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

In commit ffe10574 JM added a "done" flag to the allocation
 interpolation loop: whenver a band did not have enough bits to
 pass its threshold for receiving PVQ pulses, all of the rest of
 band were given just enough bits for fine energy only.
This patch implements JM's "backwards done" idea: instead work
 backwards, dropping bands until the first band that is over the
 threshold is encountered, and don't artificially reduce the
 allocation any more after that.
This is much more stable: we can continue to signal manual skips if
 we want to, but we aren't forced to skip a large number of bands
 because of an isolated hole in he allocation.

This makes low-bitrate 120-sample frames much less rough.
It also reduces the force skip threshold from
 alloc_floor+(1<<BITRES)+1 to just alloc_floor+(1<<BITRES), because
 the former can now cascade to cause many bands to be skipped.
The difference here is subtle, and increases signaling overhead by
 0.11% of the total bitrate, but Monty confirmed that removing the
 +1 reduces noise in the bass (i.e., in N=1 bands where such a skip
 could cascade).

Finally the 64*C<<BITRES<<LM ceiling is moved into the bisection
 search, instead of just being imposed afterwards, again because I
 wouldn't want to try to explain in a spec why they're different.

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

1) Continue to update left and percoeff if we skip all the way to the
    first band.
   This doesn't actually matter for correctness, but I don't want to
    try to explain in a spec why we aren't doing this.
2) Force all the bits in skipped bands to go to fine energy.
   Before some of them could continue to be given to pulses, even though no
    pulses would actually be allocate for them.

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

The margin of safety was supposed to be 1/8th bit, not 1 bit, and the
 bit we reserved to terminate skip signalling before was actually 8
 bits.
This patch updates the margin of safety to the correct value and
 accounts for the one bit (not 8) needed for skip signalling.
It also fixes the remainder calculation in the skip loop to work
 correctly when start>0.

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

Now that manual skipping is in the same loop as forced skipping, there
 is no reason to do all of one, then all of the other.
This ensures we won't propagate bits to bands that have almost nothing
 later in quant_all_bands() because we didn't have enough bits to
 signal them skipped.

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

This allows us to a) not pay a coding cost to avoid skipping bands that are
 stupid to skip (e.g., the first band, or bands that have so few bits that we
 wouldn't redistribute anything) and b) not reserve bits to pay that cost.

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

This moves more of the decisions about when to stop skipping bands into the
 encoder-specific branch, so they are not forced in the decoder (because there
 is currently no bit-savings from forcing them).
It also no longer requires an extra bit to code the fine energy in a skipped
 band: that was meant to account for the skip flag, but we already subtracted
 that.

Making sure we never waste bits due to band skip and also making
sure we don't skip bands "in the middle".

Now properly (I think) handling thresh[] and skipping

And fixed a post-filter bug for that special case.

This adds some side-information that can be used to change the
threshold freq arbitrarily.

Should be more robust to closely-spaced transients

This reduces waste at high bit-rate

celtenc now defaults to unconstrained VBR.

Also some code to select between constrained and unconstrained VBR

Left and right are coded independently.

Also, making per-band dynamic allocation less aggressive.

Bands that are intensity-coded also get less bits than the others

There's no explicit signaling for it yet.

Mimimum resolution is now 1/4 bit/sample instead of 3/8. The allocation
tilt now gives more LF bits for small frame sizes. There's also a new
"alternate" allocation that should soon replace the current one.

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

This tunes the entropy model for coarse energy introduced in commit
 c1c40a76.
It uses a constant set of parameters, tuned from about an hour and a
 half of randomly selected test data encoded for each frame size,
 prediction type (inter/intra), and band number.
These will be slightly sub-optimal for different frame sizes, but
 should be better than what we were using.

For inter, this saves an average of 2.8, 5.2, 7.1, and 6.7 bits/frame
 for frame sizes of 120, 240, 480, and 960, respectively.
For intra, this saves an average of 1.5, 3.0, 4.5, and 5.3 bits/frame
 (for the same frame sizes, respectively).