ref: c2a6ac4e341f7224ef8e30ad4e1eee79a516e069
parent: 38fca4a203a6759f2c90b86c84c4db087982ca81
author: Marcin Gorzel <gorzel@google.com>
date: Thu Aug 30 09:15:21 EDT 2018
Apply equal bit allocation to ambisonic channels Fixes issue #95 on GitHub. Signed-off-by: Felicia Lim <flim@google.com>
--- a/src/opus_multistream_encoder.c
+++ b/src/opus_multistream_encoder.c
@@ -742,20 +742,9 @@
{int i;
opus_int32 total_rate;
- opus_int32 directional_rate;
- opus_int32 nondirectional_rate;
- opus_int32 leftover_bits;
+ opus_int32 per_stream_rate;
- /* Each nondirectional channel gets (rate_ratio_num / rate_ratio_den) times
- * as many bits as all other ambisonics channels.
- */
- const int rate_ratio_num = 4;
- const int rate_ratio_den = 3;
const int nb_channels = st->layout.nb_streams + st->layout.nb_coupled_streams;
- /* The omnidirectional ambisonics and non-diegetic stereo channels */
- const int nb_nondirectional_channels = st->layout.nb_coupled_streams * 2 + 1;
- /* The remaining ambisonics channels */
- const int nb_directional_channels = nb_channels - nb_nondirectional_channels;
if (st->bitrate_bps==OPUS_AUTO)
{@@ -769,46 +758,12 @@
total_rate = st->bitrate_bps;
}
- /* Let y be the directional rate, m be the num of nondirectional channels
- * m = (s + 1)
- * and let p, q be integers such that the nondirectional rate is
- * m_rate = (p / q) * y
- * Also let T be the total bitrate to allocate. Then
- * T = (n - m) * y + m * m_rate
- * Solving for y,
- * y = (q * T) / (m * (p - q) + n * q)
- */
- directional_rate =
- total_rate * rate_ratio_den
- / (nb_nondirectional_channels * (rate_ratio_num - rate_ratio_den)
- + nb_channels * rate_ratio_den);
-
- /* Calculate the nondirectional rate.
- * m_rate = y * (p / q)
- */
- nondirectional_rate = directional_rate * rate_ratio_num / rate_ratio_den;
-
- /* Calculate the leftover from truncation error.
- * leftover = T - y * (n - m) - m_rate * m
- * Place leftover bits in omnidirectional channel.
- */
- leftover_bits = total_rate
- - directional_rate * nb_directional_channels
- - nondirectional_rate * nb_nondirectional_channels;
-
- /* Calculate rates for each channel */
+ /* Allocate equal number of bits to Ambisonic (uncoupled) and non-diegetic
+ * (coupled) streams */
+ per_stream_rate = total_rate / st->layout.nb_streams;
for (i = 0; i < st->layout.nb_streams; i++)
{- if (i < st->layout.nb_coupled_streams)
- {- rate[i] = nondirectional_rate * 2;
- } else if (i == st->layout.nb_coupled_streams)
- {- rate[i] = nondirectional_rate + leftover_bits;
- } else
- {- rate[i] = directional_rate;
- }
+ rate[i] = per_stream_rate;
}
}