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, 2 insertions, 1 deletions

diff --git a/libs/ardour/port_manager.cc b/libs/ardour/port_manager.cc
index dfc1c64421..6d3336cabb 100644
--- a/libs/ardour/port_manager.cc
+++ b/libs/ardour/port_manager.cc
@@ -749,10 +749,11 @@ void
 PortManager::cycle_start (pframes_t nframes)
 {
 	Port::set_global_port_buffer_offset (0);
-        Port::set_cycle_samplecnt (nframes);
+	Port::set_cycle_samplecnt (nframes);
 
 	_cycle_ports = ports.reader ();
 
+	// TODO parallelize
 	for (Ports::iterator p = _cycle_ports->begin(); p != _cycle_ports->end(); ++p) {
 		p->second->cycle_start (nframes);
 	}