Non-diegetic support for Ambisonics Mapping 254.
Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
diff --git a/src/opus_multistream_encoder.c b/src/opus_multistream_encoder.c
index 2c4dca2..98e174b 100644
--- a/src/opus_multistream_encoder.c
+++ b/src/opus_multistream_encoder.c
@@ -132,6 +132,29 @@
return (opus_val32*)(void*)ptr;
}
+#ifdef ENABLE_EXPERIMENTAL_AMBISONICS
+static int validate_ambisonics(int nb_channels, int *nb_streams, int *nb_coupled_streams)
+{
+ int order_plus_one;
+ int acn_channels;
+ int nondiegetic_channels;
+
+ order_plus_one = isqrt32(nb_channels);
+ acn_channels = order_plus_one * order_plus_one;
+ nondiegetic_channels = nb_channels - acn_channels;
+
+ if (order_plus_one < 1 || order_plus_one > 15 ||
+ (nondiegetic_channels != 0 && nondiegetic_channels != 2))
+ return 0;
+
+ if (nb_streams)
+ *nb_streams = acn_channels + (nondiegetic_channels != 0);
+ if (nb_coupled_streams)
+ *nb_coupled_streams = nondiegetic_channels != 0;
+ return 1;
+}
+#endif
+
static int validate_encoder_layout(const ChannelLayout *layout)
{
int s;
@@ -423,8 +446,8 @@
#ifdef ENABLE_EXPERIMENTAL_AMBISONICS
} else if (mapping_family==254)
{
- nb_streams=channels;
- nb_coupled_streams=0;
+ if (!validate_ambisonics(channels, &nb_streams, &nb_coupled_streams))
+ return 0;
#endif
} else
return 0;
@@ -467,7 +490,17 @@
st->variable_duration = OPUS_FRAMESIZE_ARG;
for (i=0;i<st->layout.nb_channels;i++)
st->layout.mapping[i] = mapping[i];
- if (!validate_layout(&st->layout) || !validate_encoder_layout(&st->layout))
+ if (!validate_layout(&st->layout))
+ return OPUS_BAD_ARG;
+ if (mapping_type == MAPPING_TYPE_SURROUND &&
+ !validate_encoder_layout(&st->layout))
+ return OPUS_BAD_ARG;
+#ifdef ENABLE_EXPERIMENTAL_AMBISONICS
+ if (mapping_type == MAPPING_TYPE_AMBISONICS &&
+ !validate_ambisonics(st->layout.nb_channels, NULL, NULL))
+ return OPUS_BAD_ARG;
+#endif
+ )
return OPUS_BAD_ARG;
ptr = (char*)st + align(sizeof(OpusMSEncoder));
coupled_size = opus_encoder_get_size(2);
@@ -564,10 +597,12 @@
} else if (mapping_family==254)
{
int i;
- *streams=channels;
- *coupled_streams=0;
- for(i=0;i<channels;i++)
- mapping[i] = i;
+ if (!validate_ambisonics(channels, streams, coupled_streams))
+ return OPUS_BAD_ARG;
+ for(i = 0; i < (*streams - *coupled_streams); i++)
+ mapping[i] = i + (*coupled_streams * 2);
+ for(i = 0; i < *coupled_streams * 2; i++)
+ mapping[i + (*streams - *coupled_streams)] = i;
#endif
} else
return OPUS_UNIMPLEMENTED;
@@ -748,14 +783,19 @@
)
{
int i;
- int non_mono_rate;
int total_rate;
+ int directional_rate;
+ int nondirectional_rate;
+ int leftover_bits;
- /* The mono channel gets (rate_ratio_num / rate_ratio_den) times as many bits
- * as all other channels */
+ /* 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 num_channels = st->layout.nb_streams;
+ const int nb_channels = st->layout.nb_streams + st->layout.nb_coupled_streams;
+ const int nb_nondirectional_channels = st->layout.nb_coupled_streams * 2 + 1;
+ const int nb_directional_channels = st->layout.nb_streams - 1;
if (st->bitrate_bps==OPUS_AUTO)
{
@@ -763,25 +803,52 @@
(Fs+60*Fs/frame_size) + st->layout.nb_streams * 15000;
} else if (st->bitrate_bps==OPUS_BITRATE_MAX)
{
- total_rate = num_channels * 320000;
- } else {
+ total_rate = nb_channels * 320000;
+ } else
+ {
total_rate = st->bitrate_bps;
}
- /* Let y be the non-mono rate and let p, q be integers such that the mono
- * channel rate is (p/q) * y.
+ /* 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
- * (n - 1) y + (p/q) y = T
- * y = (T q) / (qn - q + p)
+ * T = (n - m) * y + m * m_rate
+ * Solving for y,
+ * y = (q * T) / (m * (p - q) + n * q)
*/
- non_mono_rate =
- total_rate * rate_ratio_den
- / (rate_ratio_den*num_channels + rate_ratio_num - rate_ratio_den);
+ directional_rate =
+ total_rate * rate_ratio_den
+ / (nb_nondirectional_channels * (rate_ratio_num - rate_ratio_den)
+ + nb_channels * rate_ratio_den);
- rate[0] = total_rate - (num_channels - 1) * non_mono_rate;
- for (i=1;i<st->layout.nb_streams;i++)
+ /* 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 */
+ for (i = 0; i < st->layout.nb_streams; i++)
{
- rate[i] = non_mono_rate;
+ 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;
+ }
}
}
#endif /* ENABLE_EXPERIMENTAL_AMBISONICS */