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Code Issues Releases Activity

atrac3: simplify MDCT window calculation

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This commit is contained in:
Justin Ruggles 2012-10-18 23:11:20 -04:00
parent 5d1007f74d
commit 327747de15
1 changed files with 7 additions and 10 deletions
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17
libavcodec/atrac3.c
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@ -177,19 +177,16 @@ static int decode_bytes(const uint8_t *input, uint8_t *out, int bytes)
static av_cold void init_atrac3_window(void)
{
float enc_window[256];
int i;
int i, j;
/* generate the mdct window, for details see
* http://wiki.multimedia.cx/index.php?title=RealAudio_atrc#Windows */
for (i = 0; i < 256; i++)
enc_window[i] = (sin(((i + 0.5) / 256.0 - 0.5) * M_PI) + 1.0) * 0.5;
for (i = 0; i < 256; i++) {
mdct_window[i] = enc_window[i] /
(enc_window[ i] * enc_window[ i] +
enc_window[255 - i] * enc_window[255 - i]);
mdct_window[511 - i] = mdct_window[i];
for (i = 0, j = 255; i < 128; i++, j--) {
float wi = sin(((i + 0.5) / 256.0 - 0.5) * M_PI) + 1.0;
float wj = sin(((j + 0.5) / 256.0 - 0.5) * M_PI) + 1.0;
float w = 0.5 * (wi * wi + wj * wj);
mdct_window[i] = mdct_window[511 - i] = wi / w;
mdct_window[j] = mdct_window[511 - j] = wj / w;
}
}