Commit last ok'ed parts of QCELP decoder and enable it.

patch by Kenan Gillet, kenan.gillet gmail com

Originally committed as revision 15978 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 100 insertions, 0 deletions

diff --git a/libavcodec/qcelp_lsp.c b/libavcodec/qcelp_lsp.c
new file mode 100644
index 0000000000..a4be00487c
--- /dev/null
+++ b/libavcodec/qcelp_lsp.c
@@ -0,0 +1,100 @@
+/*
+ * QCELP decoder
+ * Copyright (c) 2007 Reynaldo H. Verdejo Pinochet
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file qcelp_lsp.c
+ * QCELP decoder
+ * @author Reynaldo H. Verdejo Pinochet
+ */
+
+#include "libavutil/mathematics.h"
+
+/**
+ * initial coefficient to perform bandwidth expansion on LPC
+ *
+ * @note: 0.9883 looks like an approximation of 253/256.
+ *
+ * TIA/EIA/IS-733 2.4.3.3.6 6
+ */
+#define QCELP_BANDWITH_EXPANSION_COEFF 0.9883
+
+/**
+ * Computes the Pa / (1 + z(-1)) or Qa / (1 - z(-1)) coefficients
+ * needed for LSP to LPC conversion.
+ * We only need to calculate the 6 first elements of the polynomial.
+ *
+ * @param lspf line spectral pair frequencies
+ * @param f [out] polynomial input/output as a vector
+ *
+ * TIA/EIA/IS-733 2.4.3.3.5-1/2
+ */
+static void lsp2polyf(const float *lspf, double *f, int lp_half_order)
+{
+    int i, j;
+
+    f[0] = 1.0;
+    f[1] = -2 * cos(M_PI * lspf[0]);
+    lspf -= 2;
+    for(i=2; i<=lp_half_order; i++)
+    {
+        double val = -2 * cos(M_PI * lspf[2*i]);
+        f[i] = val * f[i-1] + 2*f[i-2];
+        for(j=i-1; j>1; j--)
+            f[j] += f[j-1] * val + f[j-2];
+        f[1] += val;
+    }
+}
+
+/**
+ * Reconstructs LPC coefficients from the line spectral pair frequencies
+ * and performs bandwidth expansion.
+ *
+ * @param lspf line spectral pair frequencies
+ * @param lpc linear predictive coding coefficients
+ *
+ * @note: bandwith_expansion_coeff could be precalculated into a table
+ *        but it seems to be slower on x86
+ *
+ * TIA/EIA/IS-733 2.4.3.3.5
+ */
+void ff_qcelp_lspf2lpc(const float *lspf, float *lpc)
+{
+    double pa[6], qa[6];
+    int   i;
+    double bandwith_expansion_coeff = -QCELP_BANDWITH_EXPANSION_COEFF * 0.5;
+
+    lsp2polyf(lspf,     pa, 5);
+    lsp2polyf(lspf + 1, qa, 5);
+
+    for (i=4; i>=0; i--)
+    {
+        double paf = pa[i+1] + pa[i];
+        double qaf = qa[i+1] - qa[i];
+
+        lpc[i  ] = paf + qaf;
+        lpc[9-i] = paf - qaf;
+    }
+    for (i=0; i<10; i++)
+    {
+        lpc[i] *= bandwith_expansion_coeff;
+        bandwith_expansion_coeff *= QCELP_BANDWITH_EXPANSION_COEFF;
+    }
+}