Move vari-speed into backend (resample ports)

Previously Ardour used a /local/ per track vari-speed mechanism.
Now that the disk-reader is a latency-compensated processor, the speed
of each disk-reader would need to be maintained locally, offset by each
disk-reader's output latency. Furthermore each disk-reader may
produce a different number of samples, depending on its global alignment.

This commit introduces port-data resampling directly at the engine-level:
Up/down-sample all input ports at the beginning, and down/up-sample output
port-data using the inverse ratio at the end of the session's process
cycle.
The session itself is unaware of the speed-change, and only needs to
handle transport speeds {-1, 0, +1}.

This also allows for aligned cue-monitoring and vari-speed recording,
and also pitch-shifts synthesized MIDI along.

1 files changed, 53 insertions, 2 deletions

diff --git a/libs/ardour/port.cc b/libs/ardour/port.cc
index 81290aa021..b469194ea5 100644
--- a/libs/ardour/port.cc
+++ b/libs/ardour/port.cc
@@ -43,7 +43,9 @@ PBD::Signal0<void> Port::PortSignalDrop;
 bool         Port::_connecting_blocked = false;
 pframes_t    Port::_global_port_buffer_offset = 0;
 pframes_t    Port::_cycle_nframes = 0;
+double       Port::_speed_ratio = 1.0;
 std::string  Port::state_node_name = X_("Port");
+const uint32_t Port::_resampler_quality = 12;
 
 /* a handy define to shorten what would otherwise be a needlessly verbose
  * repeated phrase
@@ -350,7 +352,7 @@ Port::increment_port_buffer_offset (pframes_t nframes)
 }
 
 void
-Port::set_public_latency_range (LatencyRange& range, bool playback) const
+Port::set_public_latency_range (LatencyRange const& range, bool playback) const
 {
 	/* this sets the visible latency that the rest of the port system
 	   sees. because we do latency compensation, all (most) of our visible
@@ -363,7 +365,16 @@ Port::set_public_latency_range (LatencyRange& range, bool playback) const
 	                             (playback ? "PLAYBACK" : "CAPTURE")));;
 
 	if (_port_handle) {
-		port_engine.set_latency_range (_port_handle, playback, range);
+		LatencyRange r (range);
+		if (externally_connected ()) {
+#if 0
+			r.min *= _speed_ratio;
+			r.max *= _speed_ratio;
+#endif
+			r.min += (_resampler_quality - 1);
+			r.max += (_resampler_quality - 1);
+		}
+		port_engine.set_latency_range (_port_handle, playback, r);
 	}
 }
 
@@ -419,6 +430,14 @@ Port::public_latency_range (bool /*playback*/) const
 
 	if (_port_handle) {
 		r = port_engine.get_latency_range (_port_handle, sends_output() ? true : false);
+		if (externally_connected ()) {
+#if 0
+			r.min /= _speed_ratio;
+			r.max /= _speed_ratio;
+#endif
+			r.min += (_resampler_quality - 1);
+			r.max += (_resampler_quality - 1);
+		}
 
 		DEBUG_TRACE (DEBUG::Latency, string_compose (
 				     "GET PORT %1: %4 PUBLIC latency range %2 .. %3\n",
@@ -458,6 +477,14 @@ Port::get_connected_latency_range (LatencyRange& range, bool playback) const
 
                                 if (remote_port) {
                                         lr = port_engine.get_latency_range (remote_port, playback);
+                                        if (externally_connected ()) {
+#if 0
+                                          lr.min /= _speed_ratio;
+                                          lr.max /= _speed_ratio;
+#endif
+                                          lr.min += (_resampler_quality - 1);
+                                          lr.max += (_resampler_quality - 1);
+                                        }
 
                                         DEBUG_TRACE (DEBUG::Latency, string_compose (
                                                              "\t%1 <-> %2 : latter has latency range %3 .. %4\n",
@@ -564,6 +591,19 @@ Port::physically_connected () const
 	return port_engine.physically_connected (_port_handle);
 }
 
+bool
+Port::externally_connected () const
+{
+	if (!_port_handle) {
+		return false;
+	}
+
+	// TODO: When used with JACK, check if this port
+	// is connected to any non-ardour ports.
+
+	return port_engine.physically_connected (_port_handle);
+}
+
 XMLNode&
 Port::get_state () const
 {
@@ -621,3 +661,14 @@ Port::set_state (const XMLNode& node, int)
 
 	return 0;
 }
+
+/*static*/ void
+Port::set_speed_ratio (double s) {
+	/* see VMResampler::set_rratio() for min/max range */
+	_speed_ratio = std::min (16.0, std::max (0.5, s));
+}
+
+/*static*/ void
+Port::set_cycle_samplecnt (pframes_t n) {
+	_cycle_nframes = floor (n * _speed_ratio);
+}