[FFmpeg-cvslog] ac3enc: do not right-shift fixed-point coefficients in the final MDCT stage .
Justin
git
Tue Mar 15 16:55:22 CET 2011
ffmpeg | branch: master | Justin <justin.ruggles at gmail.com> | Fri Mar 11 13:03:26 2011 -0500| [323e6fead07c75f418e4b60704a4f437bb3483b2] | committer: Justin Ruggles
ac3enc: do not right-shift fixed-point coefficients in the final MDCT stage.
This increases the accuracy of coefficients, leading to improved quality.
Rescaling of the coefficients to full 25-bit accuracy is done rather than
offsetting the exponent values. This requires coefficient scaling to be done
before determining the rematrixing strategy. Also, the rematrixing strategy
calculation must use 64-bit math to prevent overflow due to the higher
precision coefficients.
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=323e6fead07c75f418e4b60704a4f437bb3483b2
---
libavcodec/ac3enc.c | 25 ++++++++++-----------
libavcodec/ac3enc_fixed.c | 49 ++++++++++++++++++++++++++++++++-----------
libavcodec/ac3enc_fixed.h | 2 +
libavcodec/ac3enc_float.h | 2 +
tests/ref/acodec/ac3_fixed | 2 +-
tests/ref/lavf/rm | 2 +-
tests/ref/seek/ac3_rm | 22 +++++++++---------
7 files changed, 65 insertions(+), 39 deletions(-)
diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c
index baa9597..4c01fe3 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 exp_shift[AC3_MAX_CHANNELS]; ///< exponent shift values
+ uint8_t coeff_shift[AC3_MAX_CHANNELS]; ///< fixed-point coefficient 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->exp_shift[ch] = normalize_samples(s);
+ block->coeff_shift[ch] = normalize_samples(s);
mdct512(&s->mdct, block->mdct_coef[ch], s->windowed_samples);
}
@@ -328,10 +328,10 @@ static void compute_rematrixing_strategy(AC3EncodeContext *s)
CoefType rt = block->mdct_coef[1][i];
CoefType md = lt + rt;
CoefType sd = lt - rt;
- sum[0] += lt * lt;
- sum[1] += rt * rt;
- sum[2] += md * md;
- sum[3] += sd * sd;
+ MAC_COEF(sum[0], lt, lt);
+ MAC_COEF(sum[1], rt, rt);
+ MAC_COEF(sum[2], md, md);
+ MAC_COEF(sum[3], sd, sd);
}
/* compare sums to determine if rematrixing will be used for this band */
@@ -416,14 +416,13 @@ 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) + exp_shift;
+ e = 23 - av_log2(v);
if (e >= 24) {
e = 24;
coef[i] = 0;
@@ -1139,7 +1138,7 @@ 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,
- int8_t exp_shift, uint8_t *exp,
+ uint8_t *exp,
uint8_t *bap, uint16_t *qmant, int n)
{
int i;
@@ -1147,7 +1146,7 @@ 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] - exp_shift;
+ int e = exp[i];
int b = bap[i];
switch (b) {
case 0:
@@ -1243,7 +1242,7 @@ 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], block->exp_shift[ch],
+ quantize_mantissas_blk_ch(s, block->fixed_coef[ch],
block->exp[ch], block->bap[ch],
block->qmant[ch], s->nb_coefs[ch]);
}
@@ -1507,10 +1506,10 @@ static int ac3_encode_frame(AVCodecContext *avctx, unsigned char *frame,
apply_mdct(s);
- compute_rematrixing_strategy(s);
-
scale_coefficients(s);
+ compute_rematrixing_strategy(s);
+
apply_rematrixing(s);
process_exponents(s);
diff --git a/libavcodec/ac3enc_fixed.c b/libavcodec/ac3enc_fixed.c
index 3de00ee..e750a39 100644
--- a/libavcodec/ac3enc_fixed.c
+++ b/libavcodec/ac3enc_fixed.c
@@ -131,10 +131,10 @@ mdct_alloc_fail:
/** Complex multiply */
-#define CMUL(pre, pim, are, aim, bre, bim) \
+#define CMUL(pre, pim, are, aim, bre, bim, rshift) \
{ \
- pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15; \
- pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15; \
+ pre = (MUL16(are, bre) - MUL16(aim, bim)) >> rshift; \
+ pim = (MUL16(are, bim) + MUL16(bre, aim)) >> rshift; \
}
@@ -195,7 +195,7 @@ static void fft(AC3MDCTContext *mdct, IComplex *z, int ln)
p++;
q++;
for(l = nblocks; l < np2; l += nblocks) {
- CMUL(tmp_re, tmp_im, mdct->costab[l], -mdct->sintab[l], q->re, q->im);
+ CMUL(tmp_re, tmp_im, mdct->costab[l], -mdct->sintab[l], q->re, q->im, 15);
BF(p->re, p->im, q->re, q->im,
p->re, p->im, tmp_re, tmp_im);
p++;
@@ -234,7 +234,7 @@ static void mdct512(AC3MDCTContext *mdct, int32_t *out, int16_t *in)
for (i = 0; i < n4; i++) {
re = ((int)rot[ 2*i] - (int)rot[ n-1-2*i]) >> 1;
im = -((int)rot[n2+2*i] - (int)rot[n2-1-2*i]) >> 1;
- CMUL(x[i].re, x[i].im, re, im, -mdct->xcos1[i], mdct->xsin1[i]);
+ CMUL(x[i].re, x[i].im, re, im, -mdct->xcos1[i], mdct->xsin1[i], 15);
}
fft(mdct, x, mdct->nbits - 2);
@@ -243,7 +243,7 @@ static void mdct512(AC3MDCTContext *mdct, int32_t *out, int16_t *in)
for (i = 0; i < n4; i++) {
re = x[i].re;
im = x[i].im;
- CMUL(out[n2-1-2*i], out[2*i], re, im, mdct->xsin1[i], mdct->xcos1[i]);
+ CMUL(out[n2-1-2*i], out[2*i], re, im, mdct->xsin1[i], mdct->xcos1[i], 0);
}
}
@@ -295,9 +295,25 @@ static void lshift_tab(int16_t *tab, int n, unsigned int lshift)
/**
+ * Right-shift each value in an array of int32_t by a specified amount.
+ * @param src input array
+ * @param len number of values in the array
+ * @param shift right shift amount
+ */
+static void ac3_rshift_int32_c(int32_t *src, unsigned int len, unsigned int shift)
+{
+ int i;
+
+ if (shift > 0) {
+ for (i = 0; i < len; i++)
+ src[i] >>= shift;
+ }
+}
+
+
+/**
* 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.
+ * This assumes signed 16-bit input samples.
*
* @return exponent shift
*/
@@ -305,18 +321,25 @@ 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 v - 9;
+ /* +6 to right-shift from 31-bit to 25-bit */
+ return v + 6;
}
/**
- * Scale MDCT coefficients from float to fixed-point.
+ * Scale MDCT coefficients to 25-bit signed fixed-point.
*/
static void scale_coefficients(AC3EncodeContext *s)
{
- /* scaling/conversion is obviously not needed for the fixed-point encoder
- since the coefficients are already fixed-point. */
- return;
+ int blk, ch;
+
+ for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
+ AC3Block *block = &s->blocks[blk];
+ for (ch = 0; ch < s->channels; ch++) {
+ ac3_rshift_int32_c(block->mdct_coef[ch], AC3_MAX_COEFS,
+ block->coeff_shift[ch]);
+ }
+ }
}
diff --git a/libavcodec/ac3enc_fixed.h b/libavcodec/ac3enc_fixed.h
index 12c8ace..bad2306 100644
--- a/libavcodec/ac3enc_fixed.h
+++ b/libavcodec/ac3enc_fixed.h
@@ -36,6 +36,8 @@ typedef int16_t SampleType;
typedef int32_t CoefType;
typedef int64_t CoefSumType;
+#define MAC_COEF(d,a,b) MAC64(d,a,b)
+
/**
* Compex number.
diff --git a/libavcodec/ac3enc_float.h b/libavcodec/ac3enc_float.h
index 1726ca0..a4702bb 100644
--- a/libavcodec/ac3enc_float.h
+++ b/libavcodec/ac3enc_float.h
@@ -36,6 +36,8 @@ typedef float SampleType;
typedef float CoefType;
typedef float CoefSumType;
+#define MAC_COEF(d,a,b) ((d)+=(a)*(b))
+
typedef struct AC3MDCTContext {
const float *window; ///< MDCT window function
diff --git a/tests/ref/acodec/ac3_fixed b/tests/ref/acodec/ac3_fixed
index f32443d..4ef69ff 100644
--- a/tests/ref/acodec/ac3_fixed
+++ b/tests/ref/acodec/ac3_fixed
@@ -1,2 +1,2 @@
-07bd593823ebd721b3a32ef298bdfc20 *./tests/data/acodec/ac3.rm
+b3a8f0a8809a58b2ece90744f06fff96 *./tests/data/acodec/ac3.rm
98751 ./tests/data/acodec/ac3.rm
diff --git a/tests/ref/lavf/rm b/tests/ref/lavf/rm
index b8bf220..53b1255 100644
--- a/tests/ref/lavf/rm
+++ b/tests/ref/lavf/rm
@@ -1,2 +1,2 @@
-d149fc272dfd21fb8908ee21d7b1651b *./tests/data/lavf/lavf.rm
+7da378131db880bcf2e58305d54418ec *./tests/data/lavf/lavf.rm
346706 ./tests/data/lavf/lavf.rm
diff --git a/tests/ref/seek/ac3_rm b/tests/ref/seek/ac3_rm
index 07fcfa1..9b7db9a 100644
--- a/tests/ref/seek/ac3_rm
+++ b/tests/ref/seek/ac3_rm
@@ -4,28 +4,29 @@ ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
ret: 0 st:-1 flags:1 ts: 1.894167
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
ret: 0 st: 0 flags:0 ts: 0.788000
-ret: 0 st: 0 flags:1 dts:4160806.587000 pts:4160806.587000 pos: 3883 size: 116
+ret: 0 st: 0 flags:1 dts:12581.487000 pts:12581.487000 pos: 5822 size: 916
ret: 0 st: 0 flags:1 ts:-0.317000
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
ret: 0 st:-1 flags:0 ts: 2.576668
-ret: 0 st: 0 flags:1 dts:4160806.587000 pts:4160806.587000 pos: 3883 size: 116
+ret: 0 st: 0 flags:1 dts:524.800000 pts:524.800000 pos: 6155 size: 244
ret:-1 st:-1 flags:1 ts: 1.470835
ret: 0 st: 0 flags:0 ts: 0.365000
-ret: 0 st: 0 flags:1 dts:4160806.587000 pts:4160806.587000 pos: 3883 size: 116
+ret: 0 st: 0 flags:1 dts:12581.487000 pts:12581.487000 pos: 5822 size: 916
ret: 0 st: 0 flags:1 ts:-0.741000
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
ret:-1 st:-1 flags:0 ts: 2.153336
-ret:-1 st:-1 flags:1 ts: 1.047503
+ret: 0 st:-1 flags:1 ts: 1.047503
+ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
ret: 0 st: 0 flags:0 ts:-0.058000
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
-ret:-1 st: 0 flags:1 ts: 2.836000
+ret: 0 st: 0 flags:1 ts: 2.836000
+ret: 0 st: 0 flags:1 dts: 2.681000 pts: 2.681000 pos: 44105 size: 558
ret:-1 st:-1 flags:0 ts: 1.730004
ret: 0 st:-1 flags:1 ts: 0.624171
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
ret: 0 st: 0 flags:0 ts:-0.482000
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
-ret: 0 st: 0 flags:1 ts: 2.413000
-ret: 0 st: 0 flags:1 dts: 2.229000 pts: 2.229000 pos: 36705 size: 556
+ret:-1 st: 0 flags:1 ts: 2.413000
ret:-1 st:-1 flags:0 ts: 1.306672
ret: 0 st:-1 flags:1 ts: 0.200839
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
@@ -33,13 +34,12 @@ ret: 0 st: 0 flags:0 ts:-0.905000
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
ret:-1 st: 0 flags:1 ts: 1.989000
ret: 0 st:-1 flags:0 ts: 0.883340
-ret: 0 st: 0 flags:1 dts:4160806.587000 pts:4160806.587000 pos: 3883 size: 116
+ret: 0 st: 0 flags:1 dts:12581.487000 pts:12581.487000 pos: 5822 size: 916
ret: 0 st:-1 flags:1 ts:-0.222493
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
-ret: 0 st: 0 flags:0 ts: 2.672000
-ret: 0 st: 0 flags:1 dts:6354.691000 pts:6354.691000 pos: 10783 size: 304
+ret:-1 st: 0 flags:0 ts: 2.672000
ret:-1 st: 0 flags:1 ts: 1.566000
ret: 0 st:-1 flags:0 ts: 0.460008
-ret: 0 st: 0 flags:1 dts:4160806.587000 pts:4160806.587000 pos: 3883 size: 116
+ret: 0 st: 0 flags:1 dts:12581.487000 pts:12581.487000 pos: 5822 size: 916
ret: 0 st:-1 flags:1 ts:-0.645825
ret: 0 st: 0 flags:1 dts: 0.000000 pts: 0.000000 pos: 271 size: 556
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