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Better rate allocation for stereo SILK in hybrid mode

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SILK was being allocated too few bits for stereo hybrid, often resulting
in forced narrowing of the width. We now allocate more bits to SILK
and reduce the threshold for narrowing. This improves quality enough that
the bitrate threshold for switching to SILK can be increased to 44 kb/s.
This commit is contained in:
Jean-Marc Valin 2017-07-16 03:01:41 -04:00
parent 95c48711f6
commit f3cff05eeb
No known key found for this signature in database
GPG Key ID: 5E5DD9A36F9189C8
2 changed files with 13 additions and 5 deletions
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2
silk/stereo_LR_to_MS.c
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@ -109,7 +109,7 @@ void silk_stereo_LR_to_MS(
if( total_rate_bps < 1 ) {
total_rate_bps = 1;
}
min_mid_rate_bps = silk_SMLABB( 2000, fs_kHz, 900 );
min_mid_rate_bps = silk_SMLABB( 2000, fs_kHz, 600 );
silk_assert( min_mid_rate_bps < 32767 );
/* Default bitrate distribution: 8 parts for Mid and (5+3*frac) parts for Side. so: mid_rate = ( 8 / ( 13 + 3 * frac ) ) * total_ rate */
frac_3_Q16 = silk_MUL( 3, frac_Q16 );

16
src/opus_encoder.c
View File

@ -154,7 +154,7 @@ static const opus_int32 stereo_music_threshold = 24000;
static const opus_int32 mode_thresholds[2][2] = {
/* voice */ /* music */
{ 64000, 16000}, /* mono */
{ 36000, 16000}, /* stereo */
{ 44000, 16000}, /* stereo */
};
static const opus_int32 fec_thresholds[] = {
@ -762,7 +762,7 @@ static int decide_fec(int useInBandFEC, int PacketLoss_perc, int last_fec, int m
return 0;
}
static int compute_silk_rate_for_hybrid(int rate, int bandwidth, int frame20ms, int vbr, int fec) {
static int compute_silk_rate_for_hybrid(int rate, int bandwidth, int frame20ms, int vbr, int fec, int channels) {
int entry;
int i;
int N;
@ -779,6 +779,8 @@ static int compute_silk_rate_for_hybrid(int rate, int bandwidth, int frame20ms,
{32000, 22000, 22000, 28000, 28000},
{64000, 38000, 38000, 50000, 50000}
};
/* Do the allocation per-channel. */
rate /= channels;
entry = 1 + frame20ms + 2*fec;
N = sizeof(rate_table)/sizeof(rate_table[0]);
for (i=1;i<N;i++)
@ -805,6 +807,10 @@ static int compute_silk_rate_for_hybrid(int rate, int bandwidth, int frame20ms,
}
if (bandwidth==OPUS_BANDWIDTH_SUPERWIDEBAND)
silk_rate += 300;
silk_rate *= channels;
/* The CELT layer saves a bit more than SILK for stereo, so we boost SILK. */
if (channels == 2 && rate >= 12000)
silk_rate += 1000;
return silk_rate;
}
@ -1673,7 +1679,8 @@ opus_int32 opus_encode_native(OpusEncoder *st, const opus_val16 *pcm, int frame_
if( st->mode == MODE_HYBRID ) {
/* Base rate for SILK */
st->silk_mode.bitRate = compute_silk_rate_for_hybrid(total_bitRate,
curr_bandwidth, st->Fs == 50 * frame_size, st->use_vbr, st->silk_mode.LBRR_coded);
curr_bandwidth, st->Fs == 50 * frame_size, st->use_vbr, st->silk_mode.LBRR_coded,
st->stream_channels);
if (!st->energy_masking)
{
/* Increasingly attenuate high band when it gets allocated fewer bits */
@ -1788,7 +1795,8 @@ opus_int32 opus_encode_native(OpusEncoder *st, const opus_val16 *pcm, int frame_
{
/* Compute SILK bitrate corresponding to the max total bits available */
opus_int32 maxBitRate = compute_silk_rate_for_hybrid(st->silk_mode.maxBits*st->Fs / frame_size,
curr_bandwidth, st->Fs == 50 * frame_size, st->use_vbr, st->silk_mode.LBRR_coded);
curr_bandwidth, st->Fs == 50 * frame_size, st->use_vbr, st->silk_mode.LBRR_coded,
st->stream_channels);
st->silk_mode.maxBits = maxBitRate * frame_size / st->Fs;
}
}