This provides more entropy and allows some more flexibility on the
encoder side.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

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 looks for bands in each short block that have no energy. For
each of these "collapsed" bands, noise is injected to have an
energy equal to the minimum of the two previous frames for that band.
The mechanism can be used whenever there are 4 or more MDCTs (otherwise
no complete collapse is possible) and is signalled with one bit just
before the final fine energy bits.

Based on spreading_decision()'s logic. We choose tapsets
with less roll-off when we think the HF are tonal.

Supporting three different tapsets with different roll-offs. The default
is now a 5-tap post-filter with a 13 kHz cutoff frequency.

Gregory Maxwell authored 14 years ago and Jean-Marc Valin committed 14 years ago

In CVBR mode the rate selection was failing to add bytes which were about to fall off the end of the bitres and never be reusable, causing undershoot.

In case start or end changes, we want the encoder and decoder
to be in sync and not do anything stupid.

Nor scaling the mid only after we've been able to store it
for folding.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

Adds a new bitexact_log2tan() function which is much simpler, and
 more accurate.
The new approximation has an RMS error of 0.0038 bits from the
 correctly rounded result over the range of inputs we use, compared
 to an RMS error of 0.013 for the old log2_frac() method.
The actual computation of delta is also changed to use FRAC_MUL16,
 since this allows us to keep the full accuracy of the new method
 while avoiding 16-bit overflow.
The old delta computation actually could overflow 16 bits: it needed
 8 for the log2_frac() result, 1 for the sign of the difference, and
 8 more for N.

Also removes the 8 byte/packet lower bound

Previously, recombining only worked when going all the way back to
frequency domain.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

The right amount of data was being written for the first frame, but
 from the wrong offset in the buffer.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

This patch makes all symbols conditional on whether or not there's
 enough space left in the buffer to code them, and eliminates much
 of the redundancy in the side information.

A summary of the major changes:
* The isTransient flag is moved up to before the the coarse energy.
  If there are not enough bits to code the coarse energy, the flag
   would get forced to 0, meaning what energy values were coded
   would get interpreted incorrectly.
  This might not be the end of the world, and I'd be willing to
   move it back given a compelling argument.
* Coarse energy switches coding schemes when there are less than 15
   bits left in the packet:
  - With at least 2 bits remaining, the change in energy is forced
     to the range [-1...1] and coded with 1 bit (for 0) or 2 bits
     (for +/-1).
  - With only 1 bit remaining, the change in energy is forced to
     the range [-1...0] and coded with one bit.
  - If there is less than 1 bit remaining, the change in energy is
     forced to -1.
    This effectively low-passes bands whose energy is consistently
     starved; this might be undesirable, but letting the default be
     zero is unstable, which is worse.
* The tf_select flag gets moved back after the per-band tf_res
   flags again, and is now skipped entirely when none of the
   tf_res flags are set, and the default value is the same for
   either alternative.
* dynalloc boosting is now limited so that it stops once it's given
   a band all the remaining bits in the frame, or when it hits the
   "stupid cap" of (64<<LM)*(C<<BITRES) used during allocation.
* If dynalloc boosing has allocated all the remaining bits in the
   frame, the alloc trim parameter does not get encoded (it would
   have no effect).
* The intensity stereo offset is now limited to the range
   [start...codedBands], and thus doesn't get coded until after
   all of the skip decisions.
  Some space is reserved for it up front, and gradually given back
   as each band is skipped.
* The dual stereo flag is coded only if intensity>start, since
   otherwise it has no effect.
  It is now coded after the intensity flag.
* The space reserved for the final skip flag, the intensity stereo
   offset, and the dual stereo flag is now redistributed to all
   bands equally if it is unused.
  Before, the skip flag's bit was given to the band that stopped
   skipping without it (usually a dynalloc boosted band).

In order to enable simple interaction between VBR and these
 packet-size enforced limits, many of which are encountered before
 VBR is run, the maximum packet size VBR will allow is computed at
 the beginning of the encoding function, and the buffer reduced to
 that size immediately.
Later, when it is time to make the VBR decision, the minimum packet
 size is set high enough to ensure that no decision made thus far
 will have been affected by the packet size.
As long as this is smaller than the up-front maximum, all of the
 encoder's decisions will remain in-sync with the decoder.
If it is larger than the up-front maximum, the packet size is kept
 at that maximum, also ensuring sync.
The minimum used now is slightly larger than it used to be, because
 it also includes the bits added for dynalloc boosting.
Such boosting is shut off by the encoder at low rates, and so
 should not cause any serious issues at the rates where we would
 actually run out of room before compute_allocation().

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

There were two different ones in use, one with less precision than
 a float, and the other missing a digit in the middle.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

B contains the number of blocks _after_ splitting.
We were using it to decide a) when to use a uniform PDF instead of a
 triangular one for theta and b) whether to bias the bit allocation
 towards the lower bins.
Using B0 (the number of blocks before the split) instead for a)
 gives a PEAQ gain of 0.003 ODG (as high as 0.1 ODG on s02a samples
 006, 083, and 097) for 240-sample frames at 96kbps mono.
Using B0 instead for b) gives a gain of only 0.00002.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

The mid = (lo+hi)>>1 line in the binary search would allow hi to drop
 down to the same value as lo, meaning the rounding after the search
 would be choosing between the same two values.
This patch changes it to (lo+hi+1)>>1.
This will allow lo to increase up to the value hi, but only in the
 case that we can't possibly allocate enough pulses to meet the
 target number of bits (in which case the rounding doesn't matter).
To pay for the extra add, this moves the +1 in the comparison to bits
 to the other side, which can then be taken outside the loop.
The compiler can't normally do this because it might cause overflow
 which would change the results.

This rarely mattered, but gives a 0.01 PEAQ improvement on 12-byte
 120 sample frames.
It also makes the search process describable with a simple
 algorithm, rather than relying on this particular optimized
 implementation.
I.e., the binary search loop can now be replaced with
  for(lo=0;lo+1<cache[0]&&cache[lo+1]<bits;lo++);
  hi=lo+1;
 and it will give equivalent results.
This was not true before.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

This renames ec_dec_cdf() to ec_dec_icdf(), and changes the
 functionality to use an "inverse" CDF table, where
 icdf[i]=ft-cdf[i+1].
The first entry is omitted entirely.
It also adds a corresonding ec_enc_icdf() to the encoder, which uses
 the same table.
One could use ec_encode_bin() by converting the values in the tables
 back to normal CDF values, but the icdf[] table already has them in
 the form ec_encode_bin() wants to use them, so there's no reason to
 translate them and then translate them back.

This is done primarily to allow SILK to use the range coder with
 8-bit probability tables containing cumulative frequencies that
 span the full range 0...256.
With an 8-bit table, the final 256 of a normal CDF becomes 0 in the
 "inverse" CDF.
It's the 0 at the start of a normal CDF which would become 256, but
 this is the value we omit, as it already has to be special-cased in
 the encoder, and is not used at all in the decoder.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

The band where intensity stereo begins was being coded as an
 absolute value, rather than relative to start, even though the
 range of values in the bitstream was limited as if it was being
 coded relative to start (meaning there would be desync if
 intensity was sufficiently large).

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

Previously it was coded for all bands, even when not all of them
 were being used.

Timothy B. Terriberry authored 14 years ago and Jean-Marc Valin committed 14 years ago

The valid bands range from [start,end) everywhere, with start<end.
Therefore end should never be 0, and should be allowed to extend
 all the way to mode->nbEBands.
This patch does _not_ enforce that start<end, and it does _not_
 handle clearing oldBandE[] when the valid range changes, which
 are separate issues.