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.
commit ea807b68678dd76175def2c5eb006c6bdb16679e
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Wed Mar 25 23:24:41 2009 -0400
cleanup before merge
commit 73ad1a0202641be6a23903e464ece21fe332a131
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Sat Mar 21 00:02:16 2009 -0400
Some tuning of the new stereo
commit c05057eb57a7723045214a2f830fd561388ae48a
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Sun Mar 15 19:56:11 2009 -0400
fixed-point: atan2() converted
commit a8476cf8be55b0612d42df98d9807ca1335adfe3
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Sat Mar 14 23:10:04 2009 -0400
fixed-point: Getting the new stereo code working in fixed-point (still more
work left)
commit 70a452761a5ce15700664e7167886dce5914cbd0
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Mon Mar 2 23:36:25 2009 -0500
Coding left and right independently for lower bands
commit 4efd1e6385c7d036749080265a8d26668312b91b
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Sun Mar 1 23:56:46 2009 -0500
Removed the sqrt(C) from the normalisation, which simplifies a lot of things.
commit a4f3c5c60bc396bf644afa49b49e6b24ccf144f8
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Fri Feb 20 20:49:38 2009 -0500
Better point stereo calculation when we don't encode the side anyway
commit f08525de4739f4017d19ec2e2022883deda8f826
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Thu Feb 19 19:43:09 2009 -0500
Apparently, Timothy's calculations for fine energy allocation also apply
to the quantisation of theta.
commit 6548cffc9d3f996b8a8dbfab982f0da0bc6c2dc2
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Thu Feb 19 07:35:24 2009 -0500
Better handling of the "theta bits" and disabling the orthogonalize()
commit 7aa82c694967afa85dd30be8cc670663f98829fe
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Wed Feb 18 08:01:07 2009 -0500
tuning the new stereo
commit c2b780a773de66fd9613c7cd54c09b705fe9ce45
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Sun Feb 15 22:24:52 2009 -0500
The new stereo coupling actually decodes properly now.
commit 85513c203d773bebcf0a6055f953170d563d890c
Author: Jean-Marc Valin <jean-marc.valin@usherbrooke.ca>
Date: Sun Feb 15 21:31:16 2009 -0500
First attempt at a new "constrained" MS stereo scheme
