[FFmpeg-devel] [PATCH v2 2/3] [GSoC] [AAC] aacenc: Adjust the initial offset for PNS values

[Rostislav Pehlivanov]

This commit adjusts the intial offset for PNS values, introduced with commit f7f71b5795d708763eb0c55fe5e2cb051b2b69f4 earlier. This commit shifts the value in such a way that no further offsets are required in the aaccoder.c file. Earlier version of the PNS patch had 2 offsets in both the aaccoder and aacenc.
---
 libavcodec/aac.h    | 1 +
 libavcodec/aacenc.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavcodec/aac.h b/libavcodec/aac.h
index 2701386..23ec085 100644
--- a/libavcodec/aac.h
+++ b/libavcodec/aac.h
@@ -143,6 +143,7 @@ typedef struct PredictorState {
 
 #define NOISE_PRE       256    ///< preamble for NOISE_BT, put in bitstream with the first noise band
 #define NOISE_PRE_BITS    9    ///< length of preamble
+#define NOISE_OFFSET     90    ///< subtracted from global gain, used as offset for the preamble
 
 /**
  * Long Term Prediction
diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
index 3e92bc4..998a875 100644
--- a/libavcodec/aacenc.c
+++ b/libavcodec/aacenc.c
@@ -388,7 +388,7 @@ static void encode_band_info(AACEncContext *s, SingleChannelElement *sce)
 static void encode_scale_factors(AVCodecContext *avctx, AACEncContext *s,
                                  SingleChannelElement *sce)
 {
-    int diff, off_sf = sce->sf_idx[0], off_pns = sce->sf_idx[0];
+    int diff, off_sf = sce->sf_idx[0], off_pns = sce->sf_idx[0] - NOISE_OFFSET;
     int noise_flag = 1;
     int i, w;
 
-- 
2.1.4