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Code Issues Releases Activity

Split applying of MDCT into several separate functions.

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Originally committed as revision 25990 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2010-12-14 14:52:59 +00:00
parent 4acc790f3c
commit 0a0a8500fb
1 changed files with 61 additions and 25 deletions
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86
libavcodec/ac3enc.c
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@ -312,6 +312,22 @@ static void mdct512(int32_t *out, int16_t *in)
}
/**
* Apply KBD window to input samples prior to MDCT.
*/
static void apply_window(int16_t *output, const int16_t *input,
const int16_t *window, int n)
{
int i;
int n2 = n >> 1;
for (i = 0; i < n2; i++) {
output[i] = MUL16(input[i], window[i]) >> 15;
output[n-i-1] = MUL16(input[n-i-1], window[i]) >> 15;
}
}
/**
* Calculate the log2() of the maximum absolute value in an array.
* @param tab input array
@ -351,6 +367,50 @@ static void lshift_tab(int16_t *tab, int n, int lshift)
}
/**
* Normalize the input samples to use the maximum available precision.
* This assumes signed 16-bit input samples. Exponents are reduced by 9 to
* match the 24-bit internal precision for MDCT coefficients.
*
* @return exponent shift
*/
static int normalize_samples(AC3EncodeContext *s,
int16_t windowed_samples[AC3_WINDOW_SIZE])
{
int v = 14 - log2_tab(windowed_samples, AC3_WINDOW_SIZE);
v = FFMAX(0, v);
lshift_tab(windowed_samples, AC3_WINDOW_SIZE, v);
return v - 9;
}
/**
* Apply the MDCT to input samples to generate frequency coefficients.
* This applies the KBD window and normalizes the input to reduce precision
* loss due to fixed-point calculations.
*/
static void apply_mdct(AC3EncodeContext *s,
int16_t planar_samples[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE+AC3_FRAME_SIZE],
int8_t exp_shift[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
int32_t mdct_coef[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS])
{
int blk, ch;
int16_t windowed_samples[AC3_WINDOW_SIZE];
for (ch = 0; ch < s->channels; ch++) {
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
const int16_t *input_samples = &planar_samples[ch][blk * AC3_BLOCK_SIZE];
apply_window(windowed_samples, input_samples, ff_ac3_window, AC3_WINDOW_SIZE);
exp_shift[blk][ch] = normalize_samples(s, windowed_samples);
mdct512(mdct_coef[blk][ch], windowed_samples);
}
}
}
/**
* Calculate the sum of absolute differences (SAD) between 2 sets of exponents.
*/
@ -1117,7 +1177,6 @@ static int ac3_encode_frame(AVCodecContext *avctx,
int v;
int blk, blk1, blk2, ch, i;
int16_t planar_samples[AC3_MAX_CHANNELS][AC3_BLOCK_SIZE+AC3_FRAME_SIZE];
int16_t windowed_samples[AC3_WINDOW_SIZE];
int32_t mdct_coef[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];
uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS];
uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS];
@ -1128,30 +1187,7 @@ static int ac3_encode_frame(AVCodecContext *avctx,
deinterleave_input_samples(s, samples, planar_samples);
/* apply MDCT */
for (ch = 0; ch < s->channels; ch++) {
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
int16_t *input_samples = &planar_samples[ch][blk * AC3_BLOCK_SIZE];
/* apply the MDCT window */
for (i = 0; i < AC3_BLOCK_SIZE; i++) {
windowed_samples[i] = MUL16(input_samples[i],
ff_ac3_window[i]) >> 15;
windowed_samples[AC3_WINDOW_SIZE-i-1] = MUL16(input_samples[AC3_WINDOW_SIZE-i-1],
ff_ac3_window[i]) >> 15;
}
/* Normalize the samples to use the maximum available precision */
v = 14 - log2_tab(windowed_samples, AC3_WINDOW_SIZE);
if (v < 0)
v = 0;
exp_shift[blk][ch] = v - 9;
lshift_tab(windowed_samples, AC3_WINDOW_SIZE, v);
/* do the MDCT */
mdct512(mdct_coef[blk][ch], windowed_samples);
}
}
apply_mdct(s, planar_samples, exp_shift, mdct_coef);
/* extract exponents */
for (ch = 0; ch < s->channels; ch++) {