2);
@@ -845,7 +871,7 @@ static int ac3_parse_audio_block(AC3Deco
}
}
}
-
+ /* phase flags */
if (acmod == AC3_ACMOD_STEREO && ctx->phsflginu && cplcoe) {
for (bnd = 0; bnd < ctx->ncplbnd; bnd++) {
if (get_bits1(gb))
@@ -854,7 +880,8 @@ static int ac3_parse_audio_block(AC3Deco
}
}
- if (acmod == AC3_ACMOD_STEREO) {/* rematrixing */
+ /* stereo rematrixing strategy and band structure */
+ if (acmod == AC3_ACMOD_STEREO) {
ctx->rematstr = get_bits1(gb);
if (ctx->rematstr) {
ctx->nrematbnd = 4;
@@ -865,6 +892,7 @@ static int ac3_parse_audio_block(AC3Deco
}
}
+ /* exponent strategies for each channel */
ctx->expstr[CPL_CH] = EXP_REUSE;
ctx->expstr[ctx->lfe_ch] = EXP_REUSE;
for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) {
@@ -876,7 +904,8 @@ static int ac3_parse_audio_block(AC3Deco
bit_alloc_stages[ch] = 3;
}
- for (ch = 1; ch <= nfchans; ch++) { /* channel bandwidth code */
+ /* channel bandwidth */
+ for (ch = 1; ch <= nfchans; ch++) {
ctx->startmant[ch] = 0;
if (ctx->expstr[ch] != EXP_REUSE) {
int prev = ctx->endmant[ch];
@@ -897,6 +926,7 @@ static int ac3_parse_audio_block(AC3Deco
ctx->startmant[ctx->lfe_ch] = 0;
ctx->endmant[ctx->lfe_ch] = 7;
+ /* decode exponents for each channel */
for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) {
if (ctx->expstr[ch] != EXP_REUSE) {
int grpsize, ngrps;
@@ -915,7 +945,8 @@ static int ac3_parse_audio_block(AC3Deco
}
}
- if (get_bits1(gb)) { /* bit allocation information */
+ /* bit allocation information */
+ if (get_bits1(gb)) {
ctx->bit_alloc_params.sdecay = ff_sdecaytab[get_bits(gb, 2)];
ctx->bit_alloc_params.fdecay = ff_fdecaytab[get_bits(gb, 2)];
ctx->bit_alloc_params.sgain = ff_sgaintab[get_bits(gb, 2)];
@@ -926,7 +957,8 @@ static int ac3_parse_audio_block(AC3Deco
}
}
- if (get_bits1(gb)) { /* snroffset */
+ /* signal-to-noise ratio offsets and fast gains (signal-to-mask ratios) */
+ if (get_bits1(gb)) {
int csnr;
csnr = (get_bits(gb, 6) - 15) << 4;
for (ch = !ctx->cplinu; ch <= ctx->nchans; ch++) { /* snr offset and fast gain */
@@ -936,13 +968,16 @@ static int ac3_parse_audio_block(AC3Deco
memset(bit_alloc_stages, 3, AC3_MAX_CHANNELS);
}
- if (ctx->cplinu && get_bits1(gb)) { /* coupling leak information */
+ /* coupling leak information */
+ if (ctx->cplinu && get_bits1(gb)) {
ctx->bit_alloc_params.cplfleak = get_bits(gb, 3);
ctx->bit_alloc_params.cplsleak = get_bits(gb, 3);
bit_alloc_stages[CPL_CH] = FFMAX(bit_alloc_stages[CPL_CH], 2);
}
- if (get_bits1(gb)) { /* delta bit allocation information */
+ /* delta bit allocation information */
+ if (get_bits1(gb)) {
+ /* delta bit allocation exists (strategy) */
for (ch = !ctx->cplinu; ch <= nfchans; ch++) {
ctx->deltbae[ch] = get_bits(gb, 2);
if (ctx->deltbae[ch] == DBA_RESERVED) {
@@ -951,8 +986,9 @@ static int ac3_parse_audio_block(AC3Deco
}
bit_alloc_stages[ch] = FFMAX(bit_alloc_stages[ch], 2);
}
+ /* channel delta offset, len and bit allocation */
for (ch = !ctx->cplinu; ch <= nfchans; ch++) {
- if (ctx->deltbae[ch] == DBA_NEW) {/*channel delta offset, len and bit allocation */
+ if (ctx->deltbae[ch] == DBA_NEW) {
ctx->deltnseg[ch] = get_bits(gb, 3);
for (seg = 0; seg <= ctx->deltnseg[ch]; seg++) {
ctx->deltoffst[ch][seg] = get_bits(gb, 5);
@@ -967,6 +1003,7 @@ static int ac3_parse_audio_block(AC3Deco
}
}
+ /* Bit allocation */
for(ch=!ctx->cplinu; ch<=ctx->nchans; ch++) {
if(bit_alloc_stages[ch] > 2) {
/* Exponent mapping into PSD and PSD integration */
@@ -994,15 +1031,15 @@ static int ac3_parse_audio_block(AC3Deco
}
}
- if (get_bits1(gb)) { /* unused dummy data */
+ /* unused dummy data */
+ if (get_bits1(gb)) {
int skipl = get_bits(gb, 9);
while(skipl--)
skip_bits(gb, 8);
}
/* unpack the transform coefficients
- * * this also uncouples channels if coupling is in use.
- */
+ this also uncouples channels if coupling is in use. */
if (get_transform_coeffs(ctx)) {
av_log(ctx->avctx, AV_LOG_ERROR, "Error in routine get_transform_coeffs\n");
return -1;
@@ -1045,13 +1082,8 @@ static int ac3_parse_audio_block(AC3Deco
return 0;
}
-/* Decode ac3 frame.
- *
- * @param avctx Pointer to AVCodecContext
- * @param data Pointer to pcm smaples
- * @param data_size Set to number of pcm samples produced by decoding
- * @param buf Data to be decoded
- * @param buf_size Size of the buffer
+/**
+ * Decode a single AC-3 frame.
*/
static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size, uint8_t *buf, int buf_size)
{
@@ -1059,10 +1091,10 @@ static int ac3_decode_frame(AVCodecConte
int16_t *out_samples = (int16_t *)data;
int i, blk, ch;
- //Initialize the GetBitContext with the start of valid AC3 Frame.
+ /* initialize the GetBitContext with the start of valid AC-3 Frame */
init_get_bits(&ctx->gb, buf, buf_size * 8);
- //Parse the syncinfo.
+ /* parse the syncinfo */
if (ac3_parse_header(ctx)) {
av_log(avctx, AV_LOG_ERROR, "\n");
*data_size = 0;
@@ -1092,7 +1124,7 @@ static int ac3_decode_frame(AVCodecConte
}
ctx->out_channels = avctx->channels;
- //Parse the Audio Blocks.
+ /* parse the audio blocks */
for (blk = 0; blk < NB_BLOCKS; blk++) {
if (ac3_parse_audio_block(ctx, blk)) {
av_log(avctx, AV_LOG_ERROR, "error parsing the audio block\n");
@@ -1107,7 +1139,8 @@ static int ac3_decode_frame(AVCodecConte
return ctx->frame_size;
}
-/* Uninitialize ac3 decoder.
+/**
+ * Uninitialize the AC-3 decoder.
*/
static int ac3_decode_end(AVCodecContext *avctx)
{
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