Forces CELT-only mode for LFE (despite the rate) and "locks" most of the
CELT analysis:
- No transient or TF
- Band boost on first band
- Only first two bands get PVQ bits
- Forced energy decay after the first two bands
This left FEC disabled on the decoder side for all cases except concatenated
packets. Also fixes a FEC bug in opus_demo (wrong output buffer size
calculation).
- Properly apply the transient boost by counting all the bits in the cost
- Disable the post-filter for non-20-ms frames that follow a transient (applies
only to variable framesize)
The original code was causing parts of a sine sweep to be completely dropped
due to the 300 Hz margin and the hysteresis. Also, fixes scaling for the
analysis downmix when the input is 16-bit PCM.
opus_decode() and opus_multistream_decode() now apply soft clipping
before converting to 16-bit int. This should produce better a higher
quality result than hard clipping like we were doing before. The _float()
API isn't affected, but the clipping function is exported so users can
manually apply the soft clipping.
Variable duration option renamed to OPUS_SET_EXPERT_FRAME_DURATION,
with new API.
Also moves up the analysis to avoid having to do int->float conversion
on large buffers.
1) In cases where the SILK desired bandwidth went down, then quickly up, we
count get stuck in a mode with the LP variation going the wrong way.
2) Bandwidth detection can no longer force SILK to go below wideband to
avoid switches that require redundancy.
Detects a transient when the average band energy jumps by more than 6 dB
between two consecutive frames. This fixes some undetected transients on
Gainless' Muse_Breaks_Rmx sample.
The search is based on minimizing the bitrate increase due to transients
by considering we can reduce the "transient boost" by reducing the frame
size, at the cost of increasing the normal overhead.
By not reinitializing the stereo state during a switch, the old stereo
memory would create a false impulse (i.e. single sample) in the decoded audio.
This change affects the normative part of the decoder. Fortunately,
the modified decoder is still compliant with the specification because
it still easily passes the testvectors. For example, for the float decoder
at 48 kHz, the opus_compare (arbitrary) "quality score" changes from
from 99.9333% to 99.925%.
This improves quality of CELT->SILK switches by not having the SILK encoder
attempt to encode a discontinuity. Overall, it's a small PQ improvement,
confirmed by some listening.
The channel mapping family nested lists were hard to read.
Promoting each family description to a subsection makes it
more clear where one is in the document.
Also add suggested downmix matricies. These are what we're
currently using in opus-tools, opusfile, and Firefox.
Ascii-art matrices in 69 columns is hard.
