aacenc: Adjust the initial offset for PNS values

This commit adjusts the intial offset for PNS values, introduced
with commit f7f71b5795 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.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

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

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;