The spec states:
* Only the lowest 12 spectral coefficients of any LFE may be non-zero
We were using the 12 lowest *bands*.
---
libavcodec/aacenc.c | 10 +++++++++-
1 files changed, 9 insertions(+), 1 deletions(-)
diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
index e74af0b..7b3794f 100644
--- a/libavcodec/aacenc.c
+++ b/libavcodec/aacenc.c
@@ -540,6 +540,14 @@ static int aac_encode_frame(AVCodecContext *avctx,
wi[ch].window_shape = 0;
wi[ch].num_windows = 1;
wi[ch].grouping[0] = 1;
+
+ /* Only the lowest 12 coefficients are used in a LFE channel */
+ if (s->sample_rate_index >= 11)
+ ics->num_swb = 1;
+ else if (s->sample_rate_index >= 8)
+ ics->num_swb = 2; /* This actually results in 16
coefficients */
+ else
+ ics->num_swb = 3;
} else {
wi[ch] = s->psy.model->window(&s->psy, samples2, la,
cur_channel,
ics->window_sequence[0]);
@@ -550,7 +558,7 @@ static int aac_encode_frame(AVCodecContext *avctx,
ics->use_kb_window[0] = wi[ch].window_shape;
ics->num_windows = wi[ch].num_windows;
ics->swb_sizes = s->psy.bands [ics->num_windows == 8];
- ics->num_swb = tag == TYPE_LFE ? 12 :
s->psy.num_bands[ics->num_windows == 8];
+ ics->num_swb = tag == TYPE_LFE ? ics->num_swb :
s->psy.num_bands[ics->num_windows == 8];
for (w = 0; w < ics->num_windows; w++)
ics->group_len[w] = wi[ch].grouping[w];
--
1.7.4.1
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