give MIDIRegion a tempo/meter based on their SMF or the SMF standard (120, 4/4)

libs/ardour/ardour/midi_region.h

@@ -157,6 +157,8 @@ class LIBARDOUR_API MidiRegion : public Region
 	void model_shifted (timecnt_t qn_distance);
 	void model_automation_state_changed (Evoral::Parameter const &);
 
+	void set_tempo_stuff_from_source ();
+
 	std::set<Evoral::Parameter> _filtered_parameters; ///< parameters that we ask our source not to return when reading
 	PBD::ScopedConnection _model_connection;
 	PBD::ScopedConnection _model_shift_connection;

libs/ardour/midi_region.cc

@@ -70,6 +70,8 @@ MidiRegion::MidiRegion (const SourceList& srcs)
 	: Region (srcs)
 	, _ignore_shift (false)
 {
+	set_tempo_stuff_from_source ();
+
 	/* by default MIDI regions are transparent,
 	 * this should probably be set depending on use-case,
 	 * (eg. loop recording, vs copy/edit/paste)
@@ -106,6 +108,26 @@ MidiRegion::~MidiRegion ()
 {
 }
 
+void
+MidiRegion::set_tempo_stuff_from_source ()
+{
+	std::shared_ptr<Evoral::SMF> smf = std::dynamic_pointer_cast<Evoral::SMF> (midi_source ());
+	assert (smf);
+
+	bool provided;
+	Temporal::TempoMap::SharedPtr new_map (smf->tempo_map (provided));
+
+	if (!provided) {
+		new_map.reset (new Temporal::TempoMap());
+	}
+
+	Temporal::TempoPoint const tp (new_map->tempo_at (start()));
+	Temporal::MeterPoint const mp (new_map->meter_at (start()));
+
+	_tempo = tp;
+	_meter = mp;
+}
+
 /** Export the MIDI data of the MidiRegion to a new MIDI file (SMF).
  */
 bool