Define "weak transients" for low bitrate hybrid

These rely on TF rather than short windows to avoid partial collapse.
parent bcfe0f68
......@@ -226,7 +226,8 @@ void opus_custom_encoder_destroy(CELTEncoder *st)
static int transient_analysis(const opus_val32 * OPUS_RESTRICT in, int len, int C,
opus_val16 *tf_estimate, int *tf_chan, int low_rate)
opus_val16 *tf_estimate, int *tf_chan, int low_rate,
int *weak_transient)
{
int i;
VARDECL(opus_val16, tmp);
......@@ -256,6 +257,7 @@ static int transient_analysis(const opus_val32 * OPUS_RESTRICT in, int len, int
SAVE_STACK;
ALLOC(tmp, len, opus_val16);
*weak_transient = 0;
/* For lower bitrates, let's be more conservative and have a forward masking
decay of 3.3 dB/ms. This avoids having to code transients at very low
bitrate (mostly for hybrid), which can result in unstable energy and/or
......@@ -381,7 +383,12 @@ static int transient_analysis(const opus_val32 * OPUS_RESTRICT in, int len, int
}
}
is_transient = mask_metric>200;
/* For low bitrates, define "weak transients" that need to be
handled differently to avoid partial collapse. */
if (low_rate && is_transient && mask_metric<600) {
is_transient = 0;
*weak_transient = 1;
}
/* Arbitrary metric for VBR boost */
tf_max = MAX16(0,celt_sqrt(27*mask_metric)-42);
/* *tf_estimate = 1 + MIN16(1, sqrt(MAX16(0, tf_max-30))/20); */
......@@ -1388,6 +1395,7 @@ int celt_encode_with_ec(CELTEncoder * OPUS_RESTRICT st, const opus_val16 * pcm,
opus_val16 surround_trim = 0;
opus_int32 equiv_rate;
int hybrid;
int weak_transient = 0;
VARDECL(opus_val16, surround_dynalloc);
ALLOC_STACK;
......@@ -1605,7 +1613,7 @@ int celt_encode_with_ec(CELTEncoder * OPUS_RESTRICT st, const opus_val16 * pcm,
if (st->complexity >= 1 && !st->lfe)
{
isTransient = transient_analysis(in, N+overlap, CC,
&tf_estimate, &tf_chan, effectiveBytes<15);
&tf_estimate, &tf_chan, effectiveBytes<15, &weak_transient);
}
if (LM>0 && ec_tell(enc)+3<=total_bits)
{
......@@ -1784,6 +1792,14 @@ int celt_encode_with_ec(CELTEncoder * OPUS_RESTRICT st, const opus_val16 * pcm,
tf_select = tf_analysis(mode, effEnd, isTransient, tf_res, lambda, X, N, LM, tf_estimate, tf_chan);
for (i=effEnd;i<end;i++)
tf_res[i] = tf_res[effEnd-1];
} else if (hybrid && weak_transient)
{
/* For weak transients, we rely on the fact that improving time resolution using
TF on a long window is imperfect and will not result in an energy collapse at
low bitrate. */
for (i=0;i<end;i++)
tf_res[i] = 1;
tf_select=0;
} else if (hybrid && effectiveBytes<15)
{
/* For low bitrate hybrid, we force temporal resolution to 5 ms rather than 2.5 ms. */
......
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