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Add spectral extension to the E-AC-3 decoder.

Browse Source 
Original patch by Justin, updated and resubmitted by
Christophe Gisquet, christophe D gisquet A gmail

Originally committed as revision 22734 to svn://svn.ffmpeg.org/ffmpeg/trunk
release/0.6
Carl Eugen Hoyos 15 years ago
parent 1052b76f0f
commit ca6e7708b4
9 changed files with 300 additions and 21 deletions
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  1. 1
      Changelog
  2. 117
      libavcodec/ac3dec.c
  3. 47
      libavcodec/ac3dec.h
  4. 6
      libavcodec/ac3dec_data.c
  5. 1
      libavcodec/ac3dec_data.h
  6. 2
      libavcodec/avcodec.h
  7. 103
      libavcodec/eac3dec.c
  8. 39
      libavcodec/eac3dec_data.c
  9. 1
      libavcodec/eac3dec_data.h

1
Changelog
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@ -68,6 +68,7 @@ version <next>:
- HTTP Digest authentication
- RTMP/RTMPT/RTMPS/RTMPE/RTMPTE protocol support via librtmp
- Psygnosis YOP demuxer and video decoder
- spectral extension support in the E-AC-3 decoder

117
libavcodec/ac3dec.c
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@ -815,14 +815,105 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
/* spectral extension strategy */
if (s->eac3 && (!blk || get_bits1(gbc))) {
if (get_bits1(gbc)) {
av_log_missing_feature(s->avctx, "Spectral extension", 1);
s->spx_in_use = get_bits1(gbc);
if (s->spx_in_use) {
int dst_start_freq, dst_end_freq, src_start_freq,
start_subband, end_subband;
/* determine which channels use spx */
if (s->channel_mode == AC3_CHMODE_MONO) {
s->channel_uses_spx[1] = 1;
} else {
for (ch = 1; ch <= fbw_channels; ch++)
s->channel_uses_spx[ch] = get_bits1(gbc);
}
/* get the frequency bins of the spx copy region and the spx start
and end subbands */
dst_start_freq = get_bits(gbc, 2);
start_subband = get_bits(gbc, 3) + 2;
if (start_subband > 7)
start_subband += start_subband - 7;
end_subband = get_bits(gbc, 3) + 5;
if (end_subband > 7)
end_subband += end_subband - 7;
dst_start_freq = dst_start_freq * 12 + 25;
src_start_freq = start_subband * 12 + 25;
dst_end_freq = end_subband * 12 + 25;
/* check validity of spx ranges */
if (start_subband >= end_subband) {
av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
"range (%d >= %d)\n", start_subband, end_subband);
return -1;
}
/* TODO: parse spectral extension strategy info */
if (dst_start_freq >= src_start_freq) {
av_log(s->avctx, AV_LOG_ERROR, "invalid spectral extension "
"copy start bin (%d >= %d)\n", dst_start_freq, src_start_freq);
return -1;
}
s->spx_dst_start_freq = dst_start_freq;
s->spx_src_start_freq = src_start_freq;
s->spx_dst_end_freq = dst_end_freq;
decode_band_structure(gbc, blk, s->eac3, 0,
start_subband, end_subband,
ff_eac3_default_spx_band_struct,
&s->num_spx_bands,
s->spx_band_sizes);
} else {
for (ch = 1; ch <= fbw_channels; ch++) {
s->channel_uses_spx[ch] = 0;
s->first_spx_coords[ch] = 1;
}
}
}
/* TODO: spectral extension coordinates */
/* spectral extension coordinates */
if (s->spx_in_use) {
for (ch = 1; ch <= fbw_channels; ch++) {
if (s->channel_uses_spx[ch]) {
if (s->first_spx_coords[ch] || get_bits1(gbc)) {
float spx_blend;
int bin, master_spx_coord;
s->first_spx_coords[ch] = 0;
spx_blend = get_bits(gbc, 5) * (1.0f/32);
master_spx_coord = get_bits(gbc, 2) * 3;
bin = s->spx_src_start_freq;
for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
int bandsize;
int spx_coord_exp, spx_coord_mant;
float nratio, sblend, nblend, spx_coord;
/* calculate blending factors */
bandsize = s->spx_band_sizes[bnd];
nratio = ((float)((bin + (bandsize >> 1))) / s->spx_dst_end_freq) - spx_blend;
nratio = av_clipf(nratio, 0.0f, 1.0f);
nblend = sqrtf(3.0f * nratio); // noise is scaled by sqrt(3) to give unity variance
sblend = sqrtf(1.0f - nratio);
bin += bandsize;
/* decode spx coordinates */
spx_coord_exp = get_bits(gbc, 4);
spx_coord_mant = get_bits(gbc, 2);
if (spx_coord_exp == 15) spx_coord_mant <<= 1;
else spx_coord_mant += 4;
spx_coord_mant <<= (25 - spx_coord_exp - master_spx_coord);
spx_coord = spx_coord_mant * (1.0f/(1<<23));
/* multiply noise and signal blending factors by spx coordinate */
s->spx_noise_blend [ch][bnd] = nblend * spx_coord;
s->spx_signal_blend[ch][bnd] = sblend * spx_coord;
}
}
} else {
s->first_spx_coords[ch] = 1;
}
}
}
/* coupling strategy */
if (s->eac3 ? s->cpl_strategy_exists[blk] : get_bits1(gbc)) {
@ -859,9 +950,9 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
s->phase_flags_in_use = get_bits1(gbc);
/* coupling frequency range */
/* TODO: modify coupling end freq if spectral extension is used */
cpl_start_subband = get_bits(gbc, 4);
cpl_end_subband = get_bits(gbc, 4) + 3;
cpl_end_subband = s->spx_in_use ? (s->spx_src_start_freq - 37) / 12 :
get_bits(gbc, 4) + 3;
if (cpl_start_subband >= cpl_end_subband) {
av_log(s->avctx, AV_LOG_ERROR, "invalid coupling range (%d >= %d)\n",
cpl_start_subband, cpl_end_subband);
@ -934,8 +1025,11 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
if (channel_mode == AC3_CHMODE_STEREO) {
if ((s->eac3 && !blk) || get_bits1(gbc)) {
s->num_rematrixing_bands = 4;
if(cpl_in_use && s->start_freq[CPL_CH] <= 61)
if (cpl_in_use && s->start_freq[CPL_CH] <= 61) {
s->num_rematrixing_bands -= 1 + (s->start_freq[CPL_CH] == 37);
} else if (s->spx_in_use && s->spx_src_start_freq <= 61) {
s->num_rematrixing_bands--;
}
for(bnd=0; bnd<s->num_rematrixing_bands; bnd++)
s->rematrixing_flags[bnd] = get_bits1(gbc);
} else if (!blk) {
@ -960,6 +1054,8 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
int prev = s->end_freq[ch];
if (s->channel_in_cpl[ch])
s->end_freq[ch] = s->start_freq[CPL_CH];
else if (s->channel_uses_spx[ch])
s->end_freq[ch] = s->spx_src_start_freq;
else {
int bandwidth_code = get_bits(gbc, 6);
if (bandwidth_code > 60) {
@ -1156,8 +1252,6 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
/* TODO: generate enhanced coupling coordinates and uncouple */
/* TODO: apply spectral extension */
/* recover coefficients if rematrixing is in use */
if(s->channel_mode == AC3_CHMODE_STEREO)
do_rematrixing(s);
@ -1173,6 +1267,11 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
s->dsp.int32_to_float_fmul_scalar(s->transform_coeffs[ch], s->fixed_coeffs[ch], gain, 256);
}
/* apply spectral extension to high frequency bins */
if (s->spx_in_use) {
ff_eac3_apply_spectral_extension(s);
}
/* downmix and MDCT. order depends on whether block switching is used for
any channel in this block. this is because coefficients for the long
and short transforms cannot be mixed. */

47
libavcodec/ac3dec.h
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@ -22,6 +22,29 @@
/**
* @file libavcodec/ac3.h
* Common code between the AC-3 and E-AC-3 decoders.
*
* Summary of MDCT Coefficient Grouping:
* The individual MDCT coefficient indices are often referred to in the
* (E-)AC-3 specification as frequency bins. These bins are grouped together
* into subbands of 12 coefficients each. The subbands are grouped together
* into bands as defined in the bitstream by the band structures, which
* determine the number of bands and the size of each band. The full spectrum
* of 256 frequency bins is divided into 1 DC bin + 21 subbands = 253 bins.
* This system of grouping coefficients is used for channel bandwidth, stereo
* rematrixing, channel coupling, enhanced coupling, and spectral extension.
*
* +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
* |1| |12| | [12|12|12|12] | | | | | | | | | | | | |3|
* +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
* ~~~ ~~~~ ~~~~~~~~~~~~~ ~~~
* | | | |
* | | | 3 unused frequency bins--+
* | | |
* | | +--1 band containing 4 subbands
* | |
* | +--1 subband of 12 frequency bins
* |
* +--DC frequency bin
*/
#ifndef AVCODEC_AC3DEC_H
@ -43,6 +66,7 @@
#define AC3_MAX_COEFS 256
#define AC3_BLOCK_SIZE 256
#define MAX_BLOCKS 6
#define SPX_MAX_BANDS 17
typedef struct {
AVCodecContext *avctx; ///< parent context
@ -89,6 +113,22 @@ typedef struct {
int cpl_coords[AC3_MAX_CHANNELS][18]; ///< coupling coordinates (cplco)
///@}
///@defgroup spx spectral extension
///@{
int spx_in_use; ///< spectral extension in use (spxinu)
uint8_t channel_uses_spx[AC3_MAX_CHANNELS]; ///< channel uses spectral extension (chinspx)
int8_t spx_atten_code[AC3_MAX_CHANNELS]; ///< spx attenuation code (spxattencod)
int spx_src_start_freq; ///< spx start frequency bin
int spx_dst_end_freq; ///< spx end frequency bin
int spx_dst_start_freq; ///< spx starting frequency bin for copying (copystartmant)
///< the copy region ends at the start of the spx region.
int num_spx_bands; ///< number of spx bands (nspxbnds)
uint8_t spx_band_sizes[SPX_MAX_BANDS]; ///< number of bins in each spx band
uint8_t first_spx_coords[AC3_MAX_CHANNELS]; ///< first spx coordinates states (firstspxcos)
float spx_noise_blend[AC3_MAX_CHANNELS][SPX_MAX_BANDS]; ///< spx noise blending factor (nblendfact)
float spx_signal_blend[AC3_MAX_CHANNELS][SPX_MAX_BANDS];///< spx signal blending factor (sblendfact)
///@}
///@defgroup aht adaptive hybrid transform
int channel_uses_aht[AC3_MAX_CHANNELS]; ///< channel AHT in use (chahtinu)
int pre_mantissa[AC3_MAX_CHANNELS][AC3_MAX_COEFS][MAX_BLOCKS]; ///< pre-IDCT mantissas
@ -182,4 +222,11 @@ void ff_eac3_decode_transform_coeffs_aht_ch(AC3DecodeContext *s, int ch);
void ff_ac3_downmix_c(float (*samples)[256], float (*matrix)[2],
int out_ch, int in_ch, int len);
/**
* Apply spectral extension to each channel by copying lower frequency
* coefficients to higher frequency bins and applying side information to
* approximate the original high frequency signal.
*/
void ff_eac3_apply_spectral_extension(AC3DecodeContext *s);
#endif /* AVCODEC_AC3DEC_H */

6
libavcodec/ac3dec_data.c
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@ -64,3 +64,9 @@ const uint8_t ff_eac3_hebap_tab[64] = {
*/
const uint8_t ff_eac3_default_cpl_band_struct[18] =
{ 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1 };
/**
* Table E2.15 Default Spectral Extension Banding Structure
*/
const uint8_t ff_eac3_default_spx_band_struct[17] =
{ 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1 };

1
libavcodec/ac3dec_data.h
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@ -29,5 +29,6 @@ extern const uint8_t ff_ac3_rematrix_band_tab[5];
extern const uint8_t ff_eac3_hebap_tab[64];
extern const uint8_t ff_eac3_default_cpl_band_struct[18];
extern const uint8_t ff_eac3_default_spx_band_struct[17];
#endif /* AVCODEC_AC3DEC_DATA_H */

2
libavcodec/avcodec.h
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@ -30,7 +30,7 @@
#include "libavutil/avutil.h"
#define LIBAVCODEC_VERSION_MAJOR 52
#define LIBAVCODEC_VERSION_MINOR 62
#define LIBAVCODEC_VERSION_MINOR 63
#define LIBAVCODEC_VERSION_MICRO 0
#define LIBAVCODEC_VERSION_INT AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \

103
libavcodec/eac3dec.c
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@ -23,10 +23,6 @@
/*
* There are several features of E-AC-3 that this decoder does not yet support.
*
* Spectral Extension
* There is a patch to get this working for the two samples we have that
* use it, but it needs some minor changes in order to be accepted.
*
* Enhanced Coupling
* No known samples exist. If any ever surface, this feature should not be
* too difficult to implement.
@ -67,6 +63,95 @@ typedef enum {
#define EAC3_SR_CODE_REDUCED 3
void ff_eac3_apply_spectral_extension(AC3DecodeContext *s)
{
int bin, bnd, ch, i;
uint8_t wrapflag[SPX_MAX_BANDS]={1,0,}, num_copy_sections, copy_sizes[SPX_MAX_BANDS];
float rms_energy[SPX_MAX_BANDS];
/* Set copy index mapping table. Set wrap flags to apply a notch filter at
wrap points later on. */
bin = s->spx_dst_start_freq;
num_copy_sections = 0;
for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
int copysize;
int bandsize = s->spx_band_sizes[bnd];
if (bin + bandsize > s->spx_src_start_freq) {
copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq;
bin = s->spx_dst_start_freq;
wrapflag[bnd] = 1;
}
for (i = 0; i < bandsize; i += copysize) {
if (bin == s->spx_src_start_freq) {
copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq;
bin = s->spx_dst_start_freq;
}
copysize = FFMIN(bandsize - i, s->spx_src_start_freq - bin);
bin += copysize;
}
}
copy_sizes[num_copy_sections++] = bin - s->spx_dst_start_freq;
for (ch = 1; ch <= s->fbw_channels; ch++) {
if (!s->channel_uses_spx[ch])
continue;
/* Copy coeffs from normal bands to extension bands */
bin = s->spx_src_start_freq;
for (i = 0; i < num_copy_sections; i++) {
memcpy(&s->transform_coeffs[ch][bin],
&s->transform_coeffs[ch][s->spx_dst_start_freq],
copy_sizes[i]*sizeof(float));
bin += copy_sizes[i];
}
/* Calculate RMS energy for each SPX band. */
bin = s->spx_src_start_freq;
for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
int bandsize = s->spx_band_sizes[bnd];
float accum = 0.0f;
for (i = 0; i < bandsize; i++) {
float coeff = s->transform_coeffs[ch][bin++];
accum += coeff * coeff;
}
rms_energy[bnd] = sqrtf(accum / bandsize);
}
/* Apply a notch filter at transitions between normal and extension
bands and at all wrap points. */
if (s->spx_atten_code[ch] >= 0) {
const float *atten_tab = ff_eac3_spx_atten_tab[s->spx_atten_code[ch]];
bin = s->spx_src_start_freq - 2;
for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
if (wrapflag[bnd]) {
float *coeffs = &s->transform_coeffs[ch][bin];
coeffs[0] *= atten_tab[0];
coeffs[1] *= atten_tab[1];
coeffs[2] *= atten_tab[2];
coeffs[3] *= atten_tab[1];
coeffs[4] *= atten_tab[0];
}
bin += s->spx_band_sizes[bnd];
}
}
/* Apply noise-blended coefficient scaling based on previously
calculated RMS energy, blending factors, and SPX coordinates for
each band. */
bin = s->spx_src_start_freq;
for (bnd = 0; bnd < s->num_spx_bands; bnd++) {
float nscale = s->spx_noise_blend[ch][bnd] * rms_energy[bnd] * (1.0f/(1<<31));
float sscale = s->spx_signal_blend[ch][bnd];
for (i = 0; i < s->spx_band_sizes[bnd]; i++) {
float noise = nscale * (int32_t)av_lfg_get(&s->dith_state);
s->transform_coeffs[ch][bin] *= sscale;
s->transform_coeffs[ch][bin++] += noise;
}
}
}
}
/** lrint(M_SQRT2*cos(2*M_PI/12)*(1<<23)) */
#define COEFF_0 10273905LL
@ -492,12 +577,11 @@ int ff_eac3_parse_header(AC3DecodeContext *s)
}
/* spectral extension attenuation data */
if (parse_spx_atten_data) {
av_log_missing_feature(s->avctx, "Spectral extension attenuation", 1);
for (ch = 1; ch <= s->fbw_channels; ch++) {
if (get_bits1(gbc)) { // channel has spx attenuation
skip_bits(gbc, 5); // skip spx attenuation code
}
if (parse_spx_atten_data && get_bits1(gbc)) {
s->spx_atten_code[ch] = get_bits(gbc, 5);
} else {
s->spx_atten_code[ch] = -1;
}
}
@ -514,6 +598,7 @@ int ff_eac3_parse_header(AC3DecodeContext *s)
/* syntax state initialization */
for (ch = 1; ch <= s->fbw_channels; ch++) {
s->first_spx_coords[ch] = 1;
s->first_cpl_coords[ch] = 1;
}
s->first_cpl_leak = 1;

39
libavcodec/eac3dec_data.c
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@ -1093,3 +1093,42 @@ const uint8_t ff_eac3_frm_expstr[32][6] = {
{ EXP_D45, EXP_D45, EXP_D45, EXP_D45, EXP_D25, EXP_REUSE},
{ EXP_D45, EXP_D45, EXP_D45, EXP_D45, EXP_D45, EXP_D45},
};
/**
* Table E.25: Spectral Extension Attenuation Table
* ff_eac3_spx_atten_tab[code][bin]=pow(2.0,(bin+1)*(code+1)/-15.0);
*/
const float ff_eac3_spx_atten_tab[32][3] = {
{ 0.954841603910416503f, 0.911722488558216804f, 0.870550563296124125f },
{ 0.911722488558216804f, 0.831237896142787758f, 0.757858283255198995f },
{ 0.870550563296124125f, 0.757858283255198995f, 0.659753955386447100f },
{ 0.831237896142787758f, 0.690956439983888004f, 0.574349177498517438f },
{ 0.793700525984099792f, 0.629960524947436595f, 0.500000000000000000f },
{ 0.757858283255198995f, 0.574349177498517438f, 0.435275281648062062f },
{ 0.723634618720189082f, 0.523647061410313364f, 0.378929141627599553f },
{ 0.690956439983888004f, 0.477420801955208307f, 0.329876977693223550f },
{ 0.659753955386447100f, 0.435275281648062062f, 0.287174588749258719f },
{ 0.629960524947436595f, 0.396850262992049896f, 0.250000000000000000f },
{ 0.601512518041058319f, 0.361817309360094541f, 0.217637640824031003f },
{ 0.574349177498517438f, 0.329876977693223550f, 0.189464570813799776f },
{ 0.548412489847312945f, 0.300756259020529160f, 0.164938488846611775f },
{ 0.523647061410313364f, 0.274206244923656473f, 0.143587294374629387f },
{ 0.500000000000000000f, 0.250000000000000000f, 0.125000000000000000f },
{ 0.477420801955208307f, 0.227930622139554201f, 0.108818820412015502f },
{ 0.455861244279108402f, 0.207809474035696939f, 0.094732285406899888f },
{ 0.435275281648062062f, 0.189464570813799776f, 0.082469244423305887f },
{ 0.415618948071393879f, 0.172739109995972029f, 0.071793647187314694f },
{ 0.396850262992049896f, 0.157490131236859149f, 0.062500000000000000f },
{ 0.378929141627599553f, 0.143587294374629387f, 0.054409410206007751f },
{ 0.361817309360094541f, 0.130911765352578369f, 0.047366142703449930f },
{ 0.345478219991944002f, 0.119355200488802049f, 0.041234622211652958f },
{ 0.329876977693223550f, 0.108818820412015502f, 0.035896823593657347f },
{ 0.314980262473718298f, 0.099212565748012460f, 0.031250000000000000f },
{ 0.300756259020529160f, 0.090454327340023621f, 0.027204705103003875f },
{ 0.287174588749258719f, 0.082469244423305887f, 0.023683071351724965f },
{ 0.274206244923656473f, 0.075189064755132290f, 0.020617311105826479f },
{ 0.261823530705156682f, 0.068551561230914118f, 0.017948411796828673f },
{ 0.250000000000000000f, 0.062500000000000000f, 0.015625000000000000f },
{ 0.238710400977604098f, 0.056982655534888536f, 0.013602352551501938f },
{ 0.227930622139554201f, 0.051952368508924235f, 0.011841535675862483f }
};

1
libavcodec/eac3dec_data.h
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@ -31,5 +31,6 @@ extern const int16_t ff_eac3_gaq_remap_2_4_b[9][2];
extern const int16_t (* const ff_eac3_mantissa_vq[8])[6];
extern const uint8_t ff_eac3_frm_expstr[32][6];
extern const float ff_eac3_spx_atten_tab[32][3];
#endif /* AVCODEC_EAC3DEC_DATA_H */

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