fix crash when copy'ing latent plugins
[ardour.git] / libs / ardour / tempo.cc
index 8599594b3ba451f8f8a9f91f6d97ae36c3aeebc7..11da2fc81d3892768dbc2efbd2c17bc439228465 100644 (file)
@@ -33,7 +33,7 @@
 #include "ardour/lmath.h"
 #include "ardour/tempo.h"
 
-#include "i18n.h"
+#include "pbd/i18n.h"
 #include <locale.h>
 
 using namespace std;
@@ -73,7 +73,7 @@ Meter::frames_per_bar (const Tempo& tempo, framecnt_t sr) const
 const string TempoSection::xml_state_node_name = "Tempo";
 
 TempoSection::TempoSection (const XMLNode& node)
-       : MetricSection (0.0, 0, MusicTime)
+       : MetricSection (0.0, 0, MusicTime, true)
        , Tempo (TempoMap::default_tempo())
        , _c_func (0.0)
        , _active (true)
@@ -179,13 +179,13 @@ TempoSection::get_state() const
        char buf[256];
        LocaleGuard lg;
 
-       snprintf (buf, sizeof (buf), "%f", pulse());
+       snprintf (buf, sizeof (buf), "%lf", pulse());
        root->add_property ("pulse", buf);
        snprintf (buf, sizeof (buf), "%li", frame());
        root->add_property ("frame", buf);
-       snprintf (buf, sizeof (buf), "%f", _beats_per_minute);
+       snprintf (buf, sizeof (buf), "%lf", _beats_per_minute);
        root->add_property ("beats-per-minute", buf);
-       snprintf (buf, sizeof (buf), "%f", _note_type);
+       snprintf (buf, sizeof (buf), "%lf", _note_type);
        root->add_property ("note-type", buf);
        snprintf (buf, sizeof (buf), "%s", movable()?"yes":"no");
        root->add_property ("movable", buf);
@@ -219,14 +219,14 @@ TempoSection::tempo_at_frame (const framepos_t& f, const framecnt_t& frame_rate)
 
 /** returns the zero-based frame (relative to session)
    where the tempo in whole pulses per minute occurs in this section.
-   beat b is only used for constant tempos.
+   pulse p is only used for constant tempos.
    note that the tempo map may have multiple such values.
 */
 framepos_t
-TempoSection::frame_at_tempo (const double& ppm, const double& b, const framecnt_t& frame_rate) const
+TempoSection::frame_at_tempo (const double& ppm, const double& p, const framecnt_t& frame_rate) const
 {
        if (_type == Constant || _c_func == 0.0) {
-               return ((b - pulse())  * frames_per_pulse (frame_rate))  + frame();
+               return ((p - pulse()) * frames_per_pulse (frame_rate))  + frame();
        }
 
        return minute_to_frame (time_at_pulse_tempo (ppm), frame_rate) + frame();
@@ -453,7 +453,7 @@ TempoSection::time_at_pulse (const double& pulse) const
 const string MeterSection::xml_state_node_name = "Meter";
 
 MeterSection::MeterSection (const XMLNode& node)
-       : MetricSection (0.0, 0, MusicTime), Meter (TempoMap::default_meter())
+       : MetricSection (0.0, 0, MusicTime, false), Meter (TempoMap::default_meter())
 {
        XMLProperty const * prop;
        LocaleGuard lg;
@@ -569,12 +569,12 @@ MeterSection::get_state() const
        root->add_property ("bbt", buf);
        snprintf (buf, sizeof (buf), "%lf", beat());
        root->add_property ("beat", buf);
-       snprintf (buf, sizeof (buf), "%f", _note_type);
+       snprintf (buf, sizeof (buf), "%lf", _note_type);
        root->add_property ("note-type", buf);
        snprintf (buf, sizeof (buf), "%li", frame());
        root->add_property ("frame", buf);
        root->add_property ("lock-style", enum_2_string (position_lock_style()));
-       snprintf (buf, sizeof (buf), "%f", _divisions_per_bar);
+       snprintf (buf, sizeof (buf), "%lf", _divisions_per_bar);
        root->add_property ("divisions-per-bar", buf);
        snprintf (buf, sizeof (buf), "%s", movable()?"yes":"no");
        root->add_property ("movable", buf);
@@ -586,20 +586,27 @@ MeterSection::get_state() const
 /*
   Tempo Map Overview
 
+  The Shaggs - Things I Wonder
+  https://www.youtube.com/watch?v=9wQK6zMJOoQ
+
   Tempo is the rate of the musical pulse.
   Meters divide the pulses into measures and beats.
 
-  Note that Tempo::beats_per_minute() has nothing to do with musical beats.
-  It should rather be thought of as tempo note divisions per minute.
+  TempoSections - provide pulses in the form of beats_per_minute() and note_type() where note_type is the division of a whole pulse,
+  and beats_per_minute is the number of note_types in one minute (unlike what its name suggests).
+  Note that Tempo::beats_per_minute() has nothing to do with musical beats. It has been left that way because
+  a shorter one hasn't been found yet (pulse_divisions_per_minute()?).
 
-  TempoSections, which are nice to think of in whole pulses per minute,
-  and MeterSecions which divide tempo pulses into measures (via divisions_per_bar)
-  and beats (via note_divisor) are used to form a tempo map.
+  MeterSecions - divide pulses into measures (via divisions_per_bar) and beats (via note_divisor).
+
+  Both tempos and meters have a pulse position and a frame position.
+  Meters also have a beat position, which is always 0.0 for the first meter.
   TempoSections and MeterSections may be locked to either audio or music (position lock style).
-  We construct the tempo map by first using the frame or pulse position (depending on position lock style) of each tempo.
-  We then use this pulse/frame layout to find the beat & pulse or frame position of each meter (again depending on lock style).
+  The lock style determines the 'true' position of the section wich is used to calculate the other postion parameters of the section.
 
-  Having done this, we can now find any one of tempo, beat, frame or pulse if a beat, frame, pulse or tempo is known.
+  The first tempo and first meter are special. they must move together, and must be locked to audio.
+  Audio locked tempos which lie before the first meter are made inactive.
+  They will be re-activated if the first meter is again placed before them.
 
   With tepo sections potentially being ramped, meters provide a way of mapping beats to whole pulses without
   referring to the tempo function(s) involved as the distance in whole pulses between a meter and a subsequent beat is
@@ -614,23 +621,55 @@ MeterSection::get_state() const
   Remembering that ramped tempo sections interact, it is important to avoid referring to any other tempos when moving tempo sections,
   Here, beats (meters) are used to determine the new pulse (see predict_tempo_position())
 
-  The first tempo and first meter are special. they must move together, and must be locked to audio.
-  Audio locked tempos which lie before the first meter are made inactive.
-  They will be re-activated if the first meter is again placed before them.
-
-  Both tempos and meters have a pulse position and a frame position.
-  Meters also have a beat position, which is always 0.0 for the first meter.
-
-  A tempo locked to music is locked to musical pulses.
-  A meter locked to music is locked to beats.
-
-  Recomputing the tempo map is the process where the 'missing' position
+  Recomputing the map is the process where the 'missing' position
   (tempo pulse or meter pulse & beat in the case of AudioTime, frame for MusicTime) is calculated.
+  We construct the tempo map by first using the frame or pulse position (depending on position lock style) of each tempo.
+  We then use this tempo map (really just the tempos) to find the pulse or frame position of each meter (again depending on lock style).
+
+  Having done this, we can now find any musical duration by selecting the tempo and meter covering the position (or tempo) in question
+  and querying its appropriate meter/tempo.
 
   It is important to keep the _metrics in an order that makes sense.
   Because ramped MusicTime and AudioTime tempos can interact with each other,
   reordering is frequent. Care must be taken to keep _metrics in a solved state.
   Solved means ordered by frame or pulse with frame-accurate precision (see check_solved()).
+
+  Music and Audio
+
+  Music and audio-locked objects may seem interchangeable on the surface, but when translating
+  between audio samples and beats, keep in mind that a sample is only a quantised approximation
+  of the actual time (in minutes) of a beat.
+  Thus if a gui user points to the frame occupying the start of a music-locked object on 1|3|0, it does not
+  mean that this frame is the actual location in time of 1|3|0.
+
+  You cannot use a frame measurement to determine beat distance except under special circumstances
+  (e.g. where the user has requested that a beat lie on a SMPTE frame or if the tempo is known to be constant over the duration).
+
+  This means is that a user operating on a musical grid must supply the desired beat position and/or current beat quantization in order for the
+  sample space the user is operating at to be translated correctly to the object.
+
+  The current approach is to interpret the supplied frame using the grid division the user has currently selected.
+  If the user has no musical grid set, they are actually operating in sample space (even SMPTE frames are rounded to audio frame), so
+  the supplied audio frame is interpreted as the desired musical location (beat_at_frame()).
+
+  tldr: Beat, being a function of time, has nothing to do with sample rate, but time quantization can get in the way of precision.
+
+  When frame_at_beat() is called, the position calculation is performed in pulses and minutes.
+  The result is rounded to audio frames.
+  When beat_at_frame() is called, the frame is converted to minutes, with no rounding performed on the result.
+
+  So :
+  frame_at_beat (beat_at_frame (frame)) == frame
+  but :
+  beat_at_frame (frame_at_beat (beat)) != beat due to the time quantization of frame_at_beat().
+
+  Doing the second one will result in a beat distance error of up to 0.5 audio samples.
+  So instead work in pulses and/or beats and only use beat position to caclulate frame position (e.g. after tempo change).
+  For audio-locked objects, use frame position to calculate beat position.
+
+  The above pointless example would then do:
+  beat_at_pulse (pulse_at_beat (beat)) to avoid rounding.
+
 */
 struct MetricSectionSorter {
     bool operator() (const MetricSection* a, const MetricSection* b) {
@@ -649,7 +688,7 @@ TempoMap::TempoMap (framecnt_t fr)
        _frame_rate = fr;
        BBT_Time start (1, 1, 0);
 
-       TempoSection *t = new TempoSection (0.0, 0, _default_tempo.beats_per_minute(), _default_tempo.note_type(), TempoSection::Constant, AudioTime);
+       TempoSection *t = new TempoSection (0.0, 0, _default_tempo.beats_per_minute(), _default_tempo.note_type(), TempoSection::Ramp, AudioTime);
        MeterSection *m = new MeterSection (0.0, 0, 0.0, start, _default_meter.divisions_per_bar(), _default_meter.note_divisor(), AudioTime);
 
        t->set_movable (false);
@@ -733,13 +772,13 @@ TempoMap::remove_meter (const MeterSection& tempo, bool complete_operation)
 bool
 TempoMap::remove_meter_locked (const MeterSection& meter)
 {
-       Metrics::iterator i;
 
-       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
-               TempoSection* t = 0;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                       if (meter.frame() == (*i)->frame()) {
-                               if (t->locked_to_meter()) {
+       if (meter.position_lock_style() == AudioTime) {
+               /* remove meter-locked tempo */
+               for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
+                       TempoSection* t = 0;
+                       if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                               if (t->locked_to_meter() && meter.frame() == (*i)->frame()) {
                                        delete (*i);
                                        _metrics.erase (i);
                                        break;
@@ -748,7 +787,7 @@ TempoMap::remove_meter_locked (const MeterSection& meter)
                }
        }
 
-       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
+       for (Metrics::iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
                if (dynamic_cast<MeterSection*> (*i) != 0) {
                        if (meter.frame() == (*i)->frame()) {
                                if ((*i)->movable()) {
@@ -941,18 +980,24 @@ TempoMap::add_tempo_locked (const Tempo& tempo, double pulse, framepos_t frame
 {
        TempoSection* t = new TempoSection (pulse, frame, tempo.beats_per_minute(), tempo.note_type(), type, pls);
        t->set_locked_to_meter (locked_to_meter);
+       bool solved = false;
 
        do_insert (t);
 
        if (recompute) {
                if (pls == AudioTime) {
-                       solve_map_frame (_metrics, t, t->frame());
+                       solved = solve_map_frame (_metrics, t, t->frame());
                } else {
-                       solve_map_pulse (_metrics, t, t->pulse());
+                       solved = solve_map_pulse (_metrics, t, t->pulse());
                }
                recompute_meters (_metrics);
        }
 
+       if (!solved && recompute) {
+               warning << "Adding tempo may have left the tempo map unsolved." << endmsg;
+               recompute_map (_metrics);
+       }
+
        return t;
 }
 
@@ -999,36 +1044,57 @@ TempoMap::replace_meter (const MeterSection& ms, const Meter& meter, const BBT_T
                        first_t.set_frame (first.frame());
                        first_t.set_pulse (0.0);
                        first_t.set_position_lock_style (AudioTime);
+                       recompute_map (_metrics);
                }
-               recompute_map (_metrics);
        }
+
        PropertyChanged (PropertyChange ());
 }
 
 MeterSection*
-TempoMap::add_meter_locked (const Meter& meter, double beat, const Timecode::BBT_Time& where, framepos_t frame, PositionLockStyle pls, bool recompute)
+TempoMap::add_meter_locked (const Meter& meter, double beat, const BBT_Time& where, framepos_t frame, PositionLockStyle pls, bool recompute)
 {
-       const MeterSection& prev_m = meter_section_at_locked  (_metrics, frame - 1);
+       const MeterSection& prev_m = meter_section_at_frame_locked  (_metrics, frame - 1);
        const double pulse = ((where.bars - prev_m.bbt().bars) * (prev_m.divisions_per_bar() / prev_m.note_divisor())) + prev_m.pulse();
+       TempoSection* mlt = 0;
 
        if (pls == AudioTime) {
                /* add meter-locked tempo */
-               add_tempo_locked (tempo_at_locked (_metrics, frame), pulse,  frame, TempoSection::Ramp, AudioTime, true, true);
+               mlt = add_tempo_locked (tempo_at_frame_locked (_metrics, frame), pulse,  frame, TempoSection::Ramp, AudioTime, true, true);
+
+               if (!mlt) {
+                       return 0;
+               }
+
        }
 
        MeterSection* new_meter = new MeterSection (pulse, frame, beat, where, meter.divisions_per_bar(), meter.note_divisor(), pls);
+       bool solved = false;
 
        do_insert (new_meter);
 
        if (recompute) {
 
                if (pls == AudioTime) {
-                       solve_map_frame (_metrics, new_meter, frame);
+                       solved = solve_map_frame (_metrics, new_meter, frame);
                } else {
-                       solve_map_bbt (_metrics, new_meter, where);
+                       solved = solve_map_bbt (_metrics, new_meter, where);
+                       /* required due to resetting the pulse of meter-locked tempi above.
+                          Arguably  solve_map_bbt() should use solve_map_pulse (_metrics, TempoSection) instead,
+                          but afaict this cannot cause the map to be left unsolved (these tempi are all audio locked).
+                       */
+                       recompute_map (_metrics);
                }
        }
 
+       if (!solved && recompute) {
+               /* if this has failed to solve, there is little we can do other than to ensure that
+                  the new map is recalculated.
+               */
+               warning << "Adding meter may have left the tempo map unsolved." << endmsg;
+               recompute_map (_metrics);
+       }
+
        return new_meter;
 }
 
@@ -1184,14 +1250,15 @@ TempoMap::first_tempo ()
        return *t;
 }
 void
-TempoMap::recompute_tempos (Metrics& metrics)
+TempoMap::recompute_tempi (Metrics& metrics)
 {
        TempoSection* prev_t = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
 
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->active()) {
                                continue;
                        }
@@ -1233,14 +1300,16 @@ TempoMap::recompute_meters (Metrics& metrics)
        MeterSection* prev_m = 0;
 
        for (Metrics::const_iterator mi = metrics.begin(); mi != metrics.end(); ++mi) {
-               if ((meter = dynamic_cast<MeterSection*> (*mi)) != 0) {
+               if (!(*mi)->is_tempo()) {
+                       meter = static_cast<MeterSection*> (*mi);
                        if (meter->position_lock_style() == AudioTime) {
                                double pulse = 0.0;
                                pair<double, BBT_Time> b_bbt;
                                TempoSection* meter_locked_tempo = 0;
                                for (Metrics::const_iterator ii = metrics.begin(); ii != metrics.end(); ++ii) {
                                        TempoSection* t;
-                                       if ((t = dynamic_cast<TempoSection*> (*ii)) != 0) {
+                                       if ((*ii)->is_tempo()) {
+                                               t = static_cast<TempoSection*> (*ii);
                                                if ((t->locked_to_meter() || !t->movable()) && t->frame() == meter->frame()) {
                                                        meter_locked_tempo = t;
                                                        break;
@@ -1272,24 +1341,24 @@ TempoMap::recompute_meters (Metrics& metrics)
                        } else {
                                /* MusicTime */
                                double pulse = 0.0;
-                               pair<double, BBT_Time> new_beat;
+                               pair<double, BBT_Time> b_bbt;
                                if (prev_m) {
                                        const double beats = (meter->bbt().bars - prev_m->bbt().bars) * prev_m->divisions_per_bar();
                                        if (beats + prev_m->beat() != meter->beat()) {
                                                /* reordering caused a bbt change */
-                                               new_beat = make_pair (beats + prev_m->beat()
+                                               b_bbt = make_pair (beats + prev_m->beat()
                                                                   , BBT_Time ((beats / prev_m->divisions_per_bar()) + prev_m->bbt().bars, 1, 0));
                                        } else {
-                                               new_beat = make_pair (beats + prev_m->beat(), meter->bbt());
+                                               b_bbt = make_pair (beats + prev_m->beat(), meter->bbt());
                                        }
                                        pulse = (beats / prev_m->note_divisor()) + prev_m->pulse();
                                } else {
                                        /* shouldn't happen - the first is audio-locked */
                                        pulse = pulse_at_beat_locked (metrics, meter->beat());
-                                       new_beat = make_pair (meter->beat(), meter->bbt());
+                                       b_bbt = make_pair (meter->beat(), meter->bbt());
                                }
 
-                               meter->set_beat (new_beat);
+                               meter->set_beat (b_bbt);
                                meter->set_pulse (pulse);
                                meter->set_frame (frame_at_pulse_locked (metrics, pulse));
                        }
@@ -1321,7 +1390,7 @@ TempoMap::recompute_map (Metrics& metrics, framepos_t end)
                return;
        }
 
-       recompute_tempos (metrics);
+       recompute_tempi (metrics);
        recompute_meters (metrics);
 }
 
@@ -1370,7 +1439,8 @@ TempoMap::metric_at (BBT_Time bbt) const
 
        for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
                MeterSection* mw;
-               if ((mw = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       mw = static_cast<MeterSection*> (*i);
                        BBT_Time section_start (mw->bbt());
 
                        if (section_start.bars > bbt.bars || (section_start.bars == bbt.bars && section_start.beats > bbt.beats)) {
@@ -1385,29 +1455,197 @@ TempoMap::metric_at (BBT_Time bbt) const
 }
 
 double
-TempoMap::pulse_at_beat (const double& beat) const
+TempoMap::beat_at_frame (const framecnt_t& frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       return pulse_at_beat_locked (_metrics, beat);
+       return beat_at_frame_locked (_metrics, frame);
 }
 
+/* meter / tempo section based */
 double
-TempoMap::pulse_at_beat_locked (const Metrics& metrics, const double& beat) const
+TempoMap::beat_at_frame_locked (const Metrics& metrics, const framecnt_t& frame) const
 {
+       const TempoSection& ts = tempo_section_at_frame_locked (metrics, frame);
        MeterSection* prev_m = 0;
+       MeterSection* next_m = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       if (prev_m && (*i)->frame() > frame) {
+                               next_m = static_cast<MeterSection*> (*i);
+                               break;
+                       }
+                       prev_m = static_cast<MeterSection*> (*i);
+               }
+       }
+       if (frame < prev_m->frame()) {
+               return 0.0;
+       }
+       const double beat = prev_m->beat() + (ts.pulse_at_frame (frame, _frame_rate) - prev_m->pulse()) * prev_m->note_divisor();
+
+       /* audio locked meters fake their beat */
+       if (next_m && next_m->beat() < beat) {
+               return next_m->beat();
+       }
+
+       return beat;
+}
+
+framepos_t
+TempoMap::frame_at_beat (const double& beat) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return frame_at_beat_locked (_metrics, beat);
+}
+
+/* meter & tempo section based */
+framepos_t
+TempoMap::frame_at_beat_locked (const Metrics& metrics, const double& beat) const
+{
+       MeterSection* prev_m = 0;
+       TempoSection* prev_t = 0;
+
+       MeterSection* m;
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (prev_m && m->beat() > beat) {
                                break;
                        }
                        prev_m = m;
                }
+       }
+
+       TempoSection* t;
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
+                       if (prev_t && ((t->pulse() - prev_m->pulse()) * prev_m->note_divisor()) + prev_m->beat() > beat) {
+                               break;
+                       }
+                       prev_t = t;
+               }
 
        }
-       double const ret = prev_m->pulse() + ((beat - prev_m->beat()) / prev_m->note_divisor());
-       return ret;
+
+       return prev_t->frame_at_pulse (((beat - prev_m->beat()) / prev_m->note_divisor()) + prev_m->pulse(), _frame_rate);
+}
+
+Tempo
+TempoMap::tempo_at_frame (const framepos_t& frame) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return tempo_at_frame_locked (_metrics, frame);
+}
+
+Tempo
+TempoMap::tempo_at_frame_locked (const Metrics& metrics, const framepos_t& frame) const
+{
+       TempoSection* prev_t = 0;
+
+       TempoSection* t;
+
+       for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
+                       if (!t->active()) {
+                               continue;
+                       }
+                       if ((prev_t) && t->frame() > frame) {
+                               /* t is the section past frame */
+                               const double ret_bpm = prev_t->tempo_at_frame (frame, _frame_rate) * prev_t->note_type();
+                               const Tempo ret_tempo (ret_bpm, prev_t->note_type());
+                               return ret_tempo;
+                       }
+                       prev_t = t;
+               }
+       }
+
+       const double ret = prev_t->beats_per_minute();
+       const Tempo ret_tempo (ret, prev_t->note_type ());
+
+       return ret_tempo;
+}
+
+/** returns the frame at which the supplied tempo occurs, or
+ *  the frame of the last tempo section (search exhausted)
+ *  only the position of the first occurence will be returned
+ *  (extend me)
+*/
+framepos_t
+TempoMap::frame_at_tempo (const Tempo& tempo) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return frame_at_tempo_locked (_metrics, tempo);
+}
+
+
+framepos_t
+TempoMap::frame_at_tempo_locked (const Metrics& metrics, const Tempo& tempo) const
+{
+       TempoSection* prev_t = 0;
+       const double tempo_ppm = tempo.beats_per_minute() / tempo.note_type();
+
+       Metrics::const_iterator i;
+
+       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
+               TempoSection* t;
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
+
+                       if (!t->active()) {
+                               continue;
+                       }
+
+                       const double t_ppm = t->beats_per_minute() / t->note_type();
+
+                       if (t_ppm == tempo_ppm) {
+                               return t->frame();
+                       }
+
+                       if (prev_t) {
+                               const double prev_t_ppm = prev_t->beats_per_minute() / prev_t->note_type();
+
+                               if ((t_ppm > tempo_ppm && prev_t_ppm < tempo_ppm) || (t_ppm < tempo_ppm && prev_t_ppm > tempo_ppm)) {
+                                       return prev_t->frame_at_tempo (tempo_ppm, prev_t->pulse(), _frame_rate);
+                               }
+                       }
+                       prev_t = t;
+               }
+       }
+
+       return prev_t->frame();
+}
+
+/** more precise than doing tempo_at_frame (frame_at_beat (b)),
+ *  as there is no intermediate frame rounding.
+ */
+Tempo
+TempoMap::tempo_at_beat (const double& beat) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       const MeterSection* prev_m = &meter_section_at_beat_locked (_metrics, beat);
+       const TempoSection* prev_t = &tempo_section_at_beat_locked (_metrics, beat);
+       const double note_type = prev_t->note_type();
+
+       return Tempo (prev_t->tempo_at_pulse (((beat - prev_m->beat()) / prev_m->note_divisor()) + prev_m->pulse()) * note_type, note_type);
+}
+
+double
+TempoMap::pulse_at_beat (const double& beat) const
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+       return pulse_at_beat_locked (_metrics, beat);
+}
+
+double
+TempoMap::pulse_at_beat_locked (const Metrics& metrics, const double& beat) const
+{
+       const MeterSection* prev_m = &meter_section_at_beat_locked (metrics, beat);
+
+       return prev_m->pulse() + ((beat - prev_m->beat()) / prev_m->note_divisor());
 }
 
 double
@@ -1424,7 +1662,8 @@ TempoMap::beat_at_pulse_locked (const Metrics& metrics, const double& pulse) con
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (prev_m && m->pulse() > pulse) {
                                if (((pulse - prev_m->pulse()) * prev_m->note_divisor()) + prev_m->beat() > m->beat()) {
                                        break;
@@ -1439,7 +1678,7 @@ TempoMap::beat_at_pulse_locked (const Metrics& metrics, const double& pulse) con
 }
 
 double
-TempoMap::pulse_at_frame (const framecnt_t& frame) const
+TempoMap::pulse_at_frame (const framepos_t& frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
        return pulse_at_frame_locked (_metrics, frame);
@@ -1447,14 +1686,15 @@ TempoMap::pulse_at_frame (const framecnt_t& frame) const
 
 /* tempo section based */
 double
-TempoMap::pulse_at_frame_locked (const Metrics& metrics, const framecnt_t& frame) const
+TempoMap::pulse_at_frame_locked (const Metrics& metrics, const framepos_t& frame) const
 {
        /* HOLD (at least) THE READER LOCK */
        TempoSection* prev_t = 0;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->active()) {
                                continue;
                        }
@@ -1473,7 +1713,7 @@ TempoMap::pulse_at_frame_locked (const Metrics& metrics, const framecnt_t& frame
        return pulses_in_section + prev_t->pulse();
 }
 
-framecnt_t
+framepos_t
 TempoMap::frame_at_pulse (const double& pulse) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
@@ -1481,7 +1721,7 @@ TempoMap::frame_at_pulse (const double& pulse) const
 }
 
 /* tempo section based */
-framecnt_t
+framepos_t
 TempoMap::frame_at_pulse_locked (const Metrics& metrics, const double& pulse) const
 {
        /* HOLD THE READER LOCK */
@@ -1491,7 +1731,8 @@ TempoMap::frame_at_pulse_locked (const Metrics& metrics, const double& pulse) co
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
 
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->active()) {
                                continue;
                        }
@@ -1503,76 +1744,9 @@ TempoMap::frame_at_pulse_locked (const Metrics& metrics, const double& pulse) co
                }
        }
        /* must be treated as constant, irrespective of _type */
-       double const pulses_in_section = pulse - prev_t->pulse();
-       double const dtime = pulses_in_section * prev_t->frames_per_pulse (_frame_rate);
-
-       framecnt_t const ret = (framecnt_t) floor (dtime) + prev_t->frame();
-
-       return ret;
-}
-
-double
-TempoMap::beat_at_frame (const framecnt_t& frame) const
-{
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       return beat_at_frame_locked (_metrics, frame);
-}
-
-/* meter / tempo section based */
-double
-TempoMap::beat_at_frame_locked (const Metrics& metrics, const framecnt_t& frame) const
-{
-       const TempoSection& ts = tempo_section_at_locked (metrics, frame);
-       MeterSection* prev_m = 0;
-       MeterSection* next_m = 0;
-
-       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (prev_m && m->frame() > frame) {
-                               next_m = m;
-                               break;
-                       }
-                       prev_m = m;
-               }
-       }
-       if (frame < prev_m->frame()) {
-               return 0.0;
-       }
-       const double beat = prev_m->beat() + (ts.pulse_at_frame (frame, _frame_rate) - prev_m->pulse()) * prev_m->note_divisor();
-
-       if (next_m && next_m->beat() < beat) {
-               return next_m->beat();
-       }
-
-       return beat;
-}
-
-framecnt_t
-TempoMap::frame_at_beat (const double& beat) const
-{
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       return frame_at_beat_locked (_metrics, beat);
-}
-
-/* meter section based */
-framecnt_t
-TempoMap::frame_at_beat_locked (const Metrics& metrics, const double& beat) const
-{
-       const TempoSection& prev_t = tempo_section_at_beat_locked (metrics, beat);
-       MeterSection* prev_m = 0;
+       double const dtime = (pulse - prev_t->pulse()) * prev_t->frames_per_pulse (_frame_rate);
 
-       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
-                       if (prev_m && m->beat() > beat) {
-                               break;
-                       }
-                       prev_m = m;
-               }
-       }
-
-       return prev_t.frame_at_pulse (((beat - prev_m->beat()) / prev_m->note_divisor()) + prev_m->pulse(), _frame_rate);
+       return (framecnt_t) floor (dtime) + prev_t->frame();
 }
 
 double
@@ -1593,9 +1767,11 @@ TempoMap::beat_at_bbt_locked (const Metrics& metrics, const Timecode::BBT_Time&
        /* because audio-locked meters have 'fake' integral beats,
           there is no pulse offset here.
        */
+       MeterSection* m;
+
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (prev_m) {
                                const double bars_to_m = (m->beat() - prev_m->beat()) / prev_m->divisions_per_bar();
                                if ((bars_to_m + (prev_m->bbt().bars - 1)) > (bbt.bars - 1)) {
@@ -1627,10 +1803,11 @@ TempoMap::bbt_at_beat_locked (const Metrics& metrics, const double& b) const
        MeterSection* prev_m = 0;
        const double beats = max (0.0, b);
 
-       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m = 0;
+       MeterSection* m = 0;
 
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (prev_m) {
                                if (m->beat() > beats) {
                                        /* this is the meter after the one our beat is on*/
@@ -1689,9 +1866,11 @@ TempoMap::pulse_at_bbt_locked (const Metrics& metrics, const Timecode::BBT_Time&
        /* because audio-locked meters have 'fake' integral beats,
           there is no pulse offset here.
        */
+       MeterSection* m;
+
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (prev_m) {
                                if (m->bbt().bars > bbt.bars) {
                                        break;
@@ -1703,7 +1882,7 @@ TempoMap::pulse_at_bbt_locked (const Metrics& metrics, const Timecode::BBT_Time&
 
        const double remaining_bars = bbt.bars - prev_m->bbt().bars;
        const double remaining_pulses = remaining_bars * prev_m->divisions_per_bar() / prev_m->note_divisor();
-       const double ret = remaining_pulses + prev_m->pulse();
+       const double ret = remaining_pulses + prev_m->pulse() + (((bbt.beats - 1) + (bbt.ticks / BBT_Time::ticks_per_beat)) / prev_m->note_divisor());
 
        return ret;
 }
@@ -1721,10 +1900,12 @@ TempoMap::bbt_at_pulse_locked (const Metrics& metrics, const double& pulse) cons
 {
        MeterSection* prev_m = 0;
 
+       MeterSection* m = 0;
+
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m = 0;
 
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
 
                        if (prev_m) {
                                double const pulses_to_m = m->pulse() - prev_m->pulse();
@@ -1767,25 +1948,107 @@ TempoMap::bbt_at_pulse_locked (const Metrics& metrics, const double& pulse) cons
        return ret;
 }
 
-void
-TempoMap::bbt_time (framepos_t frame, BBT_Time& bbt)
+BBT_Time
+TempoMap::bbt_at_frame (framepos_t frame)
 {
-
        if (frame < 0) {
+               BBT_Time bbt;
                bbt.bars = 1;
                bbt.beats = 1;
                bbt.ticks = 0;
                warning << string_compose (_("tempo map asked for BBT time at frame %1\n"), frame) << endmsg;
-               return;
+               return bbt;
        }
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       const double beat = beat_at_frame_locked (_metrics, frame);
 
-       bbt = bbt_at_beat_locked (_metrics, beat);
+       return bbt_at_frame_locked (_metrics, frame);
+}
+
+BBT_Time
+TempoMap::bbt_at_frame_rt (framepos_t frame)
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock, Glib::Threads::TRY_LOCK);
+
+       if (!lm.locked()) {
+               throw std::logic_error ("TempoMap::bbt_time_rt() could not lock tempo map");
+       }
+
+       return bbt_at_frame_locked (_metrics, frame);
+}
+
+Timecode::BBT_Time
+TempoMap::bbt_at_frame_locked (const Metrics& metrics, const framepos_t& frame) const
+{
+       if (frame < 0) {
+               BBT_Time bbt;
+               bbt.bars = 1;
+               bbt.beats = 1;
+               bbt.ticks = 0;
+               warning << string_compose (_("tempo map asked for BBT time at frame %1\n"), frame) << endmsg;
+               return bbt;
+       }
+
+       const TempoSection& ts = tempo_section_at_frame_locked (metrics, frame);
+       MeterSection* prev_m = 0;
+       MeterSection* next_m = 0;
+
+       MeterSection* m;
+
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
+                       if (prev_m && m->frame() > frame) {
+                               next_m = m;
+                               break;
+                       }
+                       prev_m = m;
+               }
+       }
+
+       double beat = prev_m->beat() + (ts.pulse_at_frame (frame, _frame_rate) - prev_m->pulse()) * prev_m->note_divisor();
+
+       /* handle frame before first meter */
+       if (frame < prev_m->frame()) {
+               beat = 0.0;
+       }
+       /* audio locked meters fake their beat */
+       if (next_m && next_m->beat() < beat) {
+               beat = next_m->beat();
+       }
+
+       beat = max (0.0, beat);
+
+       const double beats_in_ms = beat - prev_m->beat();
+       const uint32_t bars_in_ms = (uint32_t) floor (beats_in_ms / prev_m->divisions_per_bar());
+       const uint32_t total_bars = bars_in_ms + (prev_m->bbt().bars - 1);
+       const double remaining_beats = beats_in_ms - (bars_in_ms * prev_m->divisions_per_bar());
+       const double remaining_ticks = (remaining_beats - floor (remaining_beats)) * BBT_Time::ticks_per_beat;
+
+       BBT_Time ret;
+
+       ret.ticks = (uint32_t) floor (remaining_ticks + 0.5);
+       ret.beats = (uint32_t) floor (remaining_beats);
+       ret.bars = total_bars;
+
+       /* 0 0 0 to 1 1 0 - based mapping*/
+       ++ret.bars;
+       ++ret.beats;
+
+       if (ret.ticks >= BBT_Time::ticks_per_beat) {
+               ++ret.beats;
+               ret.ticks -= BBT_Time::ticks_per_beat;
+       }
+
+       if (ret.beats >= prev_m->divisions_per_bar() + 1) {
+               ++ret.bars;
+               ret.beats = 1;
+       }
+
+       return ret;
 }
 
 framepos_t
-TempoMap::frame_time (const BBT_Time& bbt)
+TempoMap::frame_at_bbt (const BBT_Time& bbt)
 {
        if (bbt.bars < 1) {
                warning << string_compose (_("tempo map asked for frame time at bar < 1  (%1)\n"), bbt) << endmsg;
@@ -1797,12 +2060,12 @@ TempoMap::frame_time (const BBT_Time& bbt)
        }
        Glib::Threads::RWLock::ReaderLock lm (lock);
 
-       return frame_time_locked (_metrics, bbt);
+       return frame_at_bbt_locked (_metrics, bbt);
 }
 
-/* meter section based */
+/* meter & tempo section based */
 framepos_t
-TempoMap::frame_time_locked (const Metrics& metrics, const BBT_Time& bbt) const
+TempoMap::frame_at_bbt_locked (const Metrics& metrics, const BBT_Time& bbt) const
 {
        /* HOLD THE READER LOCK */
 
@@ -1819,32 +2082,50 @@ TempoMap::check_solved (const Metrics& metrics) const
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
                MeterSection* m;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->active()) {
                                continue;
                        }
                        if (prev_t) {
+                               /* check ordering */
                                if ((t->frame() <= prev_t->frame()) || (t->pulse() <= prev_t->pulse())) {
                                        return false;
                                }
 
-                               /* precision check ensures pulses and frames align.*/
-                               if (t->frame() != prev_t->frame_at_pulse (t->pulse(), _frame_rate)) {
+                               /* precision check ensures tempo and frames align.*/
+                               if (t->frame() != prev_t->frame_at_tempo (t->pulses_per_minute(), t->pulse(), _frame_rate)) {
                                        if (!t->locked_to_meter()) {
                                                return false;
                                        }
                                }
+
+                               /* gradient limit - who knows what it should be?
+                                  things are also ok (if a little chaotic) without this
+                               */
+                               if (fabs (prev_t->c_func()) > 1000.0) {
+                                       //std::cout << "c : " << prev_t->c_func() << std::endl;
+                                       return false;
+                               }
                        }
                        prev_t = t;
                }
 
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (prev_m && m->position_lock_style() == AudioTime) {
-                               TempoSection* t = const_cast<TempoSection*>(&tempo_section_at_locked (metrics, m->frame() - 1));
-                               const double nascent_m_pulse = ((m->beat() - prev_m->beat()) / prev_m->note_divisor()) + prev_m->pulse();
-                               const framepos_t nascent_m_frame = t->frame_at_pulse (nascent_m_pulse, _frame_rate);
-
-                               if (t && (nascent_m_frame > m->frame() || nascent_m_frame < 0)) {
+                               const TempoSection* t = &tempo_section_at_frame_locked (metrics, m->frame() - 1);
+                               const framepos_t nascent_m_frame = t->frame_at_pulse (m->pulse(), _frame_rate);
+                               /* Here we check that a preceding section of music doesn't overlap a subsequent one.
+                                  It is complicated by the fact that audio locked meters represent a discontinuity in the pulse
+                                  (they place an exact pulse at a particular time expressed only in frames).
+                                  This has the effect of shifting the calculated frame at the meter pulse (wrt the previous section of music)
+                                  away from its actual frame (which is now the frame location of the exact pulse).
+                                  This can result in the calculated frame (from the previous musical section)
+                                  differing from the exact frame by one sample.
+                                  Allow for that.
+                               */
+                               if (t && (nascent_m_frame > m->frame() + 1 || nascent_m_frame < 0)) {
                                        return false;
                                }
                        }
@@ -1862,7 +2143,8 @@ TempoMap::set_active_tempos (const Metrics& metrics, const framepos_t& frame)
 {
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->movable()) {
                                t->set_active (true);
                                continue;
@@ -1887,9 +2169,11 @@ TempoMap::solve_map_frame (Metrics& imaginary, TempoSection* section, const fram
        TempoSection* section_prev = 0;
        framepos_t first_m_frame = 0;
 
+       /* can't move a tempo before the first meter */
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
                MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (!m->movable()) {
                                first_m_frame = m->frame();
                                break;
@@ -1905,7 +2189,8 @@ TempoMap::solve_map_frame (Metrics& imaginary, TempoSection* section, const fram
 
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
                TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
 
                        if (!t->active()) {
                                continue;
@@ -1913,6 +2198,9 @@ TempoMap::solve_map_frame (Metrics& imaginary, TempoSection* section, const fram
                        if (prev_t) {
                                if (t == section) {
                                        section_prev = prev_t;
+                                       if (t->locked_to_meter()) {
+                                               prev_t = t;
+                                       }
                                        continue;
                                }
                                if (t->position_lock_style() == MusicTime) {
@@ -1936,16 +2224,20 @@ TempoMap::solve_map_frame (Metrics& imaginary, TempoSection* section, const fram
                }
        }
 
-       recompute_tempos (imaginary);
+#if (0)
+       recompute_tempi (imaginary);
 
        if (check_solved (imaginary)) {
                return true;
+       } else {
+               dunp (imaginary, std::cout);
        }
+#endif
 
        MetricSectionFrameSorter fcmp;
        imaginary.sort (fcmp);
 
-       recompute_tempos (imaginary);
+       recompute_tempi (imaginary);
 
        if (check_solved (imaginary)) {
                return true;
@@ -1964,7 +2256,8 @@ TempoMap::solve_map_pulse (Metrics& imaginary, TempoSection* section, const doub
 
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
                TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->active()) {
                                continue;
                        }
@@ -1997,16 +2290,20 @@ TempoMap::solve_map_pulse (Metrics& imaginary, TempoSection* section, const doub
                section->set_frame (section_prev->frame_at_pulse (pulse, _frame_rate));
        }
 
-       recompute_tempos (imaginary);
+#if (0)
+       recompute_tempi (imaginary);
 
        if (check_solved (imaginary)) {
                return true;
+       } else {
+               dunp (imaginary, std::cout);
        }
+#endif
 
        MetricSectionSorter cmp;
        imaginary.sort (cmp);
 
-       recompute_tempos (imaginary);
+       recompute_tempi (imaginary);
        /* Reordering
         * XX need a restriction here, but only for this case,
         * as audio locked tempos don't interact in the same way.
@@ -2028,7 +2325,7 @@ bool
 TempoMap::solve_map_frame (Metrics& imaginary, MeterSection* section, const framepos_t& frame)
 {
        /* disallow moving first meter past any subsequent one, and any movable meter before the first one */
-       const MeterSection* other =  &meter_section_at_locked (imaginary, frame);
+       const MeterSection* other =  &meter_section_at_frame_locked (imaginary, frame);
        if ((!section->movable() && other->movable()) || (!other->movable() && section->movable() && other->frame() >= frame)) {
                return false;
        }
@@ -2040,13 +2337,12 @@ TempoMap::solve_map_frame (Metrics& imaginary, MeterSection* section, const fram
                }
        }
 
-       /* it would make sense to bail out if there is no audio-locked meter,
-          however it may be desirable to move a music-locked meter by frame at some point.
-       */
        TempoSection* meter_locked_tempo = 0;
+
        for (Metrics::const_iterator ii = imaginary.begin(); ii != imaginary.end(); ++ii) {
                TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*ii)) != 0) {
+               if ((*ii)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*ii);
                        if ((t->locked_to_meter() || !t->movable()) && t->frame() == section->frame()) {
                                meter_locked_tempo = t;
                                break;
@@ -2065,7 +2361,8 @@ TempoMap::solve_map_frame (Metrics& imaginary, MeterSection* section, const fram
 
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
                MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (m == section){
                                if (prev_m && section->movable()) {
                                        const double beats = (pulse_at_frame_locked (imaginary, frame) - prev_m->pulse()) * prev_m->note_divisor();
@@ -2097,8 +2394,11 @@ TempoMap::solve_map_frame (Metrics& imaginary, MeterSection* section, const fram
                                                        return false;
                                                }
                                        } else {
-                                               /* all is ok. set section's tempo */
-                                               MeterSection* meter_copy = const_cast<MeterSection*> (&meter_section_at_locked (future_map, section->frame()));
+                                               /* all is ok. set section's locked tempo if allowed.
+                                                  possibly disallowed if there is an adjacent audio-locked tempo.
+                                                  XX this check could possibly go. its never actually happened here.
+                                               */
+                                               MeterSection* meter_copy = const_cast<MeterSection*> (&meter_section_at_frame_locked (future_map, section->frame()));
                                                meter_copy->set_frame (frame);
 
                                                if ((solved = solve_map_frame (future_map, tempo_copy, frame))) {
@@ -2171,7 +2471,8 @@ TempoMap::solve_map_bbt (Metrics& imaginary, MeterSection* section, const BBT_Ti
        /* disallow setting section to an existing meter's bbt */
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
                MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (m != section && m->bbt().bars == when.bars) {
                                return false;
                        }
@@ -2183,7 +2484,8 @@ TempoMap::solve_map_bbt (Metrics& imaginary, MeterSection* section, const BBT_Ti
 
        for (Metrics::iterator i = imaginary.begin(); i != imaginary.end(); ++i) {
                MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        pair<double, BBT_Time> b_bbt;
                        double new_pulse = 0.0;
 
@@ -2205,7 +2507,8 @@ TempoMap::solve_map_bbt (Metrics& imaginary, MeterSection* section, const BBT_Ti
 
                                for (Metrics::const_iterator ii = imaginary.begin(); ii != imaginary.end(); ++ii) {
                                        TempoSection* t;
-                                       if ((t = dynamic_cast<TempoSection*> (*ii)) != 0) {
+                                       if ((*ii)->is_tempo()) {
+                                               t = static_cast<TempoSection*> (*ii);
                                                if ((t->locked_to_meter() || !t->movable()) && t->frame() == m->frame()) {
                                                        meter_locked_tempo = t;
                                                        break;
@@ -2288,7 +2591,8 @@ TempoMap::copy_metrics_and_point (const Metrics& metrics, Metrics& copy, TempoSe
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
                MeterSection* m;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (t == section) {
                                ret = new TempoSection (*t);
                                copy.push_back (ret);
@@ -2298,7 +2602,8 @@ TempoMap::copy_metrics_and_point (const Metrics& metrics, Metrics& copy, TempoSe
                        TempoSection* cp = new TempoSection (*t);
                        copy.push_back (cp);
                }
-               if ((m = dynamic_cast<MeterSection *> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection *> (*i);
                        MeterSection* cp = new MeterSection (*m);
                        copy.push_back (cp);
                }
@@ -2315,12 +2620,14 @@ TempoMap::copy_metrics_and_point (const Metrics& metrics, Metrics& copy, MeterSe
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                TempoSection* t;
                MeterSection* m;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        TempoSection* cp = new TempoSection (*t);
                        copy.push_back (cp);
                }
 
-               if ((m = dynamic_cast<MeterSection *> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection *> (*i);
                        if (m == section) {
                                ret = new MeterSection (*m);
                                copy.push_back (ret);
@@ -2334,6 +2641,13 @@ TempoMap::copy_metrics_and_point (const Metrics& metrics, Metrics& copy, MeterSe
        return ret;
 }
 
+/** answers the question "is this a valid beat position for this tempo section?".
+ *  it returns true if the tempo section can be moved to the requested bbt position,
+ *  leaving the tempo map in a solved state.
+ * @param section the tempo section to be moved
+ * @param bbt the requested new position for the tempo section
+ * @return true if the tempo section can be moved to the position, otherwise false.
+ */
 bool
 TempoMap::can_solve_bbt (TempoSection* ts, const BBT_Time& bbt)
 {
@@ -2395,15 +2709,26 @@ TempoMap::predict_tempo_position (TempoSection* section, const BBT_Time& bbt)
 }
 
 void
-TempoMap::gui_move_tempo (TempoSection* ts, const framepos_t& frame)
+TempoMap::gui_move_tempo (TempoSection* ts, const framepos_t& frame, const int& sub_num)
 {
        Metrics future_map;
+       bool was_musical = ts->position_lock_style() == MusicTime;
+
+       if (sub_num == 0 && was_musical) {
+               /* if we're not snapping to music,
+                  AudioTime and MusicTime may be treated identically.
+               */
+               ts->set_position_lock_style (AudioTime);
+       }
 
        if (ts->position_lock_style() == MusicTime) {
                {
+                       /* if we're snapping to a musical grid, set the pulse exactly instead of via the supplied frame. */
                        Glib::Threads::RWLock::WriterLock lm (lock);
                        TempoSection* tempo_copy = copy_metrics_and_point (_metrics, future_map, ts);
-                       const double pulse = pulse_at_frame_locked (future_map, frame);
+                       const double beat = exact_beat_at_frame_locked (future_map, frame, sub_num);
+                       double pulse = pulse_at_beat_locked (future_map, beat);
+
                        if (solve_map_pulse (future_map, tempo_copy, pulse)) {
                                solve_map_pulse (_metrics, ts, pulse);
                                recompute_meters (_metrics);
@@ -2422,6 +2747,10 @@ TempoMap::gui_move_tempo (TempoSection* ts, const framepos_t& frame)
                }
        }
 
+       if (sub_num == 0 && was_musical) {
+               ts->set_position_lock_style (MusicTime);
+       }
+
        Metrics::const_iterator d = future_map.begin();
        while (d != future_map.end()) {
                delete (*d);
@@ -2444,7 +2773,7 @@ TempoMap::gui_move_meter (MeterSection* ms, const framepos_t& frame)
 
                        if (solve_map_frame (future_map, copy, frame)) {
                                solve_map_frame (_metrics, ms, frame);
-                               recompute_tempos (_metrics);
+                               recompute_tempi (_metrics);
                        }
                }
        } else {
@@ -2457,7 +2786,7 @@ TempoMap::gui_move_meter (MeterSection* ms, const framepos_t& frame)
 
                        if (solve_map_bbt (future_map, copy, bbt)) {
                                solve_map_bbt (_metrics, ms, bbt);
-                               recompute_tempos (_metrics);
+                               recompute_tempi (_metrics);
                        }
                }
        }
@@ -2480,7 +2809,7 @@ TempoMap::gui_change_tempo (TempoSection* ts, const Tempo& bpm)
                Glib::Threads::RWLock::WriterLock lm (lock);
                TempoSection* tempo_copy = copy_metrics_and_point (_metrics, future_map, ts);
                tempo_copy->set_beats_per_minute (bpm.beats_per_minute());
-               recompute_tempos (future_map);
+               recompute_tempi (future_map);
 
                if (check_solved (future_map)) {
                        ts->set_beats_per_minute (bpm.beats_per_minute());
@@ -2525,46 +2854,54 @@ TempoMap::gui_dilate_tempo (TempoSection* ts, const framepos_t& frame, const fra
                const frameoffset_t fr_off = end_frame - frame;
 
                if (prev_t && prev_t->pulse() > 0.0) {
-                       prev_to_prev_t = const_cast<TempoSection*>(&tempo_section_at_locked (future_map, prev_t->frame() - 1));
+                       prev_to_prev_t = const_cast<TempoSection*>(&tempo_section_at_frame_locked (future_map, prev_t->frame() - 1));
                }
 
                TempoSection* next_t = 0;
                for (Metrics::iterator i = future_map.begin(); i != future_map.end(); ++i) {
                        TempoSection* t = 0;
-                       if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+                       if ((*i)->is_tempo()) {
+                               t = static_cast<TempoSection*> (*i);
                                if (t->frame() > ts->frame()) {
                                        next_t = t;
                                        break;
                                }
                        }
                }
+               /* minimum allowed measurement distance in frames */
+               const framepos_t min_dframe = 2;
 
                /* the change in frames is the result of changing the slope of at most 2 previous tempo sections.
                   constant to constant is straightforward, as the tempo prev to prev_t has constant slope.
                */
                double contribution = 0.0;
-               double start_pulse = prev_t->pulse_at_frame (frame, _frame_rate);
 
                if (next_t && prev_to_prev_t && prev_to_prev_t->type() == TempoSection::Ramp) {
                        contribution = (prev_t->frame() - prev_to_prev_t->frame()) / (double) (next_t->frame() - prev_to_prev_t->frame());
                }
 
-               frameoffset_t prev_t_frame_contribution = fr_off - (contribution * (double) fr_off);
-               double end_pulse = prev_t->pulse_at_frame (end_frame, _frame_rate);
+               const frameoffset_t prev_t_frame_contribution = fr_off - (contribution * (double) fr_off);
+
+               const double start_pulse = prev_t->pulse_at_frame (frame, _frame_rate);
+               const double end_pulse = prev_t->pulse_at_frame (end_frame, _frame_rate);
+
                double new_bpm;
 
                if (prev_t->type() == TempoSection::Constant || prev_t->c_func() == 0.0) {
 
                        if (prev_t->position_lock_style() == MusicTime) {
                                if (prev_to_prev_t && prev_to_prev_t->type() == TempoSection::Ramp) {
+                                       if (frame > prev_to_prev_t->frame() + min_dframe && (frame + prev_t_frame_contribution) > prev_to_prev_t->frame() + min_dframe) {
 
-                                       new_bpm = prev_t->beats_per_minute() * ((frame - prev_to_prev_t->frame())
-                                                                               / (double) ((frame + prev_t_frame_contribution) - prev_to_prev_t->frame()));
-
+                                               new_bpm = prev_t->beats_per_minute() * ((frame - prev_to_prev_t->frame())
+                                                                                       / (double) ((frame + prev_t_frame_contribution) - prev_to_prev_t->frame()));
+                                       } else {
+                                               new_bpm = prev_t->beats_per_minute();
+                                       }
                                } else {
                                        /* prev to prev is irrelevant */
 
-                                       if (start_pulse != prev_t->pulse()) {
+                                       if (start_pulse > prev_t->pulse() && end_pulse > prev_t->pulse()) {
                                                new_bpm = prev_t->beats_per_minute() * ((start_pulse - prev_t->pulse()) / (end_pulse - prev_t->pulse()));
                                        } else {
                                                new_bpm = prev_t->beats_per_minute();
@@ -2573,12 +2910,17 @@ TempoMap::gui_dilate_tempo (TempoSection* ts, const framepos_t& frame, const fra
                        } else {
                                /* AudioTime */
                                if (prev_to_prev_t && prev_to_prev_t->type() == TempoSection::Ramp) {
-                                       new_bpm = prev_t->beats_per_minute() * ((frame - prev_t->frame())
-                                                                               / (double) ((frame + prev_t_frame_contribution) - prev_t->frame()));
+                                       if (frame > prev_to_prev_t->frame() + min_dframe && end_frame > prev_to_prev_t->frame() + min_dframe) {
+
+                                               new_bpm = prev_t->beats_per_minute() * ((frame - prev_to_prev_t->frame())
+                                                                                       / (double) ((end_frame) - prev_to_prev_t->frame()));
+                                       } else {
+                                               new_bpm = prev_t->beats_per_minute();
+                                       }
                                } else {
                                        /* prev_to_prev_t is irrelevant */
 
-                                       if (end_frame != prev_t->frame()) {
+                                       if (frame > prev_t->frame() + min_dframe && end_frame > prev_t->frame() + min_dframe) {
                                                new_bpm = prev_t->beats_per_minute() * ((frame - prev_t->frame()) / (double) (end_frame - prev_t->frame()));
                                        } else {
                                                new_bpm = prev_t->beats_per_minute();
@@ -2587,29 +2929,41 @@ TempoMap::gui_dilate_tempo (TempoSection* ts, const framepos_t& frame, const fra
                        }
                } else {
 
-                       double frame_ratio;
-                       double pulse_ratio;
+                       double frame_ratio = 1.0;
+                       double pulse_ratio = 1.0;
                        const framepos_t pulse_pos = prev_t->frame_at_pulse (pulse, _frame_rate);
 
                        if (prev_to_prev_t) {
-
-                               frame_ratio = (((pulse_pos - fr_off) - prev_to_prev_t->frame()) / (double) ((pulse_pos) - prev_to_prev_t->frame()));
-                               pulse_ratio = ((start_pulse - prev_to_prev_t->pulse()) / (end_pulse - prev_to_prev_t->pulse()));
+                               if (pulse_pos > prev_to_prev_t->frame() + min_dframe && (pulse_pos - fr_off) > prev_to_prev_t->frame() + min_dframe) {
+                                       frame_ratio = (((pulse_pos - fr_off) - prev_to_prev_t->frame()) / (double) ((pulse_pos) - prev_to_prev_t->frame()));
+                               }
+                               if (end_pulse > prev_to_prev_t->pulse() && start_pulse > prev_to_prev_t->pulse()) {
+                                       pulse_ratio = ((start_pulse - prev_to_prev_t->pulse()) / (end_pulse - prev_to_prev_t->pulse()));
+                               }
                        } else {
-
-                               frame_ratio = (((pulse_pos - fr_off) - prev_t->frame()) / (double) ((pulse_pos) - prev_t->frame()));
+                               if (pulse_pos > prev_t->frame() + min_dframe && (pulse_pos - fr_off) > prev_t->frame() + min_dframe) {
+                                       frame_ratio = (((pulse_pos - fr_off) - prev_t->frame()) / (double) ((pulse_pos) - prev_t->frame()));
+                               }
                                pulse_ratio = (start_pulse / end_pulse);
                        }
                        new_bpm = prev_t->beats_per_minute() * (pulse_ratio * frame_ratio);
                }
 
+               /* don't clamp and proceed here.
+                  testing has revealed that this can go negative,
+                  which is an entirely different thing to just being too low.
+               */
+               if (new_bpm < 0.5) {
+                       return;
+               }
+               new_bpm = min (new_bpm, (double) 1000.0);
                prev_t->set_beats_per_minute (new_bpm);
-               recompute_tempos (future_map);
+               recompute_tempi (future_map);
                recompute_meters (future_map);
 
                if (check_solved (future_map)) {
                        ts->set_beats_per_minute (new_bpm);
-                       recompute_tempos (_metrics);
+                       recompute_tempi (_metrics);
                        recompute_meters (_metrics);
                }
        }
@@ -2623,6 +2977,33 @@ TempoMap::gui_dilate_tempo (TempoSection* ts, const framepos_t& frame, const fra
        MetricPositionChanged (); // Emit Signal
 }
 
+double
+TempoMap::exact_beat_at_frame (const framepos_t& frame, const int32_t sub_num)
+{
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       return exact_beat_at_frame_locked (_metrics, frame, sub_num);
+}
+
+double
+TempoMap::exact_beat_at_frame_locked (const Metrics& metrics, const framepos_t& frame, const int32_t sub_num)
+{
+       double beat = beat_at_frame_locked (metrics, frame);
+       if (sub_num > 1) {
+               beat = floor (beat) + (floor (((beat - floor (beat)) * (double) sub_num) + 0.5) / sub_num);
+       } else if (sub_num == 1) {
+               /* snap to beat */
+               beat = floor (beat + 0.5);
+       } else if (sub_num == -1) {
+               /* snap to  bar */
+               Timecode::BBT_Time bbt = bbt_at_beat_locked (metrics, beat);
+               bbt.beats = 1;
+               bbt.ticks = 0;
+               beat = beat_at_bbt_locked (metrics, bbt);
+       }
+       return beat;
+}
+
 framecnt_t
 TempoMap::bbt_duration_at (framepos_t pos, const BBT_Time& bbt, int dir)
 {
@@ -2757,22 +3138,22 @@ TempoMap::round_to_type (framepos_t frame, RoundMode dir, BBTPointType type)
                        /* find bar previous to 'frame' */
                        bbt.beats = 1;
                        bbt.ticks = 0;
-                       return frame_time_locked (_metrics, bbt);
+                       return frame_at_bbt_locked (_metrics, bbt);
 
                } else if (dir > 0) {
                        /* find bar following 'frame' */
                        ++bbt.bars;
                        bbt.beats = 1;
                        bbt.ticks = 0;
-                       return frame_time_locked (_metrics, bbt);
+                       return frame_at_bbt_locked (_metrics, bbt);
                } else {
                        /* true rounding: find nearest bar */
-                       framepos_t raw_ft = frame_time_locked (_metrics, bbt);
+                       framepos_t raw_ft = frame_at_bbt_locked (_metrics, bbt);
                        bbt.beats = 1;
                        bbt.ticks = 0;
-                       framepos_t prev_ft = frame_time_locked (_metrics, bbt);
+                       framepos_t prev_ft = frame_at_bbt_locked (_metrics, bbt);
                        ++bbt.bars;
-                       framepos_t next_ft = frame_time_locked (_metrics, bbt);
+                       framepos_t next_ft = frame_at_bbt_locked (_metrics, bbt);
 
                        if ((raw_ft - prev_ft) > (next_ft - prev_ft) / 2) { 
                                return next_ft;
@@ -2808,33 +3189,39 @@ TempoMap::get_grid (vector<TempoMap::BBTPoint>& points,
        if (cnt < 0.0) {
                cnt = 0.0;
        }
+
+       if (frame_at_beat_locked (_metrics, cnt) >= upper) {
+               return;
+       }
+
        while (pos < upper) {
                pos = frame_at_beat_locked (_metrics, cnt);
-               const TempoSection tempo = tempo_section_at_locked (_metrics, pos);
-               const MeterSection meter = meter_section_at_locked (_metrics, pos);
+               const TempoSection tempo = tempo_section_at_frame_locked (_metrics, pos);
+               const MeterSection meter = meter_section_at_frame_locked (_metrics, pos);
                const BBT_Time bbt = bbt_at_beat_locked (_metrics, cnt);
-               points.push_back (BBTPoint (meter, tempo_at_locked (_metrics, pos), pos, bbt.bars, bbt.beats, tempo.c_func()));
+               points.push_back (BBTPoint (meter, tempo_at_frame_locked (_metrics, pos), pos, bbt.bars, bbt.beats, tempo.c_func()));
                ++cnt;
        }
 }
 
 const TempoSection&
-TempoMap::tempo_section_at (framepos_t frame) const
+TempoMap::tempo_section_at_frame (framepos_t frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       return tempo_section_at_locked (_metrics, frame);
+       return tempo_section_at_frame_locked (_metrics, frame);
 }
 
 const TempoSection&
-TempoMap::tempo_section_at_locked (const Metrics& metrics, framepos_t frame) const
+TempoMap::tempo_section_at_frame_locked (const Metrics& metrics, framepos_t frame) const
 {
-       Metrics::const_iterator i;
        TempoSection* prev = 0;
 
-       for (i = metrics.begin(); i != metrics.end(); ++i) {
-               TempoSection* t;
+       TempoSection* t;
 
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
+
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->active()) {
                                continue;
                        }
@@ -2860,28 +3247,12 @@ TempoMap::tempo_section_at_beat_locked (const Metrics& metrics, const double& be
        TempoSection* prev_t = 0;
        const MeterSection* prev_m = &meter_section_at_beat_locked (metrics, beat);
 
-       for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                       if (prev_t && ((t->pulse() - prev_m->pulse()) * prev_m->note_divisor()) + prev_m->beat() > beat) {
-                               break;
-                       }
-                       prev_t = t;
-               }
-
-       }
-       return *prev_t;
-}
-
-const TempoSection&
-TempoMap::tempo_section_at_pulse_locked (const Metrics& metrics, const double& pulse) const
-{
-       TempoSection* prev_t = 0;
+       TempoSection* t;
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
-               TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                       if (prev_t && t->pulse() > pulse) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
+                       if (prev_t && ((t->pulse() - prev_m->pulse()) * prev_m->note_divisor()) + prev_m->beat() > beat) {
                                break;
                        }
                        prev_t = t;
@@ -2899,77 +3270,45 @@ TempoMap::frames_per_beat_at (const framepos_t& frame, const framecnt_t& sr) con
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
 
-       const TempoSection* ts_at = &tempo_section_at_locked (_metrics, frame);
+       const TempoSection* ts_at = 0;
        const TempoSection* ts_after = 0;
        Metrics::const_iterator i;
+       TempoSection* t;
 
        for (i = _metrics.begin(); i != _metrics.end(); ++i) {
-               TempoSection* t;
 
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
+               if ((*i)->is_tempo()) {
+                       t = static_cast<TempoSection*> (*i);
                        if (!t->active()) {
                                continue;
                        }
-                       if ((*i)->frame() > frame) {
+                       if (ts_at && (*i)->frame() > frame) {
                                ts_after = t;
                                break;
                        }
+                       ts_at = t;
                }
        }
 
        if (ts_after) {
-               return  (60.0 * _frame_rate) / (ts_at->tempo_at_frame (frame, _frame_rate));
+               return  (60.0 * _frame_rate) / (ts_at->tempo_at_frame (frame, _frame_rate) * ts_at->note_type());
        }
        /* must be treated as constant tempo */
        return ts_at->frames_per_beat (_frame_rate);
 }
 
-const Tempo
-TempoMap::tempo_at_locked (const Metrics& metrics, const framepos_t& frame) const
-{
-       TempoSection* prev_t = 0;
-
-       Metrics::const_iterator i;
-
-       for (i = _metrics.begin(); i != _metrics.end(); ++i) {
-               TempoSection* t;
-               if ((t = dynamic_cast<TempoSection*> (*i)) != 0) {
-                       if (!t->active()) {
-                               continue;
-                       }
-                       if ((prev_t) && t->frame() > frame) {
-                               /* t is the section past frame */
-                               const double ret_bpm = prev_t->tempo_at_frame (frame, _frame_rate) * prev_t->note_type();
-                               const Tempo ret_tempo (ret_bpm, prev_t->note_type());
-                               return ret_tempo;
-                       }
-                       prev_t = t;
-               }
-       }
-
-       const double ret = prev_t->beats_per_minute();
-       const Tempo ret_tempo (ret, prev_t->note_type ());
-
-       return ret_tempo;
-}
-
-const Tempo
-TempoMap::tempo_at (const framepos_t& frame) const
-{
-       Glib::Threads::RWLock::ReaderLock lm (lock);
-       return tempo_at_locked (_metrics, frame);
-}
-
 const MeterSection&
-TempoMap::meter_section_at_locked (const Metrics& metrics, framepos_t frame) const
+TempoMap::meter_section_at_frame_locked (const Metrics& metrics, framepos_t frame) const
 {
        Metrics::const_iterator i;
        MeterSection* prev = 0;
 
+       MeterSection* m;
+
        for (i = metrics.begin(); i != metrics.end(); ++i) {
-               MeterSection* m;
 
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
 
                        if (prev && (*i)->frame() > frame) {
                                break;
@@ -2989,10 +3328,10 @@ TempoMap::meter_section_at_locked (const Metrics& metrics, framepos_t frame) con
 
 
 const MeterSection&
-TempoMap::meter_section_at (framepos_t frame) const
+TempoMap::meter_section_at_frame (framepos_t frame) const
 {
        Glib::Threads::RWLock::ReaderLock lm (lock);
-       return meter_section_at_locked (_metrics, frame);
+       return meter_section_at_frame_locked (_metrics, frame);
 }
 
 const MeterSection&
@@ -3002,7 +3341,8 @@ TempoMap::meter_section_at_beat_locked (const Metrics& metrics, const double& be
 
        for (Metrics::const_iterator i = metrics.begin(); i != metrics.end(); ++i) {
                MeterSection* m;
-               if ((m = dynamic_cast<MeterSection*> (*i)) != 0) {
+               if (!(*i)->is_tempo()) {
+                       m = static_cast<MeterSection*> (*i);
                        if (prev_m && m->beat() > beat) {
                                break;
                        }
@@ -3021,7 +3361,7 @@ TempoMap::meter_section_at_beat (double beat) const
 }
 
 const Meter&
-TempoMap::meter_at (framepos_t frame) const
+TempoMap::meter_at_frame (framepos_t frame) const
 {
        TempoMetric m (metric_at (frame));
        return m.meter();
@@ -3131,6 +3471,7 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                                catch (failed_constructor& err){
                                        error << _("Tempo map: could not set new state, restoring old one.") << endmsg;
                                        _metrics = old_metrics;
+                                       old_metrics.clear();
                                        break;
                                }
 
@@ -3144,6 +3485,7 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                                catch (failed_constructor& err) {
                                        error << _("Tempo map: could not set new state, restoring old one.") << endmsg;
                                        _metrics = old_metrics;
+                                       old_metrics.clear();
                                        break;
                                }
                        }
@@ -3195,6 +3537,13 @@ TempoMap::set_state (const XMLNode& node, int /*version*/)
                }
 
                recompute_map (_metrics);
+
+               Metrics::const_iterator d = old_metrics.begin();
+               while (d != old_metrics.end()) {
+                       delete (*d);
+                       ++d;
+               }
+               old_metrics.clear ();
        }
 
        PropertyChanged (PropertyChange ());
@@ -3236,7 +3585,7 @@ TempoMap::n_tempos() const
        int cnt = 0;
 
        for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
-               if (dynamic_cast<const TempoSection*>(*i) != 0) {
+               if ((*i)->is_tempo()) {
                        cnt++;
                }
        }
@@ -3251,7 +3600,7 @@ TempoMap::n_meters() const
        int cnt = 0;
 
        for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
-               if (dynamic_cast<const MeterSection*>(*i) != 0) {
+               if (!(*i)->is_tempo()) {
                        cnt++;
                }
        }
@@ -3345,7 +3694,7 @@ TempoMap::insert_time (framepos_t where, framecnt_t amount)
                                tempo = t;
                                // cerr << "NEW TEMPO, frame = " << (*i)->frame() << " beat = " << (*i)->pulse() <<endl;
                        } else if ((m = dynamic_cast<MeterSection*>(*i)) != 0) {
-                               bbt_time (m->frame(), bbt);
+                               bbt = bbt_at_frame_locked (_metrics, m->frame());
 
                                // cerr << "timestamp @ " << (*i)->frame() << " with " << bbt.bars << "|" << bbt.beats << "|" << bbt.ticks << " => ";
 
@@ -3450,16 +3799,41 @@ TempoMap::remove_time (framepos_t where, framecnt_t amount)
  *  pos can be -ve, if required.
  */
 framepos_t
-TempoMap::framepos_plus_beats (framepos_t pos, Evoral::Beats beats) const
+TempoMap::framepos_plus_beats (framepos_t frame, Evoral::Beats beats) const
 {
-       return frame_at_beat (beat_at_frame (pos) + beats.to_double());
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       const TempoSection& ts = tempo_section_at_frame_locked (_metrics, frame);
+       MeterSection* prev_m = 0;
+       MeterSection* next_m = 0;
+
+       for (Metrics::const_iterator i = _metrics.begin(); i != _metrics.end(); ++i) {
+               if (!(*i)->is_tempo()) {
+                       if (prev_m && (*i)->frame() > frame) {
+                               next_m = static_cast<MeterSection*> (*i);
+                               break;
+                       }
+                       prev_m = static_cast<MeterSection*> (*i);
+               }
+       }
+
+       double pos_beat = prev_m->beat() + (ts.pulse_at_frame (frame, _frame_rate) - prev_m->pulse()) * prev_m->note_divisor();
+
+       /* audio locked meters fake their beat */
+       if (next_m && next_m->beat() < pos_beat) {
+               pos_beat = next_m->beat();
+       }
+
+       return frame_at_beat_locked (_metrics, pos_beat + beats.to_double());
 }
 
 /** Subtract some (fractional) beats from a frame position, and return the result in frames */
 framepos_t
 TempoMap::framepos_minus_beats (framepos_t pos, Evoral::Beats beats) const
 {
-       return frame_at_beat (beat_at_frame (pos) - beats.to_double());
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       return frame_at_beat_locked (_metrics, beat_at_frame_locked (_metrics, pos) - beats.to_double());
 }
 
 /** Add the BBT interval op to pos and return the result */
@@ -3484,7 +3858,7 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
        }
        pos_bbt.bars += op.bars;
 
-       return frame_time_locked (_metrics, pos_bbt);
+       return frame_at_bbt_locked (_metrics, pos_bbt);
 }
 
 /** Count the number of beats that are equivalent to distance when going forward,
@@ -3493,7 +3867,9 @@ TempoMap::framepos_plus_bbt (framepos_t pos, BBT_Time op) const
 Evoral::Beats
 TempoMap::framewalk_to_beats (framepos_t pos, framecnt_t distance) const
 {
-       return Evoral::Beats (beat_at_frame (pos + distance) - beat_at_frame (pos));
+       Glib::Threads::RWLock::ReaderLock lm (lock);
+
+       return Evoral::Beats (beat_at_frame_locked (_metrics, pos + distance) - beat_at_frame_locked (_metrics, pos));
 }
 
 struct bbtcmp {