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Reverse the exponent & exponent strategy array arrangement to simplify the 

per-channel exponent strategy decision.  This will also make it easier to
plug-in other exponent strategy algorithms.

Originally committed as revision 25995 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2010-12-14 14:53:17 +00:00
parent 67d979fede
commit d7da80806c
1 changed files with 29 additions and 16 deletions
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45
libavcodec/ac3enc.c
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@ -485,38 +485,34 @@ static int calc_exp_diff(uint8_t *exp1, uint8_t *exp2, int n)
/**
* Calculate exponent strategies for all blocks in a single channel.
*/
static void compute_exp_strategy_ch(uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS],
int ch, int is_lfe)
static void compute_exp_strategy_ch(uint8_t *exp_strategy, uint8_t **exp)
{
int blk, blk1;
int exp_diff;
/* estimate if the exponent variation & decide if they should be
reused in the next frame */
exp_strategy[0][ch] = EXP_NEW;
exp_strategy[0] = EXP_NEW;
for (blk = 1; blk < AC3_MAX_BLOCKS; blk++) {
exp_diff = calc_exp_diff(exp[blk][ch], exp[blk-1][ch], AC3_MAX_COEFS);
exp_diff = calc_exp_diff(exp[blk], exp[blk-1], AC3_MAX_COEFS);
if (exp_diff > EXP_DIFF_THRESHOLD)
exp_strategy[blk][ch] = EXP_NEW;
exp_strategy[blk] = EXP_NEW;
else
exp_strategy[blk][ch] = EXP_REUSE;
exp_strategy[blk] = EXP_REUSE;
}
if (is_lfe)
return;
/* now select the encoding strategy type : if exponents are often
recoded, we use a coarse encoding */
blk = 0;
while (blk < AC3_MAX_BLOCKS) {
blk1 = blk + 1;
while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1][ch] == EXP_REUSE)
while (blk1 < AC3_MAX_BLOCKS && exp_strategy[blk1] == EXP_REUSE)
blk1++;
switch (blk1 - blk) {
case 1: exp_strategy[blk][ch] = EXP_D45; break;
case 1: exp_strategy[blk] = EXP_D45; break;
case 2:
case 3: exp_strategy[blk][ch] = EXP_D25; break;
default: exp_strategy[blk][ch] = EXP_D15; break;
case 3: exp_strategy[blk] = EXP_D25; break;
default: exp_strategy[blk] = EXP_D15; break;
}
blk = blk1;
}
@ -525,15 +521,32 @@ static void compute_exp_strategy_ch(uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX
/**
* Calculate exponent strategies for all channels.
* Array arrangement is reversed to simplify the per-channel calculation.
*/
static void compute_exp_strategy(AC3EncodeContext *s,
uint8_t exp_strategy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS],
uint8_t exp[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][AC3_MAX_COEFS])
{
int ch;
uint8_t *exp1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
uint8_t exp_str1[AC3_MAX_CHANNELS][AC3_MAX_BLOCKS];
int ch, blk;
for (ch = 0; ch < s->channels; ch++) {
compute_exp_strategy_ch(exp_strategy, exp, ch, ch == s->lfe_channel);
for (ch = 0; ch < s->fbw_channels; ch++) {
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++) {
exp1[ch][blk] = exp[blk][ch];
exp_str1[ch][blk] = exp_strategy[blk][ch];
}
compute_exp_strategy_ch(exp_str1[ch], exp1[ch]);
for (blk = 0; blk < AC3_MAX_BLOCKS; blk++)
exp_strategy[blk][ch] = exp_str1[ch][blk];
}
if (s->lfe_on) {
ch = s->lfe_channel;
exp_strategy[0][ch] = EXP_D15;
for (blk = 1; blk < 5; blk++)
exp_strategy[blk][ch] = EXP_REUSE;
}
}