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Revert "ac3enc: shift coefficients to 24-bit following MDCT rather than using an exponent offset."

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This reverts commit 7e0a284b9f.
revert at authors request due to better impementation

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Michael Niedermayer 2011-03-15 15:12:17 +01:00
parent f7a5e7791d
commit 27293b840c
3 changed files with 16 additions and 41 deletions
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13
libavcodec/ac3enc.c
View File

@ -78,7 +78,7 @@ typedef struct AC3Block {
int16_t **band_psd; ///< psd per critical band
int16_t **mask; ///< masking curve
uint16_t **qmant; ///< quantized mantissas
int8_t coeff_shift[AC3_MAX_CHANNELS]; ///< fixed-point coefficient shift values
int8_t exp_shift[AC3_MAX_CHANNELS]; ///< exponent shift values
uint8_t new_rematrixing_strategy; ///< send new rematrixing flags in this block
uint8_t rematrixing_flags[4]; ///< rematrixing flags
} AC3Block;
@ -269,7 +269,7 @@ static void apply_mdct(AC3EncodeContext *s)
apply_window(&s->dsp, s->windowed_samples, input_samples, s->mdct.window, AC3_WINDOW_SIZE);
block->coeff_shift[ch] = normalize_samples(s);
block->exp_shift[ch] = normalize_samples(s);
mdct512(&s->mdct, block->mdct_coef[ch], s->windowed_samples);
}
@ -416,13 +416,14 @@ static void extract_exponents(AC3EncodeContext *s)
AC3Block *block = &s->blocks[blk];
uint8_t *exp = block->exp[ch];
int32_t *coef = block->fixed_coef[ch];
int exp_shift = block->exp_shift[ch];
for (i = 0; i < AC3_MAX_COEFS; i++) {
int e;
int v = abs(coef[i]);
if (v == 0)
e = 24;
else {
e = 23 - av_log2(v);
e = 23 - av_log2(v) + exp_shift;
if (e >= 24) {
e = 24;
coef[i] = 0;
@ -1138,7 +1139,7 @@ static inline int asym_quant(int c, int e, int qbits)
* Quantize a set of mantissas for a single channel in a single block.
*/
static void quantize_mantissas_blk_ch(AC3EncodeContext *s, int32_t *fixed_coef,
uint8_t *exp,
int8_t exp_shift, uint8_t *exp,
uint8_t *bap, uint16_t *qmant, int n)
{
int i;
@ -1146,7 +1147,7 @@ static void quantize_mantissas_blk_ch(AC3EncodeContext *s, int32_t *fixed_coef,
for (i = 0; i < n; i++) {
int v;
int c = fixed_coef[i];
int e = exp[i];
int e = exp[i] - exp_shift;
int b = bap[i];
switch (b) {
case 0:
@ -1242,7 +1243,7 @@ static void quantize_mantissas(AC3EncodeContext *s)
s->qmant1_ptr = s->qmant2_ptr = s->qmant4_ptr = NULL;
for (ch = 0; ch < s->channels; ch++) {
quantize_mantissas_blk_ch(s, block->fixed_coef[ch],
quantize_mantissas_blk_ch(s, block->fixed_coef[ch], block->exp_shift[ch],
block->exp[ch], block->bap[ch],
block->qmant[ch], s->nb_coefs[ch]);
}

42
libavcodec/ac3enc_fixed.c
View File

@ -294,55 +294,29 @@ static void lshift_tab(int16_t *tab, int n, unsigned int lshift)
}
/**
* Shift each value in an array by a specified amount.
* @param src input array
* @param n number of values in the array
* @param shift shift amount (negative=right, positive=left)
*/
static void shift_int32(int32_t *src, int n, int shift)
{
int i;
if (shift > 0) {
for (i = 0; i < n; i++)
src[i] <<= shift;
} else if (shift < 0) {
shift = -shift;
for (i = 0; i < n; i++)
src[i] >>= shift;
}
}
/**
* Normalize the input samples to use the maximum available precision.
* This assumes signed 16-bit input samples.
* This assumes signed 16-bit input samples. Exponents are reduced by 9 to
* match the 24-bit internal precision for MDCT coefficients.
*
* @return coefficient shift
* @return exponent shift
*/
static int normalize_samples(AC3EncodeContext *s)
{
int v = 14 - log2_tab(s, s->windowed_samples, AC3_WINDOW_SIZE);
lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
return 9 - v;
return v - 9;
}
/**
* Scale MDCT coefficients to 24-bit fixed-point.
* Scale MDCT coefficients from float to fixed-point.
*/
static void scale_coefficients(AC3EncodeContext *s)
{
int blk, ch;
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
AC3Block *block = &s->blocks[blk];
for (ch = 0; ch < s->channels; ch++) {
shift_int32(block->mdct_coef[ch], AC3_MAX_COEFS,
block->coeff_shift[ch]);
}
}
/* scaling/conversion is obviously not needed for the fixed-point encoder
since the coefficients are already fixed-point. */
return;
}

2
tests/ref/acodec/ac3_fixed
View File

@ -1,2 +1,2 @@
5f1255da35a4ed00a2e932887c9aef77 *./tests/data/acodec/ac3.rm
07bd593823ebd721b3a32ef298bdfc20 *./tests/data/acodec/ac3.rm
98751 ./tests/data/acodec/ac3.rm