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aacenc: Fix number of coefficients used in a LFE channel.

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The spec states:

 *  Only the lowest 12 spectral coefficients of any LFE may be non-zero

We were using the 12 lowest *bands*.
This commit is contained in:
Nathan Caldwell 2011-07-29 14:49:04 -06:00 committed by Alex Converse
parent 51a1d4d94a
commit 24efdea7fd
1 changed files with 7 additions and 1 deletions
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8
libavcodec/aacenc.c
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@ -540,6 +540,12 @@ 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.
* The expression below results in only the bottom 8 coefficients
* being used for 11.025kHz to 16kHz sample rates.
*/
ics->num_swb = s->samplerate_index >= 8 ? 1 : 3;
} else {
wi[ch] = s->psy.model->window(&s->psy, samples2, la, cur_channel,
ics->window_sequence[0]);
@ -550,7 +556,7 @@ 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];