Add spectral extension to the E-AC-3 decoder.

Original patch by Justin, updated and resubmitted by
Christophe Gisquet, christophe D gisquet A gmail

Originally committed as revision 22734 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 47 insertions, 0 deletions

diff --git a/libavcodec/ac3dec.h b/libavcodec/ac3dec.h
index 78869b5e26..bd555bdde1 100644
--- a/libavcodec/ac3dec.h
+++ b/libavcodec/ac3dec.h
@@ -22,6 +22,29 @@
 /**
  * @file libavcodec/ac3.h
  * Common code between the AC-3 and E-AC-3 decoders.
+ *
+ * Summary of MDCT Coefficient Grouping:
+ * The individual MDCT coefficient indices are often referred to in the
+ * (E-)AC-3 specification as frequency bins.  These bins are grouped together
+ * into subbands of 12 coefficients each.  The subbands are grouped together
+ * into bands as defined in the bitstream by the band structures, which
+ * determine the number of bands and the size of each band.  The full spectrum
+ * of 256 frequency bins is divided into 1 DC bin + 21 subbands = 253 bins.
+ * This system of grouping coefficients is used for channel bandwidth, stereo
+ * rematrixing, channel coupling, enhanced coupling, and spectral extension.
+ *
+ * +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
+ * |1|  |12|  |  [12|12|12|12]  |  |  |  |  |  |  |  |  |  |  |  |  |3|
+ * +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
+ * ~~~  ~~~~     ~~~~~~~~~~~~~                                      ~~~
+ *  |     |            |                                             |
+ *  |     |            |                    3 unused frequency bins--+
+ *  |     |            |
+ *  |     |            +--1 band containing 4 subbands
+ *  |     |
+ *  |     +--1 subband of 12 frequency bins
+ *  |
+ *  +--DC frequency bin
  */
 
 #ifndef AVCODEC_AC3DEC_H
@@ -43,6 +66,7 @@
 #define AC3_MAX_COEFS   256
 #define AC3_BLOCK_SIZE  256
 #define MAX_BLOCKS        6
+#define SPX_MAX_BANDS    17
 
 typedef struct {
     AVCodecContext *avctx;                  ///< parent context
@@ -89,6 +113,22 @@ typedef struct {
     int cpl_coords[AC3_MAX_CHANNELS][18];   ///< coupling coordinates                   (cplco)
 ///@}
 
+///@defgroup spx spectral extension
+///@{
+    int spx_in_use;                             ///< spectral extension in use              (spxinu)
+    uint8_t channel_uses_spx[AC3_MAX_CHANNELS]; ///< channel uses spectral extension        (chinspx)
+    int8_t spx_atten_code[AC3_MAX_CHANNELS];    ///< spx attenuation code                   (spxattencod)
+    int spx_src_start_freq;                     ///< spx start frequency bin
+    int spx_dst_end_freq;                       ///< spx end frequency bin
+    int spx_dst_start_freq;                     ///< spx starting frequency bin for copying (copystartmant)
+                                                ///< the copy region ends at the start of the spx region.
+    int num_spx_bands;                          ///< number of spx bands                    (nspxbnds)
+    uint8_t spx_band_sizes[SPX_MAX_BANDS];      ///< number of bins in each spx band
+    uint8_t first_spx_coords[AC3_MAX_CHANNELS]; ///< first spx coordinates states           (firstspxcos)
+    float spx_noise_blend[AC3_MAX_CHANNELS][SPX_MAX_BANDS]; ///< spx noise blending factor  (nblendfact)
+    float spx_signal_blend[AC3_MAX_CHANNELS][SPX_MAX_BANDS];///< spx signal blending factor (sblendfact)
+///@}
+
 ///@defgroup aht adaptive hybrid transform
     int channel_uses_aht[AC3_MAX_CHANNELS];                         ///< channel AHT in use (chahtinu)
     int pre_mantissa[AC3_MAX_CHANNELS][AC3_MAX_COEFS][MAX_BLOCKS];  ///< pre-IDCT mantissas
@@ -182,4 +222,11 @@ void ff_eac3_decode_transform_coeffs_aht_ch(AC3DecodeContext *s, int ch);
 void ff_ac3_downmix_c(float (*samples)[256], float (*matrix)[2],
                       int out_ch, int in_ch, int len);
 
+/**
+ * Apply spectral extension to each channel by copying lower frequency
+ * coefficients to higher frequency bins and applying side information to
+ * approximate the original high frequency signal.
+ */
+void ff_eac3_apply_spectral_extension(AC3DecodeContext *s);
+
 #endif /* AVCODEC_AC3DEC_H */