This commit implements intensity stereo coding support to the native aac
encoder. This is a way to increase the efficiency of the encoder by zeroing the
right channel's spectral coefficients (in a channel pair) and rederiving them
in the decoder using information from the scalefactor indices of special band
types. This commit confomrs to the official ISO 13818-7 specifications,
although due to their ambiguity certain deviations have been taken to ensure
maximum sound quality. This commit has been extensively tested and has shown to
not result in audiable audio artifacts unless in extreme cases. This commit
also adds an option, aac_is, which has the value of 0 by default. Intensity
Stereo is part of the scalable aac profile and is thus non-default.
The way IS coding works is that it rederives the right channel's spectral
coefficients from the left channel via the scalefactor index values left in the
right channel. Since an entire band's spectral coefficients do not need to be
coded, the encoder's efficiency jumps up and it unzeroes some high frequency
values which it previously did not have enough bits to encode. That way less
information is lost than the information lost by rederiving the spectral
coefficients with some error. This is why the filesize of files encoded with IS
do not decrease significantly. Users wishing that IS coding should reduce
filesize are expected to reduce their encoding bitrates appropriately.
This is V2 of the commit. The old version did not mark ms_mask as 0 since M/S
and IS coding are incompactible, which resulted in distortions with M/S coding
enabled. This version also improves phase detection by measuring it for every
spectral coefficient in the band and using a simple majority rule to determine
whether the coefficients are in or out of phase. Also, the energy values per
spectral coefficient were changed as to reflect the official specifications.
---
libavcodec/aaccoder.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++++-
libavcodec/aacenc.c | 11 +++++-
libavcodec/aacenc.h | 2 +
3 files changed, 117 insertions(+), 3 deletions(-)
diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index 95782fc..5bdba46 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -52,6 +52,9 @@
* excessive PNS and little PNS usage. */
#define NOISE_LAMBDA_NUMERATOR 252.1f
+/** Frequency in Hz for lower limit of intensity stereo **/
+#define INT_STEREO_LOW_LIMIT 6100
+
/** Total number of usable codebooks **/
#define CB_TOT 12
@@ -1178,6 +1181,104 @@ static void search_for_pns(AACEncContext *s,
AVCodecContext *avctx, SingleChanne
}
}
+static void search_for_is(AACEncContext *s, AVCodecContext *avctx,
ChannelElement *cpe,
+ const float lambda)
+{
+ float IS[128];
+ float *L34 = s->scoefs + 128*0, *R34 = s->scoefs + 128*1;
+ float *I34 = s->scoefs + 128*2;
+ SingleChannelElement *sce0 = &cpe->ch[0];
+ SingleChannelElement *sce1 = &cpe->ch[1];
+ int start = 0, count = 0, i, w, w2, g;
+ const float freq_mult =
avctx->sample_rate/(1024.0f/sce0->ics.num_windows)/2.0f;
+
+ for (w = 0; w < 128; w++)
+ if (sce1->band_type[w] >= INTENSITY_BT2)
+ sce1->band_type[w] = 0;
+
+ if (!cpe->common_window)
+ return;
+ for (w = 0; w < sce0->ics.num_windows; w += sce0->ics.group_len[w]) {
+ start = 0;
+ for (g = 0; g < sce0->ics.num_swb; g++) {
+ if (start*freq_mult > INT_STEREO_LOW_LIMIT*(lambda/170.0f) &&
+ cpe->ch[0].band_type[w*16+g] != NOISE_BT &&
!cpe->ch[0].zeroes[w*16+g] &&
+ cpe->ch[1].band_type[w*16+g] != NOISE_BT &&
!cpe->ch[1].zeroes[w*16+g]) {
+ int phase = 0;
+ float ener0 = 0.0f, ener1 = 0.0f, ener01 = 0.0f;
+ float dist1 = 0.0f, dist2 = 0.0f;
+ for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
+ for (i = 0; i < sce0->ics.swb_sizes[g]; i++) {
+ float coef0 = sce0->pcoeffs[start+(w+w2)*128+i];
+ float coef1 = sce1->pcoeffs[start+(w+w2)*128+i];
+ phase += coef0*coef1 >= 0.0f ? 1 : -1;
+ ener0 += coef0*coef0;
+ ener1 += coef1*coef1;
+ ener01 += (coef0 + coef1)*(coef0 + coef1);
+ }
+ }
+ if (!phase) { /* Too much phase difference between channels */
+ start += sce0->ics.swb_sizes[g];
+ continue;
+ }
+ phase = av_clip(phase, -1, 1);
+ for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
+ FFPsyBand *band0 =
&s->psy.ch[s->cur_channel+0].psy_bands[(w+w2)*16+g];
+ FFPsyBand *band1 =
&s->psy.ch[s->cur_channel+1].psy_bands[(w+w2)*16+g];
+ int is_band_type, is_sf_idx = FFMAX(1,
sce0->sf_idx[(w+w2)*16+g]-4);
+ float e01_34 = phase*pow(sqrt(ener1/ener0), 3.0/4.0);
+ float maxval, dist_spec_err = 0.0f;
+ float minthr = FFMIN(band0->threshold, band1->threshold);
+ for (i = 0; i < sce0->ics.swb_sizes[g]; i++)
+ IS[i] = (sce0->pcoeffs[start+(w+w2)*128+i] +
phase*sce1->pcoeffs[start+(w+w2)*128+i]) * sqrt(ener0/ener01);
+ abs_pow34_v(L34, sce0->coeffs+start+(w+w2)*128,
sce0->ics.swb_sizes[g]);
+ abs_pow34_v(R34, sce1->coeffs+start+(w+w2)*128,
sce0->ics.swb_sizes[g]);
+ abs_pow34_v(I34, IS,
sce0->ics.swb_sizes[g]);
+ maxval = find_max_val(1, sce0->ics.swb_sizes[g], I34);
+ is_band_type = find_min_book(maxval, is_sf_idx);
+ dist1 += quantize_band_cost(s, sce0->coeffs + start +
(w+w2)*128,
+ L34,
+ sce0->ics.swb_sizes[g],
+ sce0->sf_idx[(w+w2)*16+g],
+ sce0->band_type[(w+w2)*16+g],
+ lambda / band0->threshold,
INFINITY, NULL);
+ dist1 += quantize_band_cost(s, sce1->coeffs + start +
(w+w2)*128,
+ R34,
+ sce1->ics.swb_sizes[g],
+ sce1->sf_idx[(w+w2)*16+g],
+ sce1->band_type[(w+w2)*16+g],
+ lambda / band1->threshold,
INFINITY, NULL);
+ dist2 += quantize_band_cost(s, IS,
+ I34,
+ sce0->ics.swb_sizes[g],
+ is_sf_idx,
+ is_band_type,
+ lambda / minthr, INFINITY,
NULL);
+ for (i = 0; i < sce0->ics.swb_sizes[g]; i++) {
+ dist_spec_err += (L34[i] - I34[i])*(L34[i] - I34[i]);
+ dist_spec_err += (R34[i] - I34[i]*e01_34)*(R34[i] -
I34[i]*e01_34);
+ }
+ dist_spec_err *= lambda / minthr;
+ dist2 += dist_spec_err;
+ }
+ if (dist2 <= dist1) {
+ cpe->is_mask[w*16+g] = 1;
+ cpe->ms_mask[w*16+g] = 0;
+ cpe->ch[0].is_ener[w*16+g] = sqrt(ener0/ener01);
+ cpe->ch[1].is_ener[w*16+g] = ener0/ener1;
+ if (phase)
+ cpe->ch[1].band_type[w*16+g] = INTENSITY_BT;
+ else
+ cpe->ch[1].band_type[w*16+g] = INTENSITY_BT2;
+ count++;
+ }
+ }
+ start += sce0->ics.swb_sizes[g];
+ }
+ }
+ cpe->is_mode = !!count;
+}
+
static void search_for_ms(AACEncContext *s, ChannelElement *cpe,
const float lambda)
{
@@ -1191,7 +1292,7 @@ static void search_for_ms(AACEncContext *s,
ChannelElement *cpe,
for (w = 0; w < sce0->ics.num_windows; w += sce0->ics.group_len[w]) {
start = 0;
for (g = 0; g < sce0->ics.num_swb; g++) {
- if (!cpe->ch[0].zeroes[w*16+g] && !cpe->ch[1].zeroes[w*16+g]) {
+ if (!cpe->ch[0].zeroes[w*16+g] && !cpe->ch[1].zeroes[w*16+g] &&
!cpe->is_mask[w*16+g]) {
float dist1 = 0.0f, dist2 = 0.0f;
for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
FFPsyBand *band0 =
&s->psy.ch[s->cur_channel+0].psy_bands[(w+w2)*16+g];
@@ -1248,6 +1349,7 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
set_special_band_scalefactors,
search_for_pns,
search_for_ms,
+ search_for_is,
},
[AAC_CODER_ANMR] = {
search_for_quantizers_anmr,
@@ -1256,6 +1358,7 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
set_special_band_scalefactors,
search_for_pns,
search_for_ms,
+ search_for_is,
},
[AAC_CODER_TWOLOOP] = {
search_for_quantizers_twoloop,
@@ -1264,6 +1367,7 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
set_special_band_scalefactors,
search_for_pns,
search_for_ms,
+ search_for_is,
},
[AAC_CODER_FAST] = {
search_for_quantizers_fast,
@@ -1272,5 +1376,6 @@ AACCoefficientsEncoder ff_aac_coders[AAC_CODER_NB] = {
set_special_band_scalefactors,
search_for_pns,
search_for_ms,
+ search_for_is,
},
};
diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
index 3e5ac72..a4248ff 100644
--- a/libavcodec/aacenc.c
+++ b/libavcodec/aacenc.c
@@ -550,7 +550,7 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket
*avpkt,
AACEncContext *s = avctx->priv_data;
float **samples = s->planar_samples, *samples2, *la, *overlap;
ChannelElement *cpe;
- int i, ch, w, g, chans, tag, start_ch, ret, ms_mode = 0;
+ int i, ch, w, g, chans, tag, start_ch, ret, ms_mode = 0, is_mode = 0;
int chan_el_counter[4];
FFPsyWindowInfo windows[AAC_MAX_CHANNELS];
@@ -675,6 +675,10 @@ static int aac_encode_frame(AVCodecContext *avctx,
AVPacket *avpkt,
s->coder->search_for_ms(s, cpe, s->lambda);
}
}
+ if (chans > 1 && s->options.intensity_stereo &&
s->coder->search_for_is) {
+ s->coder->search_for_is(s, avctx, cpe, s->lambda);
+ if (cpe->is_mode) is_mode = 1;
+ }
if (s->coder->set_special_band_scalefactors)
for (ch = 0; ch < chans; ch++)
s->coder->set_special_band_scalefactors(s, &cpe->ch[ch]);
@@ -699,7 +703,7 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket
*avpkt,
s->psy.bitres.bits = frame_bits / s->channels;
break;
}
- if (ms_mode) {
+ if (is_mode || ms_mode) {
for (i = 0; i < s->chan_map[0]; i++) {
// Must restore coeffs
chans = tag == TYPE_CPE ? 2 : 1;
@@ -877,6 +881,9 @@ static const AVOption aacenc_options[] = {
{"aac_pns", "Perceptual Noise Substitution", offsetof(AACEncContext,
options.pns), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, AACENC_FLAGS, "aac_pns"},
{"disable", "Disable PNS", 0, AV_OPT_TYPE_CONST, {.i64 = 0 },
INT_MIN, INT_MAX, AACENC_FLAGS, "aac_pns"},
{"enable", "Enable PNS (Proof of concept)", 0, AV_OPT_TYPE_CONST,
{.i64 = 1 }, INT_MIN, INT_MAX, AACENC_FLAGS, "aac_pns"},
+ {"aac_is", "Intensity stereo coding", offsetof(AACEncContext,
options.intensity_stereo), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, AACENC_FLAGS,
"intensity_stereo"},
+ {"disable", "Disable intensity stereo coding", 0, AV_OPT_TYPE_CONST,
{.i64 = 0}, INT_MIN, INT_MAX, AACENC_FLAGS, "intensity_stereo"},
+ {"enable", "Enable intensity stereo coding", 0, AV_OPT_TYPE_CONST,
{.i64 = 1}, INT_MIN, INT_MAX, AACENC_FLAGS, "intensity_stereo"},
{NULL}
};
diff --git a/libavcodec/aacenc.h b/libavcodec/aacenc.h
index 8ba5817..966c708 100644
--- a/libavcodec/aacenc.h
+++ b/libavcodec/aacenc.h
@@ -43,6 +43,7 @@ typedef struct AACEncOptions {
int stereo_mode;
int aac_coder;
int pns;
+ int intensity_stereo;
} AACEncOptions;
struct AACEncContext;
@@ -57,6 +58,7 @@ typedef struct AACCoefficientsEncoder {
void (*set_special_band_scalefactors)(struct AACEncContext *s,
SingleChannelElement *sce);
void (*search_for_pns)(struct AACEncContext *s, AVCodecContext *avctx,
SingleChannelElement *sce, const float lambda);
void (*search_for_ms)(struct AACEncContext *s, ChannelElement *cpe, const
float lambda);
+ void (*search_for_is)(struct AACEncContext *s, AVCodecContext *avctx,
ChannelElement *cpe, const float lambda);
} AACCoefficientsEncoder;
extern AACCoefficientsEncoder ff_aac_coders[];
--
2.1.4
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