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author | Kenan Gillet <kenan.gillet@gmail.com> | 2008-12-02 19:48:05 +0300 |
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committer | Vitor Sessak <vitor1001@gmail.com> | 2008-12-02 19:48:05 +0300 |
commit | 73b458e354d1daa73989b9ff0296235556cb55c3 (patch) | |
tree | 02d3659818a10c5580a25dea4eba38b35430a9ab /libavcodec/qcelp_lsp.c | |
parent | 2ba0cdd527416c4ecffd67884b5e116b10bb51cb (diff) |
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
Diffstat (limited to 'libavcodec/qcelp_lsp.c')
-rw-r--r-- | libavcodec/qcelp_lsp.c | 100 |
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; + } +} |