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aacenc_tns: clamp filter direction energy measurement

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The issue is that:

float en[2];
...
tns->n_filt[w] = is8 ? 1 : order != TNS_MAX_ORDER ? 2 : 3;
for (g = 0; g < tns->n_filt[w]; g++) {
    tns->direction[w][g] = slant != 2 ? slant : en[g] < en[!g];

When using the AAC Main profile, n_filt = 3, and slant is by
default 2 (normal long frames), g can go above 1.

en is the evolution of energy in the frequency domain for every
band at the given window. E.g. whether the energy is concentrated
at the top of each band, or the bottom.

For 2-pole filters, its straightforward.
For 3-pole filters, we need more than 2 measurements.

This commit properly implements support for 3-pole filters, by measuring
the band energy across three areas.

Do note that even xHE-AAC caps n_filt to 2, and only AAC Main allows
n_filt == 3.

Fixes https://trac.ffmpeg.org/ticket/11418

(cherry picked from commit ed09aa28ae3b4509f00a24a9ebdeb084ee00736a)
This commit is contained in:
Lynne
2025-02-08 04:35:31 +01:00
parent 2e503a9b94
commit f98f142da5
1 changed files with 27 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

40
libavcodec/aacenc_tns.c
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@@ -173,6 +173,7 @@ void ff_aac_search_for_tns(AACEncContext *s, SingleChannelElement *sce)
sce->ics.window_sequence[0] == LONG_START_SEQUENCE ? 0 : 2;
const int sfb_len = sfb_end - sfb_start;
const int coef_len = sce->ics.swb_offset[sfb_end] - sce->ics.swb_offset[sfb_start];
const int n_filt = is8 ? 1 : order != TNS_MAX_ORDER ? 2 : 3;
if (coef_len <= 0 || sfb_len <= 0) {
sce->tns.present = 0;
@@ -180,16 +181,30 @@ void ff_aac_search_for_tns(AACEncContext *s, SingleChannelElement *sce)
}
for (w = 0; w < sce->ics.num_windows; w++) {
float en[2] = {0.0f, 0.0f};
int oc_start = 0, os_start = 0;
float en[4] = {0.0f, 0.0f, 0.0f, 0.0f};
int oc_start = 0;
int coef_start = sce->ics.swb_offset[sfb_start];
for (g = sfb_start; g < sce->ics.num_swb && g <= sfb_end; g++) {
FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[w*16+g];
if (g > sfb_start + (sfb_len/2))
en[1] += band->energy;
else
en[0] += band->energy;
if (n_filt == 2) {
for (g = sfb_start; g < sce->ics.num_swb && g <= sfb_end; g++) {
FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[w*16+g];
if (g > sfb_start + (sfb_len/2))
en[1] += band->energy; /* End */
else
en[0] += band->energy; /* Start */
}
en[2] = en[0];
} else {
for (g = sfb_start; g < sce->ics.num_swb && g <= sfb_end; g++) {
FFPsyBand *band = &s->psy.ch[s->cur_channel].psy_bands[w*16+g];
if (g > sfb_start + (sfb_len/2) + (sfb_len/4))
en[2] += band->energy; /* End */
else if (g > sfb_start + (sfb_len/2) - (sfb_len/4))
en[1] += band->energy; /* Middle */
else
en[0] += band->energy; /* Start */
}
en[3] = en[0];
}
/* LPC */
@@ -199,15 +214,14 @@ void ff_aac_search_for_tns(AACEncContext *s, SingleChannelElement *sce)
if (!order || !isfinite(gain) || gain < TNS_GAIN_THRESHOLD_LOW || gain > TNS_GAIN_THRESHOLD_HIGH)
continue;
tns->n_filt[w] = is8 ? 1 : order != TNS_MAX_ORDER ? 2 : 3;
tns->n_filt[w] = n_filt;
for (g = 0; g < tns->n_filt[w]; g++) {
tns->direction[w][g] = slant != 2 ? slant : en[g] < en[!g];
tns->order[w][g] = g < tns->n_filt[w] ? order/tns->n_filt[w] : order - oc_start;
tns->length[w][g] = g < tns->n_filt[w] ? sfb_len/tns->n_filt[w] : sfb_len - os_start;
tns->direction[w][g] = slant != 2 ? slant : en[g] < en[g + 1];
tns->order[w][g] = order/tns->n_filt[w];
tns->length[w][g] = sfb_len/tns->n_filt[w];
quantize_coefs(&coefs[oc_start], tns->coef_idx[w][g], tns->coef[w][g],
tns->order[w][g], c_bits);
oc_start += tns->order[w][g];
os_start += tns->length[w][g];
}
count++;
}