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Copy bap from previous block when exponent strategy is EXP_REUSE. 

We can do this because exponents are the only bit allocation parameters which
change from block-to-block currently.
Approx. 57% faster in function bit_alloc().
Approx. 25% faster overall encoding.

Originally committed as revision 26040 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Justin Ruggles 2010-12-16 22:47:07 +00:00
parent 126a29b871
commit 795063db3b
1 changed files with 8 additions and 0 deletions
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8
libavcodec/ac3enc.c
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@ -1028,10 +1028,18 @@ static int bit_alloc(AC3EncodeContext *s,
mant_cnt[1] = mant_cnt[2] = 2;
mant_cnt[4] = 1;
for (ch = 0; ch < s->channels; ch++) {
/* Currently the only bit allocation parameters which vary across
blocks within a frame are the exponent values. We can take
advantage of that by reusing the bit allocation pointers
whenever we reuse exponents. */
if (block->exp_strategy[ch] == EXP_REUSE) {
memcpy(block->bap[ch], s->blocks[blk-1].bap[ch], AC3_MAX_COEFS);
} else {
ff_ac3_bit_alloc_calc_bap(block->mask[ch], block->psd[ch], 0,
s->nb_coefs[ch], snr_offset,
s->bit_alloc.floor, ff_ac3_bap_tab,
block->bap[ch]);
}
mantissa_bits += compute_mantissa_size(mant_cnt, block->bap[ch], s->nb_coefs[ch]);
}
mantissa_bits += compute_mantissa_size_final(mant_cnt);