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Make collapse-detection bitexact.

Browse source 
Jean-Marc's original anti-collapse patch used a threshold on the
 content of a decoded band to determine whether or not it should
 be filled with random noise.
Since this is highly sensitive to the accuracy of the
 implementation, it could lead to significant decoder output
 differences even if decoding error up to that point was relatively
 small.

This patch detects collapsed bands from the output of the vector
 quantizer, using exact integer arithmetic.
It makes two simplifying assumptions:
 a) If either input to haar1() is non-zero during TF resolution
     adjustments, then the output will be non-zero.
 b) If the content of a block is non-zero in any of the bands that
     are used for folding, then the folded output will be non-zero.
b) in particular is likely to be false when SPREAD_NONE is used.
It also ignores the case where mid and side are orthogonal in
 stereo_merge, but this is relatively unlikely.
This misses just over 3% of the cases that Jean-Marc's anti-collapse
 detection strategy would catch, but does not mis-classify any (all
 detected collapses are true collapses).

This patch overloads the "fill" parameter to mark which blocks have
 non-zero content for folding.
As a consequence, if a set of blocks on one side of a split has
 collapsed, _no_ folding is done: the result would be zero anyway,
 except for short blocks with SPREAD_AGGRESSIVE that are split down
 to a single block, but a) that means a lot of bits were available
 so a collapse is unlikely and b) anti-collapse can fill the block
 anyway, if it's used.
This also means that if itheta==0 or itheta==16384, we no longer
 fold at all on that side (even with long blocks), since we'd be
 multiplying the result by zero anyway.
This commit is contained in:
Timothy B. Terriberry 2011-01-19 16:30:03 -08:00 • committed by Jean-Marc Valin
parent 87efe1df00
commit 21af73eb21
5 changed files with 127 additions and 41 deletions
Download patch file Download diff file Expand all files Collapse all files

28
libcelt/celt.c
View file

@ -792,6 +792,7 @@ int celt_encode_with_ec_float(CELTEncoder * restrict st, const celt_sig * pcm, i
VARDECL(int, offsets);
VARDECL(int, fine_priority);
VARDECL(int, tf_res);
VARDECL(unsigned char, collapse_masks);
celt_sig *_overlap_mem;
celt_sig *prefilter_mem;
celt_word16 *oldBandE, *oldLogE2;
@ -819,6 +820,7 @@ int celt_encode_with_ec_float(CELTEncoder * restrict st, const celt_sig * pcm, i
celt_int32 tell;
int prefilter_tapset=0;
int pf_on;
int anti_collapse_rsv;
int anti_collapse_on=0;
SAVE_STACK;
@ -1265,8 +1267,10 @@ int celt_encode_with_ec_float(CELTEncoder * restrict st, const celt_sig * pcm, i
ALLOC(pulses, st->mode->nbEBands, int);
ALLOC(fine_priority, st->mode->nbEBands, int);
/* bits = packet size - where we are - safety - anti-collapse*/
bits = (nbCompressedBytes*8<<BITRES) - ec_enc_tell(enc, BITRES) - 1 - (isTransient&&LM>=2 ? (1<<BITRES) : 0);
/* bits = packet size - where we are - safety*/
bits = (nbCompressedBytes*8<<BITRES) - ec_enc_tell(enc, BITRES) - 1;
anti_collapse_rsv = isTransient&&LM>=2&&bits>=(LM+2<<BITRES) ? (1<<BITRES) : 0;
bits -= anti_collapse_rsv;
codedBands = compute_allocation(st->mode, st->start, st->end, offsets,
alloc_trim, &intensity, &dual_stereo, bits, pulses, fine_quant,
fine_priority, C, LM, enc, 1, st->lastCodedBands);
@ -1286,11 +1290,12 @@ int celt_encode_with_ec_float(CELTEncoder * restrict st, const celt_sig * pcm, i
#endif
/* Residual quantisation */
quant_all_bands(1, st->mode, st->start, st->end, X, C==2 ? X+N : NULL,
ALLOC(collapse_masks, st->mode->nbEBands, unsigned char);
quant_all_bands(1, st->mode, st->start, st->end, X, C==2 ? X+N : NULL, collapse_masks,
bandE, pulses, shortBlocks, st->spread_decision, dual_stereo, intensity, tf_res, resynth,
nbCompressedBytes*8, enc, LM, codedBands);
if (isTransient && LM>=2)
if (anti_collapse_rsv > 0)
{
anti_collapse_on = st->consec_transient<2;
ec_enc_bits(enc, anti_collapse_on, 1);
@ -1311,7 +1316,7 @@ int celt_encode_with_ec_float(CELTEncoder * restrict st, const celt_sig * pcm, i
#endif
if (anti_collapse_on)
{
anti_collapse(st->mode, X, LM, C, N,
anti_collapse(st->mode, X, collapse_masks, LM, C, N,
st->start, st->end, oldBandE, oldLogE, oldLogE2, pulses, enc->rng);
}
@ -1882,6 +1887,7 @@ int celt_decode_with_ec_float(CELTDecoder * restrict st, const unsigned char *da
VARDECL(int, offsets);
VARDECL(int, fine_priority);
VARDECL(int, tf_res);
VARDECL(unsigned char, collapse_masks);
celt_sig *out_mem[2];
celt_sig *decode_mem[2];
celt_sig *overlap_mem[2];
@ -1905,6 +1911,7 @@ int celt_decode_with_ec_float(CELTDecoder * restrict st, const unsigned char *da
celt_int32 tell;
int dynalloc_logp;
int postfilter_tapset;
int anti_collapse_rsv;
int anti_collapse_on=0;
SAVE_STACK;
@ -2060,7 +2067,9 @@ int celt_decode_with_ec_float(CELTDecoder * restrict st, const unsigned char *da
alloc_trim = tell+(6<<BITRES) <= total_bits ?
ec_dec_icdf(dec, trim_icdf, 7) : 5;
bits = (len*8<<BITRES) - ec_dec_tell(dec, BITRES) - 1 - (isTransient&&LM>=2 ? (1<<BITRES) : 0);
bits = (len*8<<BITRES) - ec_dec_tell(dec, BITRES) - 1;
anti_collapse_rsv = isTransient&&LM>=2&&bits>=(LM+2<<BITRES) ? (1<<BITRES) : 0;
bits -= anti_collapse_rsv;
codedBands = compute_allocation(st->mode, st->start, st->end, offsets,
alloc_trim, &intensity, &dual_stereo, bits, pulses, fine_quant,
fine_priority, C, LM, dec, 0, 0);
@ -2068,11 +2077,12 @@ int celt_decode_with_ec_float(CELTDecoder * restrict st, const unsigned char *da
unquant_fine_energy(st->mode, st->start, st->end, bandE, oldBandE, fine_quant, dec, C);
/* Decode fixed codebook */
quant_all_bands(0, st->mode, st->start, st->end, X, C==2 ? X+N : NULL,
ALLOC(collapse_masks, st->mode->nbEBands, unsigned char);
quant_all_bands(0, st->mode, st->start, st->end, X, C==2 ? X+N : NULL, collapse_masks,
NULL, pulses, shortBlocks, spread_decision, dual_stereo, intensity, tf_res, 1,
len*8, dec, LM, codedBands);
if (isTransient && LM>=2)
if (anti_collapse_rsv > 0)
{
anti_collapse_on = ec_dec_bits(dec, 1);
}
@ -2081,7 +2091,7 @@ int celt_decode_with_ec_float(CELTDecoder * restrict st, const unsigned char *da
fine_quant, fine_priority, len*8-ec_dec_tell(dec, 0), dec, C);
if (anti_collapse_on)
anti_collapse(st->mode, X, LM, C, N,
anti_collapse(st->mode, X, collapse_masks, LM, C, N,
st->start, st->end, oldBandE, oldLogE, oldLogE2, pulses, dec->rng);
log2Amp(st->mode, st->start, st->end, bandE, oldBandE, C);