Desperate hack to align master-bus on export.

Another 90% solution which hopefully gives us another year :(
see comments Session::start_audio_export() for explanation.

libs/ardour/ardour/session.h

@@ -725,7 +725,7 @@ class LIBARDOUR_API Session : public PBD::StatefulDestructible, public PBD::Scop
 	boost::shared_ptr<ExportHandler> get_export_handler ();
 	boost::shared_ptr<ExportStatus> get_export_status ();
 
-	int start_audio_export (framepos_t position, bool realtime = false, bool region_export = false);
+	int start_audio_export (framepos_t position, bool realtime = false, bool region_export = false, bool comensate_master_latency = false);
 
 	PBD::Signal1<int, framecnt_t> ProcessExport;
 	static PBD::Signal2<void,std::string, std::string> Exported;

libs/ardour/export_handler.cc

@@ -28,6 +28,7 @@
 
 #include "ardour/audioengine.h"
 #include "ardour/audiofile_tagger.h"
+#include "ardour/audio_port.h"
 #include "ardour/debug.h"
 #include "ardour/export_graph_builder.h"
 #include "ardour/export_timespan.h"
@@ -192,6 +193,7 @@ ExportHandler::start_timespan ()
 	handle_duplicate_format_extensions();
 	bool realtime = current_timespan->realtime ();
 	bool region_export = true;
+	bool incl_master_bus = false;
 	for (ConfigMap::iterator it = timespan_bounds.first; it != timespan_bounds.second; ++it) {
 		// Filenames can be shared across timespans
 		FileSpec & spec = it->second;
@@ -204,6 +206,33 @@ ExportHandler::start_timespan ()
 			default:
 				break;
 		}
+#if 1 // hack alert -- align master bus, compensate master latency
+
+		/* there's no easier way to get this information here.
+		 * Ports are configured in the PortExportChannelSelector GUI,
+		 * This ExportHandler has no context of routes.
+		 */
+		boost::shared_ptr<Route> master_bus = session.master_out ();
+		if (master_bus) {
+			const PortSet& ps = master_bus->output ()->ports();
+
+			const ExportChannelConfiguration::ChannelList& channels = spec.channel_config->get_channels ();
+			for (ExportChannelConfiguration::ChannelList::const_iterator it = channels.begin(); it != channels.end(); ++it) {
+
+				boost::shared_ptr <PortExportChannel> pep = boost::dynamic_pointer_cast<PortExportChannel> (*it);
+				if (!pep) {
+					continue;
+				}
+				PortExportChannel::PortSet const& ports = pep->get_ports ();
+				for (PortExportChannel::PortSet::const_iterator it = ports.begin(); it != ports.end(); ++it) {
+					boost::shared_ptr<AudioPort> ap = (*it).lock();
+					if (ps.contains (ap)) {
+						incl_master_bus = true;
+					}
+				}
+			}
+		}
+#endif
 		graph_builder->add_config (spec, realtime);
 	}
 
@@ -216,7 +245,7 @@ ExportHandler::start_timespan ()
 	session.ProcessExport.connect_same_thread (process_connection, boost::bind (&ExportHandler::process, this, _1));
 	process_position = current_timespan->get_start();
 	// TODO check if it's a RegionExport.. set flag to skip  process_without_events()
-	session.start_audio_export (process_position, realtime, region_export);
+	session.start_audio_export (process_position, realtime, region_export, incl_master_bus);
 }
 
 void

libs/ardour/session_export.cc

@@ -104,7 +104,7 @@ Session::pre_export ()
 
 /** Called for each range that is being exported */
 int
-Session::start_audio_export (framepos_t position, bool realtime, bool region_export)
+Session::start_audio_export (framepos_t position, bool realtime, bool region_export, bool comensate_master_latency)
 {
 	if (!_exporting) {
 		pre_export ();
@@ -130,14 +130,24 @@ Session::start_audio_export (framepos_t position, bool realtime, bool region_exp
 	/* "worst_track_latency" is the correct value for stem-exports
 	 * see to Route::add_export_point(),
 	 *
-	 * for master-bus export, we'd need to add the master's latency.
+	 * For master-bus export, we also need to add the master's latency.
-	 * or actually longest-total-session-latency.
+	 * (or actually longest-total-session-latency - worst-track-latency)
+	 * to align the export to 00:00:00:00.
 	 *
-	 * We can't use worst_playback_latency because that includes
+	 * We must not use worst_playback_latency because that
-	 * includes external latencies and would overcompensate.
+	 * includes external (hardware) latencies and would overcompensate
+	 * during file-export.
+	 *
+	 * (this is all still very [w]hacky. Individual Bus and Track outputs
+	 * are not aligned but one can select them in the PortExportChannelSelector)
 	 */
 	_export_latency = worst_track_latency ();
 
+	boost::shared_ptr<Route> master = master_out ();
+	if (master && comensate_master_latency) {
+		_export_latency += master->signal_latency ();
+	}
+
 	if (region_export) {
 		_export_latency = 0;
 	}