ref: 243ff0c63bf2ee33711a94204c10d79b7a12d57b
parent: 0734cad597afabc4d0080fbf435010c03d1a6f33
author: Jean-Marc Valin <[email protected]>
date: Tue May 3 13:06:54 EDT 2011
comments
--- a/src/opus_encoder.c
+++ b/src/opus_encoder.c
@@ -118,10 +118,12 @@
int to_celt = 0;
celt_int32 mono_rate;
+ /* Rete-dependent mono-stereo decision */
if (st->channels == 2)
{celt_int32 decision_rate;
decision_rate = st->bitrate_bps + st->voice_ratio*st->voice_ratio;
+ /* Add some hysteresis */
if (st->stream_channels == 2)
decision_rate += 4000;
else
@@ -145,7 +147,9 @@
if (st->user_mode==OPUS_MODE_AUTO)
{celt_int32 decision_rate;
+ /* SILK/CELT threshold is higher for voice than for music */
decision_rate = mono_rate - 3*st->voice_ratio*st->voice_ratio;
+ /* Hysteresis */
if (st->prev_mode == MODE_CELT_ONLY)
decision_rate += 4000;
else if (st->prev_mode>0)
@@ -161,7 +165,7 @@
st->mode = MODE_CELT_ONLY;
}
- /* Bandwidth selection */
+ /* Automatic (rate-dependent) bandwidth selection */
if (st->mode == MODE_CELT_ONLY)
{if (mono_rate>35000 || (mono_rate>28000 && st->bandwidth==BANDWIDTH_FULLBAND))
@@ -184,10 +188,14 @@
st->bandwidth = BANDWIDTH_MEDIUMBAND;
else
st->bandwidth = BANDWIDTH_NARROWBAND;
+ /* Prevents any transition to SWB/FB until the SILK layer has fully
+ switched to WB mode and turned the variable LP filter off */
if (!st->silk_mode.inWBmodeWithoutVariableLP && st->bandwidth > BANDWIDTH_WIDEBAND)
st->bandwidth = BANDWIDTH_WIDEBAND;
}
+ /* Prevents Opus from wasting bits on frequencies that are above
+ the Nyquist rate of the input signal */
if (st->Fs <= 24000 && st->bandwidth > BANDWIDTH_SUPERWIDEBAND)
st->bandwidth = BANDWIDTH_SUPERWIDEBAND;
if (st->Fs <= 16000 && st->bandwidth > BANDWIDTH_WIDEBAND)
@@ -200,7 +208,7 @@
if (st->user_bandwidth != BANDWIDTH_AUTO)
st->bandwidth = st->user_bandwidth;
- /* Preventing non-sensical configurations */
+ /* Prevents nonsensical configurations, i.e. modes that don't exist */
if (frame_size < st->Fs/100 && st->mode != MODE_CELT_ONLY)
st->mode = MODE_CELT_ONLY;
if (frame_size > st->Fs/50 && st->mode != MODE_SILK_ONLY)