[FFmpeg-soc] [soc]AMR-WB decoder branch, master, updated.

[Marcelo Póvoa]

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- Log -----------------------------------------------------------------
commit 1c399e4d298648f1ad8a70f50507c41fa7b21a62
Author: Marcelo Povoa <marspeoplester at gmail.com>
Date:   Thu Jul 29 02:51:15 2010 -0300

    Finish writing the ISF vector extrapolation (6k60 HB)
    Fix white noise excitation randomness

diff --git a/libavcodec/amrwbdata.h b/libavcodec/amrwbdata.h
index acfb443..ce5fb63 100644
--- a/libavcodec/amrwbdata.h
+++ b/libavcodec/amrwbdata.h
@@ -28,8 +28,7 @@
 #define LP_ORDER_16k          20               ///< lpc filter order at 16kHz
 #define UPS_FIR_SIZE          12               ///< upsampling filter size
 #define UPS_MEM_SIZE          2 * UPS_FIR_SIZE
-//#define SAMPLE_MEM            24               ///< number of stored past samples given by
-                                               ///< max(LP_ORDER, UPS_FIR_SIZE * 2)
+
 #define MIN_ISF_SPACING       (128 / 32768.0)  ///< minimum isf gap
 #define PRED_FACTOR           (1.0 / 3.0)
 #define MIN_ENERGY           -14.0             ///< initial innnovation energy (dB)
@@ -39,7 +38,6 @@
 #define AMRWB_SUBFRAME_SIZE   64               ///< samples per subframe at 12.8 kHz
 #define AMRWB_SFR_SIZE_OUT    80               ///< samples per subframe at 16 kHz
 #define AMRWB_SAMPLE_BOUND    32768.0          ///< threshold for synthesis overflow
-
 #define AMRWB_P_DELAY_MAX     231              ///< maximum pitch delay value
 #define AMRWB_P_DELAY_MIN     34
 
diff --git a/libavcodec/amrwbdec.c b/libavcodec/amrwbdec.c
index 83303ed..6833f23 100644
--- a/libavcodec/amrwbdec.c
+++ b/libavcodec/amrwbdec.c
@@ -1033,7 +1033,7 @@ static void scaled_hb_excitation(AMRWBContext *ctx, float *hb_exc,
 
     /* Generate a white-noise excitation */
     for (i = 0; i < AMRWB_SUBFRAME_SIZE; i++)
-        hb_exc[i] = 32768.0 - (uint16_t) av_lfg_get(&ctx->prng) / 65536.0;
+        hb_exc[i] = 32768.0 - (uint16_t) av_lfg_get(&ctx->prng);
 
     ff_scale_vector_to_given_sum_of_squares(hb_exc, hb_exc, energy,
                                             AMRWB_SUBFRAME_SIZE);
@@ -1042,6 +1042,9 @@ static void scaled_hb_excitation(AMRWBContext *ctx, float *hb_exc,
         hb_exc[i] *= hb_gain;
 }
 
+/**
+ * Calculate auto-correlation for the ISF difference vector
+ */
 static float auto_correlation(float *diff_isf, float mean, int lag)
 {
     int i;
@@ -1054,10 +1057,19 @@ static float auto_correlation(float *diff_isf, float mean, int lag)
     return sum;
 }
 
+/**
+ * Extrapolate a ISF vector to the 16kHz range (20th order LP)
+ * used at mode 6k60 LP filter for the high-freq band
+ *
+ * @param out                [out] buffer for extrapolated isf
+ * @param isf                [in] input isf vector
+ */
 static void extrapolate_isf(float *out, float *isf)
 {
     float diff_isf[LP_ORDER - 2], diff_mean;
+    float *diff_hi = diff_isf - LP_ORDER + 1; // diff array for extrapolated indices
     float corr_lag[3];
+    float est, scale;
     int i, i_max_corr;
 
     memcpy(out, isf, LP_ORDER - 1);
@@ -1083,7 +1095,32 @@ static void extrapolate_isf(float *out, float *isf)
     for (i = LP_ORDER - 1; i < LP_ORDER_16k - 1; i++)
         out[i] = isf[i - 1] + isf[i - 1 - i_max_corr]
                             - isf[i - 2 - i_max_corr];
-    return;
+
+    /* Calculate an estimate for ISF(18) and scale ISF based on the error */
+    est   = 79.65 + (out[2] - out[3] - out[4]) / 6.0;
+    scale = (FFMIN(est, 76.0) - out[LP_ORDER - 2]) /
+            (out[LP_ORDER_16k - 2] - out[LP_ORDER - 2]);
+    // XXX: should divide numerator by 2.0?
+
+    for (i = LP_ORDER - 1; i < LP_ORDER_16k - 1; i++)
+        diff_hi[i] = scale * (out[i] - out[i - 1]);
+
+    /* Stability insurance */
+    for (i = LP_ORDER; i < LP_ORDER_16k - 1; i++)
+        if (diff_hi[i] + diff_hi[i - 1] < 5.0) {
+            if (diff_hi[i] > diff_hi[i - 1]) {
+                diff_hi[i - 1] = 5.0 - diff_hi[i];
+            } else
+                diff_hi[i] = 5.0 - diff_hi[i - 1];
+        }
+
+    for (i = LP_ORDER - 1; i < LP_ORDER_16k - 1; i++)
+        out[i] = out[i - 1] + diff_hi[i];
+
+    /* XXX: Don't know why this 26214 coefficient, maybe it is not Q8 */
+    /* Scale the ISF vector for 16000 Hz */
+    for (i = 0; i < LP_ORDER_16k - 1; i++)
+        out[i] *= 26214 / (float) (1 << 8);
 }
 
 /**

-----------------------------------------------------------------------

Summary of changes:
 libavcodec/amrwbdata.h |    4 +---
 libavcodec/amrwbdec.c  |   41 +++++++++++++++++++++++++++++++++++++++--
 2 files changed, 40 insertions(+), 5 deletions(-)


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