diff options
Diffstat (limited to 'libavcodec/lpc.c')
| -rw-r--r-- | libavcodec/lpc.c | 64 |
1 files changed, 63 insertions, 1 deletions
diff --git a/libavcodec/lpc.c b/libavcodec/lpc.c index 896db51759..49e41d8c34 100644 --- a/libavcodec/lpc.c +++ b/libavcodec/lpc.c @@ -27,6 +27,68 @@ /** + * Apply Welch window function to audio block + */ +static void apply_welch_window(const int32_t *data, int len, double *w_data) +{ + int i, n2; + double w; + double c; + + assert(!(len&1)); //the optimization in r11881 does not support odd len + //if someone wants odd len extend the change in r11881 + + 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; + } +} + +/** + * Calculates autocorrelation data from audio samples + * A Welch window function is applied before calculation. + */ +void ff_lpc_compute_autocorr(const int32_t *data, int len, int lag, + double *autoc) +{ + int i, j; + double tmp[len + lag + 1]; + double *data1= tmp + lag; + + apply_welch_window(data, len, data1); + + for(j=0; j<lag; j++) + data1[j-lag]= 0.0; + data1[len] = 0.0; + + for(j=0; j<lag; j+=2){ + double sum0 = 1.0, sum1 = 1.0; + for(i=j; i<len; i++){ + sum0 += data1[i] * data1[i-j]; + sum1 += data1[i] * data1[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 += data1[i ] * data1[i-j ] + + data1[i+1] * data1[i-j+1]; + } + autoc[j] = sum; + } +} + +/** * Quantize LPC coefficients */ static void quantize_lpc_coefs(double *lpc_in, int order, int precision, @@ -115,7 +177,7 @@ int ff_lpc_calc_coefs(DSPContext *s, assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER && use_lpc > 0); if(use_lpc == 1){ - s->flac_compute_autocorr(samples, blocksize, max_order, autoc); + s->lpc_compute_autocorr(samples, blocksize, max_order, autoc); compute_lpc_coefs(autoc, max_order, &lpc[0][0], MAX_LPC_ORDER, 0, 1); |