Revisit surround rate allocation
Stereo now gets twice the "marginal allocation" compared to mono, but has
a 20 kb/s offset. This should be more realistic across a wide range of
bitrates.
diff --git a/src/opus_multistream_encoder.c b/src/opus_multistream_encoder.c
index 163e73c..89844cb 100644
--- a/src/opus_multistream_encoder.c
+++ b/src/opus_multistream_encoder.c
@@ -362,15 +362,22 @@
opus_int32 channel_rate;
opus_int32 Fs;
char *ptr;
+ int stream_offset;
+ int lfe_offset;
int coupled_ratio; /* Q8 */
int lfe_ratio; /* Q8 */
ptr = (char*)st + align(sizeof(OpusMSEncoder));
opus_encoder_ctl((OpusEncoder*)ptr, OPUS_GET_SAMPLE_RATE(&Fs));
- /* Should depend on the bitrate, for now we assume coupled streams get 60% more bits than mono */
- coupled_ratio = 410;
- /* Should depend on the bitrate, for now we assume LFE gets 1/12 the bits of mono */
+ /* We start by giving each stream (coupled or uncoupled) the same bitrate.
+ This models the main saving of coupled channels over uncoupled. */
+ stream_offset = 20000;
+ /* The LFE stream is an exception to the above and gets fewer bits. */
+ lfe_offset = 3500;
+ /* Coupled streams get twice the mono rate after the first 20 kb/s. */
+ coupled_ratio = 512;
+ /* Should depend on the bitrate, for now we assume LFE gets 1/8 the bits of mono */
lfe_ratio = 32;
/* Compute bitrate allocation between streams */
@@ -381,10 +388,17 @@
{
channel_rate = 300000;
} else {
- int total = ((st->layout.nb_streams-st->layout.nb_coupled_streams-(st->lfe_stream!=-1))<<8) /* mono */
- + coupled_ratio*st->layout.nb_coupled_streams /* stereo */
- + (st->lfe_stream!=-1)*lfe_ratio;
- channel_rate = 256*(st->bitrate_bps-2000)/total;
+ int nb_lfe;
+ int nb_uncoupled;
+ int nb_coupled;
+ int total;
+ nb_lfe = (st->lfe_stream!=-1);
+ nb_coupled = st->layout.nb_coupled_streams;
+ nb_uncoupled = st->layout.nb_streams-nb_coupled-nb_lfe;
+ total = (nb_uncoupled<<8) /* mono */
+ + coupled_ratio*nb_coupled /* stereo */
+ + nb_lfe*lfe_ratio;
+ channel_rate = 256*(st->bitrate_bps-lfe_offset*nb_lfe-stream_offset*(nb_coupled+nb_uncoupled))/total;
}
#ifndef FIXED_POINT
if (st->variable_duration==OPUS_FRAMESIZE_VARIABLE && frame_size != Fs/50)
@@ -398,14 +412,12 @@
for (i=0;i<st->layout.nb_streams;i++)
{
if (i<st->layout.nb_coupled_streams)
- rate[i] = channel_rate*coupled_ratio>>8;
+ rate[i] = stream_offset+(channel_rate*coupled_ratio>>8);
else if (i!=st->lfe_stream)
- rate[i] = channel_rate;
+ rate[i] = stream_offset+channel_rate;
else
- rate[i] = 2000+(channel_rate*lfe_ratio>>8);
+ rate[i] = lfe_offset+(channel_rate*lfe_ratio>>8);
}
-
-
}
/* Max size in case the encoder decides to return three frames */
