This commit implements support for writing the noise energy values used in PNS.
The difference between regular scalefactors and noise energy values is that the
latter require a small preamble (NOISE_PRE + energy_value_diff) to be written
as the first noise-containing band. Any following noise energy values use the
previous one to base their "diff" on. Ordinary scalefactors remain unchanged
other than that they ignore the noise values.
This commit should not change anything by itself, the following commits will
bring it in use.
---
libavcodec/aac.h | 3 +++
libavcodec/aacenc.c | 17 ++++++++++++++---
2 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/libavcodec/aac.h b/libavcodec/aac.h
index b25b40c..2701386 100644
--- a/libavcodec/aac.h
+++ b/libavcodec/aac.h
@@ -141,6 +141,9 @@ typedef struct PredictorState {
#define SCALE_MAX_DIFF 60 ///< maximum scalefactor difference allowed by
standard
#define SCALE_DIFF_ZERO 60 ///< codebook index corresponding to zero
scalefactor indices difference
+#define NOISE_PRE 256 ///< preamble for NOISE_BT, put in bitstream
with the first noise band
+#define NOISE_PRE_BITS 9 ///< length of preamble
+
/**
* Long Term Prediction
*/
diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
index 7015a27..5288afb 100644
--- a/libavcodec/aacenc.c
+++ b/libavcodec/aacenc.c
@@ -388,15 +388,26 @@ static void encode_band_info(AACEncContext *s,
SingleChannelElement *sce)
static void encode_scale_factors(AVCodecContext *avctx, AACEncContext *s,
SingleChannelElement *sce)
{
- int off = sce->sf_idx[0], diff;
+ int diff, off_sf = sce->sf_idx[0], off_pns = sce->sf_idx[0];
+ int noise_flag = 1;
int i, w;
for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
for (i = 0; i < sce->ics.max_sfb; i++) {
if (!sce->zeroes[w*16 + i]) {
- diff = sce->sf_idx[w*16 + i] - off + SCALE_DIFF_ZERO;
+ if (sce->band_type[w*16 + i] == NOISE_BT) {
+ diff = sce->sf_idx[w*16 + i] - off_pns;
+ off_pns = sce->sf_idx[w*16 + i];
+ if (noise_flag-- > 0) {
+ put_bits(&s->pb, NOISE_PRE_BITS, diff + NOISE_PRE);
+ continue;
+ }
+ } else {
+ diff = sce->sf_idx[w*16 + i] - off_sf;
+ off_sf = sce->sf_idx[w*16 + i];
+ }
+ diff += SCALE_DIFF_ZERO;
av_assert0(diff >= 0 && diff <= 120);
- off = sce->sf_idx[w*16 + i];
put_bits(&s->pb, ff_aac_scalefactor_bits[diff],
ff_aac_scalefactor_code[diff]);
}
}
--
2.1.4
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