aac: add additional fields needed by the encoder for intensity stereo

This commit adds additional fields which are used by the native encoder to add intensity stereo support. It also adds some clarifying statements to the comments for the codebooks.

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

libavcodec/aac.h

@@ -76,9 +76,10 @@ enum BandType {
     ZERO_BT        = 0,     ///< Scalefactors and spectral data are all zero.
     FIRST_PAIR_BT  = 5,     ///< This and later band types encode two values (rather than four) with one code word.
     ESC_BT         = 11,    ///< Spectral data are coded with an escape sequence.
+    RESERVED_BT    = 12,    ///< Band types following are encoded differently from others.
     NOISE_BT       = 13,    ///< Spectral data are scaled white noise not coded in the bitstream.
-    INTENSITY_BT2  = 14,    ///< Scalefactor data are intensity stereo positions.
-    INTENSITY_BT   = 15,    ///< Scalefactor data are intensity stereo positions.
+    INTENSITY_BT2  = 14,    ///< Scalefactor data are intensity stereo positions (out of phase).
+    INTENSITY_BT   = 15,    ///< Scalefactor data are intensity stereo positions (in phase).
 };
 
 #define IS_CODEBOOK_UNSIGNED(x) (((x) - 1) & 10)
@@ -237,6 +238,8 @@ typedef struct SingleChannelElement {
     float sf[120];                                  ///< scalefactors
     int sf_idx[128];                                ///< scalefactor indices (used by encoder)
     uint8_t zeroes[128];                            ///< band is not coded (used by encoder)
+    float  is_ener[128];                            ///< Intensity stereo pos (used by encoder)
+    float pns_ener[128];                            ///< Noise energy values (used by encoder)
     DECLARE_ALIGNED(32, float,   pcoeffs)[1024];    ///< coefficients for IMDCT, pristine
     DECLARE_ALIGNED(32, float,   coeffs)[1024];     ///< coefficients for IMDCT, maybe processed
     DECLARE_ALIGNED(32, float,   saved)[1536];      ///< overlap
@@ -254,7 +257,9 @@ typedef struct ChannelElement {
     // CPE specific
     int common_window;        ///< Set if channels share a common 'IndividualChannelStream' in bitstream.
     int     ms_mode;          ///< Signals mid/side stereo flags coding mode (used by encoder)
+    uint8_t is_mode;          ///< Set if any bands have been encoded using intensity stereo (used by encoder)
     uint8_t ms_mask[128];     ///< Set if mid/side stereo is used for each scalefactor window band
+    uint8_t is_mask[128];     ///< Set if intensity stereo is used (used by encoder)
     // shared
     SingleChannelElement ch[2];
     // CCE specific