aacdec: Implement LTP support.

Ported from gsoc svn.
(cherry picked from commit ead15f1d)

libavcodec/aac.h

@@ -43,6 +43,7 @@
 #define MAX_ELEM_ID 16
 
 #define TNS_MAX_ORDER 20
+#define MAX_LTP_LONG_SFB 40
 
 enum RawDataBlockType {
     TYPE_SCE,
@@ -130,6 +131,16 @@ typedef struct {
 #define SCALE_MAX_DIFF   60    ///< maximum scalefactor difference allowed by standard
 #define SCALE_DIFF_ZERO  60    ///< codebook index corresponding to zero scalefactor indices difference
 
+/**
+ * Long Term Prediction
+ */
+typedef struct {
+    int8_t present;
+    int16_t lag;
+    float coef;
+    int8_t used[MAX_LTP_LONG_SFB];
+} LongTermPrediction;
+
 /**
  * Individual Channel Stream
  */
@@ -139,6 +150,7 @@ typedef struct {
     uint8_t use_kb_window[2];   ///< If set, use Kaiser-Bessel window, otherwise use a sinus window.
     int num_window_groups;
     uint8_t group_len[8];
+    LongTermPrediction ltp;
     const uint16_t *swb_offset; ///< table of offsets to the lowest spectral coefficient of a scalefactor band, sfb, for a particular window
     const uint8_t *swb_sizes;   ///< table of scalefactor band sizes for a particular window
     int num_swb;                ///< number of scalefactor window bands
@@ -206,14 +218,15 @@ typedef struct {
     IndividualChannelStream ics;
     TemporalNoiseShaping tns;
     Pulse pulse;
-    enum BandType band_type[128];             ///< band types
-    int band_type_run_end[120];               ///< band type run end points
-    float sf[120];                            ///< scalefactors
-    int sf_idx[128];                          ///< scalefactor indices (used by encoder)
-    uint8_t zeroes[128];                      ///< band is not coded (used by encoder)
-    DECLARE_ALIGNED(16, float, coeffs)[1024]; ///< coefficients for IMDCT
-    DECLARE_ALIGNED(16, float, saved)[1024];  ///< overlap
-    DECLARE_ALIGNED(16, float, ret)[2048];    ///< PCM output
+    enum BandType band_type[128];                   ///< band types
+    int band_type_run_end[120];                     ///< band type run end points
+    float sf[120];                                  ///< scalefactors
+    int sf_idx[128];                                ///< scalefactor indices (used by encoder)
+    uint8_t zeroes[128];                            ///< band is not coded (used by encoder)
+    DECLARE_ALIGNED(16, float,   coeffs)[1024];     ///< coefficients for IMDCT
+    DECLARE_ALIGNED(16, float,   saved)[1024];      ///< overlap
+    DECLARE_ALIGNED(16, float,   ret)[2048];        ///< PCM output
+    DECLARE_ALIGNED(16, int16_t, ltp_state)[3072];  ///< time signal for LTP
     PredictorState predictor_state[MAX_PREDICTORS];
 } SingleChannelElement;
 
@@ -259,7 +272,7 @@ typedef struct {
      * @defgroup temporary aligned temporary buffers (We do not want to have these on the stack.)
      * @{
      */
-    DECLARE_ALIGNED(16, float, buf_mdct)[1024];
+    DECLARE_ALIGNED(16, float, buf_mdct)[2048];
     /** @} */
 
     /**
@@ -268,6 +281,7 @@ typedef struct {
      */
     FFTContext mdct;
     FFTContext mdct_small;
+    FFTContext mdct_ltp;
     DSPContext dsp;
     FmtConvertContext fmt_conv;
     int random_state;

libavcodec/aacdectab.h

@@ -35,6 +35,14 @@
 
 #include <stdint.h>
 
+/* @name ltp_coef
+ * Table of the LTP coefficient (multiplied by 2)
+ */
+static const float ltp_coef[8] = {
+     1.141658,    1.393232,    1.626008,    1.822608,
+     1.969800,    2.135788,    2.2389202,   2.739066,
+};
+
 /* @name tns_tmp2_map
  * Tables of the tmp2[] arrays of LPC coefficients used for TNS.
  * The suffix _M_N[] indicate the values of coef_compress and coef_res

libavcodec/mpeg4audio.h

@@ -57,7 +57,7 @@ enum AudioObjectType {
     AOT_AAC_MAIN,              ///< Y                       Main
     AOT_AAC_LC,                ///< Y                       Low Complexity
     AOT_AAC_SSR,               ///< N (code in SoC repo)    Scalable Sample Rate
-    AOT_AAC_LTP,               ///< N (code in SoC repo)    Long Term Prediction
+    AOT_AAC_LTP,               ///< Y                       Long Term Prediction
     AOT_SBR,                   ///< Y                       Spectral Band Replication
     AOT_AAC_SCALABLE,          ///< N                       Scalable
     AOT_TWINVQ,                ///< N                       Twin Vector Quantizer