mirror of
https://git.ffmpeg.org/ffmpeg.git
synced 2024-12-23 15:53:08 +00:00
87574416f7
more general' changeset. This one relocates the QCELP especific code to the qcelpdec.* files. Originally committed as revision 17800 to svn://svn.ffmpeg.org/ffmpeg/trunk
82 lines
2.2 KiB
C
82 lines
2.2 KiB
C
/*
|
|
* 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 libavcodec/qcelp_lsp.c
|
|
* QCELP decoder
|
|
* @author Reynaldo H. Verdejo Pinochet
|
|
* @remark FFmpeg merging spearheaded by Kenan Gillet
|
|
* @remark Development mentored by Benjamin Larson
|
|
*/
|
|
|
|
#include "libavutil/mathematics.h"
|
|
|
|
/**
|
|
* 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 double *lspf, double *f, int lp_half_order)
|
|
{
|
|
int i, j;
|
|
|
|
f[0] = 1.0;
|
|
f[1] = -2 * lspf[0];
|
|
lspf -= 2;
|
|
for(i=2; i<=lp_half_order; i++)
|
|
{
|
|
double val = -2 * 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.
|
|
*
|
|
* @param lspf line spectral pair frequencies
|
|
* @param lpc linear predictive coding coefficients
|
|
*/
|
|
void ff_celp_lspf2lpc(const double *lspf, float *lpc)
|
|
{
|
|
double pa[6], qa[6];
|
|
int i;
|
|
|
|
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 ] = 0.5*(paf+qaf);
|
|
lpc[9-i] = 0.5*(paf-qaf);
|
|
}
|
|
}
|