[FFmpeg-cvslog] Revert "ac3enc: shift coefficients to 24-bit following MDCT rather than using an exponent offset ."
Michael Niedermayer
git
Tue Mar 15 16:55:33 CET 2011
ffmpeg | branch: master | Michael Niedermayer <michaelni at gmx.at> | Tue Mar 15 15:12:17 2011 +0100| [27293b840ccae95ddb1f4d8af519e7962b0e373d] | committer: Michael Niedermayer
Revert "ac3enc: shift coefficients to 24-bit following MDCT rather than using an exponent offset."
This reverts commit 7e0a284b9f1967d46603711e85e0be01e084eadf.
revert at authors request due to better impementation
Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=27293b840ccae95ddb1f4d8af519e7962b0e373d
---
libavcodec/ac3enc.c | 13 +++++++------
libavcodec/ac3enc_fixed.c | 42 ++++++++----------------------------------
tests/ref/acodec/ac3_fixed | 2 +-
3 files changed, 16 insertions(+), 41 deletions(-)
diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c
index 863f200..baa9597 100644
--- a/libavcodec/ac3enc.c
+++ b/libavcodec/ac3enc.c
@@ -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]);
}
diff --git a/libavcodec/ac3enc_fixed.c b/libavcodec/ac3enc_fixed.c
index e5853a3..3de00ee 100644
--- a/libavcodec/ac3enc_fixed.c
+++ b/libavcodec/ac3enc_fixed.c
@@ -295,54 +295,28 @@ 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;
}
diff --git a/tests/ref/acodec/ac3_fixed b/tests/ref/acodec/ac3_fixed
index 89e0be5..f32443d 100644
--- a/tests/ref/acodec/ac3_fixed
+++ b/tests/ref/acodec/ac3_fixed
@@ -1,2 +1,2 @@
-5f1255da35a4ed00a2e932887c9aef77 *./tests/data/acodec/ac3.rm
+07bd593823ebd721b3a32ef298bdfc20 *./tests/data/acodec/ac3.rm
98751 ./tests/data/acodec/ac3.rm
More information about the ffmpeg-cvslog
mailing list