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, 1 insertions, 0 deletions

diff --git a/libs/ardour/wscript b/libs/ardour/wscript
index df28255d5e..1604803884 100644
--- a/libs/ardour/wscript
+++ b/libs/ardour/wscript
@@ -396,6 +396,7 @@ def build(bld):
                         'libaudiographer',
                         'libtemporal',
                         'liblua',
+                        'zita-resampler',
                         ]
     if bld.env['build_target'] != 'mingw':
         obj.uselib += ['DL']