Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

275 lines (234 sloc) 8.011 kb
/*
* LPC utility code
* Copyright (c) 2006 Justin Ruggles <justin.ruggles@gmail.com>
*
* 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
*/
#include "libavutil/common.h"
#include "libavutil/lls.h"
#define LPC_USE_DOUBLE
#include "lpc.h"
#include "libavutil/avassert.h"
/**
* Apply Welch window function to audio block
*/
static void lpc_apply_welch_window_c(const int32_t *data, int len,
double *w_data)
{
int i, n2;
double w;
double c;
/* The optimization in commit fa4ed8c does not support odd len.
* If someone wants odd len extend that change. */
av_assert2(!(len & 1));
n2 = (len >> 1);
c = 2.0 / (len - 1.0);
w_data+=n2;
data+=n2;
for(i=0; i<n2; i++) {
w = c - n2 + i;
w = 1.0 - (w * w);
w_data[-i-1] = data[-i-1] * w;
w_data[+i ] = data[+i ] * w;
}
}
/**
* Calculate autocorrelation data from audio samples
* A Welch window function is applied before calculation.
*/
static void lpc_compute_autocorr_c(const double *data, int len, int lag,
double *autoc)
{
int i, j;
for(j=0; j<lag; j+=2){
double sum0 = 1.0, sum1 = 1.0;
for(i=j; i<len; i++){
sum0 += data[i] * data[i-j];
sum1 += data[i] * data[i-j-1];
}
autoc[j ] = sum0;
autoc[j+1] = sum1;
}
if(j==lag){
double sum = 1.0;
for(i=j-1; i<len; i+=2){
sum += data[i ] * data[i-j ]
+ data[i+1] * data[i-j+1];
}
autoc[j] = sum;
}
}
/**
* Quantize LPC coefficients
*/
static void quantize_lpc_coefs(double *lpc_in, int order, int precision,
int32_t *lpc_out, int *shift, int max_shift, int zero_shift)
{
int i;
double cmax, error;
int32_t qmax;
int sh;
/* define maximum levels */
qmax = (1 << (precision - 1)) - 1;
/* find maximum coefficient value */
cmax = 0.0;
for(i=0; i<order; i++) {
cmax= FFMAX(cmax, fabs(lpc_in[i]));
}
/* if maximum value quantizes to zero, return all zeros */
if(cmax * (1 << max_shift) < 1.0) {
*shift = zero_shift;
memset(lpc_out, 0, sizeof(int32_t) * order);
return;
}
/* calculate level shift which scales max coeff to available bits */
sh = max_shift;
while((cmax * (1 << sh) > qmax) && (sh > 0)) {
sh--;
}
/* since negative shift values are unsupported in decoder, scale down
coefficients instead */
if(sh == 0 && cmax > qmax) {
double scale = ((double)qmax) / cmax;
for(i=0; i<order; i++) {
lpc_in[i] *= scale;
}
}
/* output quantized coefficients and level shift */
error=0;
for(i=0; i<order; i++) {
error -= lpc_in[i] * (1 << sh);
lpc_out[i] = av_clip(lrintf(error), -qmax, qmax);
error -= lpc_out[i];
}
*shift = sh;
}
static int estimate_best_order(double *ref, int min_order, int max_order)
{
int i, est;
est = min_order;
for(i=max_order-1; i>=min_order-1; i--) {
if(ref[i] > 0.10) {
est = i+1;
break;
}
}
return est;
}
/**
* Calculate LPC coefficients for multiple orders
*
* @param lpc_type LPC method for determining coefficients,
* see #FFLPCType for details
*/
int ff_lpc_calc_coefs(LPCContext *s,
const int32_t *samples, int blocksize, int min_order,
int max_order, int precision,
int32_t coefs[][MAX_LPC_ORDER], int *shift,
enum FFLPCType lpc_type, int lpc_passes,
int omethod, int max_shift, int zero_shift)
{
double autoc[MAX_LPC_ORDER+1];
double ref[MAX_LPC_ORDER];
double lpc[MAX_LPC_ORDER][MAX_LPC_ORDER];
int i, j, pass;
int opt_order;
av_assert2(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER &&
lpc_type > FF_LPC_TYPE_FIXED);
/* reinit LPC context if parameters have changed */
if (blocksize != s->blocksize || max_order != s->max_order ||
lpc_type != s->lpc_type) {
ff_lpc_end(s);
ff_lpc_init(s, blocksize, max_order, lpc_type);
}
if (lpc_type == FF_LPC_TYPE_LEVINSON) {
s->lpc_apply_welch_window(samples, blocksize, s->windowed_samples);
s->lpc_compute_autocorr(s->windowed_samples, blocksize, max_order, autoc);
compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1);
for(i=0; i<max_order; i++)
ref[i] = fabs(lpc[i][i]);
} else if (lpc_type == FF_LPC_TYPE_CHOLESKY) {
LLSModel m[2];
double var[MAX_LPC_ORDER+1], av_uninit(weight);
if(lpc_passes <= 0)
lpc_passes = 2;
for(pass=0; pass<lpc_passes; pass++){
av_init_lls(&m[pass&1], max_order);
weight=0;
for(i=max_order; i<blocksize; i++){
for(j=0; j<=max_order; j++)
var[j]= samples[i-j];
if(pass){
double eval, inv, rinv;
eval= av_evaluate_lls(&m[(pass-1)&1], var+1, max_order-1);
eval= (512>>pass) + fabs(eval - var[0]);
inv = 1/eval;
rinv = sqrt(inv);
for(j=0; j<=max_order; j++)
var[j] *= rinv;
weight += inv;
}else
weight++;
av_update_lls(&m[pass&1], var, 1.0);
}
av_solve_lls(&m[pass&1], 0.001, 0);
}
for(i=0; i<max_order; i++){
for(j=0; j<max_order; j++)
lpc[i][j]=-m[(pass-1)&1].coeff[i][j];
ref[i]= sqrt(m[(pass-1)&1].variance[i] / weight) * (blocksize - max_order) / 4000;
}
for(i=max_order-1; i>0; i--)
ref[i] = ref[i-1] - ref[i];
}
opt_order = max_order;
if(omethod == ORDER_METHOD_EST) {
opt_order = estimate_best_order(ref, min_order, max_order);
i = opt_order-1;
quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
} else {
for(i=min_order-1; i<max_order; i++) {
quantize_lpc_coefs(lpc[i], i+1, precision, coefs[i], &shift[i], max_shift, zero_shift);
}
}
return opt_order;
}
av_cold int ff_lpc_init(LPCContext *s, int blocksize, int max_order,
enum FFLPCType lpc_type)
{
s->blocksize = blocksize;
s->max_order = max_order;
s->lpc_type = lpc_type;
if (lpc_type == FF_LPC_TYPE_LEVINSON) {
s->windowed_buffer = av_mallocz((blocksize + 2 + FFALIGN(max_order, 4)) *
sizeof(*s->windowed_samples));
if (!s->windowed_buffer)
return AVERROR(ENOMEM);
s->windowed_samples = s->windowed_buffer + FFALIGN(max_order, 4);
} else {
s->windowed_samples = NULL;
}
s->lpc_apply_welch_window = lpc_apply_welch_window_c;
s->lpc_compute_autocorr = lpc_compute_autocorr_c;
if (HAVE_MMX)
ff_lpc_init_x86(s);
return 0;
}
av_cold void ff_lpc_end(LPCContext *s)
{
av_freep(&s->windowed_buffer);
}
Jump to Line
Something went wrong with that request. Please try again.