Initial changes needed for building Mixbus (with MSVC) as version 5
[ardour.git] / libs / ardour / disk_reader.cc
index 951a1aa632e543e7e3370fa33975a706da663d58..375dda70759f0f4345e193223d07eb67b0c04fb5 100644 (file)
 
 */
 
-#include "pbd/i18n.h"
+#include <boost/smart_ptr/scoped_array.hpp>
+
+#include "pbd/enumwriter.h"
+#include "pbd/memento_command.h"
 
+#include "ardour/audioengine.h"
+#include "ardour/audioplaylist.h"
+#include "ardour/audio_buffer.h"
+#include "ardour/butler.h"
 #include "ardour/debug.h"
 #include "ardour/disk_reader.h"
+#include "ardour/midi_ring_buffer.h"
+#include "ardour/midi_playlist.h"
+#include "ardour/midi_track.h"
+#include "ardour/pannable.h"
 #include "ardour/playlist.h"
+#include "ardour/playlist_factory.h"
 #include "ardour/session.h"
+#include "ardour/session_playlists.h"
+
+#include "pbd/i18n.h"
 
 using namespace ARDOUR;
 using namespace PBD;
 using namespace std;
 
-ARDOUR::framecnt_t DiskReader::_chunk_frames = default_chunk_frames ();
+ARDOUR::samplecnt_t DiskReader::_chunk_samples = default_chunk_samples ();
+PBD::Signal0<void> DiskReader::Underrun;
+Sample* DiskReader::_mixdown_buffer = 0;
+gain_t* DiskReader::_gain_buffer = 0;
+samplecnt_t DiskReader::midi_readahead = 4096;
+bool DiskReader::_no_disk_output = false;
 
 DiskReader::DiskReader (Session& s, string const & str, DiskIOProcessor::Flag f)
        : DiskIOProcessor (s, str, f)
-       , _roll_delay (0)
-       , overwrite_frame (0)
-        , overwrite_offset (0)
-        , _pending_overwrite (false)
-        , overwrite_queued (false)
-        , file_frame (0)
-        , playback_sample (0)
+       , overwrite_sample (0)
+       , overwrite_offset (0)
+       , _pending_overwrite (false)
+       , overwrite_queued (false)
+       , _declick_gain (0)
 {
+       file_sample[DataType::AUDIO] = 0;
+       file_sample[DataType::MIDI] = 0;
 }
 
 DiskReader::~DiskReader ()
 {
-       DEBUG_TRACE (DEBUG::Destruction, string_compose ("DiskReader %1 deleted\n", _name));
+       DEBUG_TRACE (DEBUG::Destruction, string_compose ("DiskReader %1 @ %2 deleted\n", _name, this));
+
+       for (uint32_t n = 0; n < DataType::num_types; ++n) {
+               if (_playlists[n]) {
+                       _playlists[n]->release ();
+               }
+       }
+       delete _midi_buf;
+}
+
+void
+DiskReader::ReaderChannelInfo::resize (samplecnt_t bufsize)
+{
+       delete rbuf;
+       /* touch memory to lock it */
+       rbuf = new RingBufferNPT<Sample> (bufsize);
+       memset (rbuf->buffer(), 0, sizeof (Sample) * rbuf->bufsize());
+}
 
-       if (_playlist) {
-               _playlist->release ();
+int
+DiskReader::add_channel_to (boost::shared_ptr<ChannelList> c, uint32_t how_many)
+{
+       while (how_many--) {
+               c->push_back (new ReaderChannelInfo (_session.butler()->audio_diskstream_playback_buffer_size()));
+               DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: new reader channel, write space = %2 read = %3\n",
+                                                           name(),
+                                                           c->back()->rbuf->write_space(),
+                                                           c->back()->rbuf->read_space()));
        }
+
+       return 0;
 }
 
-framecnt_t
-DiskReader::default_chunk_frames()
+void
+DiskReader::allocate_working_buffers()
+{
+       /* with varifill buffer refilling, we compute the read size in bytes (to optimize
+          for disk i/o bandwidth) and then convert back into samples. These buffers
+          need to reflect the maximum size we could use, which is 4MB reads, or 2M samples
+          using 16 bit samples.
+       */
+       _mixdown_buffer       = new Sample[2*1048576];
+       _gain_buffer          = new gain_t[2*1048576];
+}
+
+void
+DiskReader::free_working_buffers()
+{
+       delete [] _mixdown_buffer;
+       delete [] _gain_buffer;
+       _mixdown_buffer       = 0;
+       _gain_buffer          = 0;
+}
+
+samplecnt_t
+DiskReader::default_chunk_samples()
 {
        return 65536;
 }
@@ -60,15 +127,78 @@ DiskReader::default_chunk_frames()
 bool
 DiskReader::set_name (string const & str)
 {
-       if (_name != str) {
-               assert (_playlist);
-               _playlist->set_name (str);
-               SessionObject::set_name(str);
+       string my_name = X_("player:");
+       my_name += str;
+
+       if (_name != my_name) {
+               SessionObject::set_name (my_name);
        }
 
        return true;
 }
 
+XMLNode&
+DiskReader::state ()
+{
+       XMLNode& node (DiskIOProcessor::state ());
+       node.set_property(X_("type"), X_("diskreader"));
+       return node;
+}
+
+int
+DiskReader::set_state (const XMLNode& node, int version)
+{
+       if (DiskIOProcessor::set_state (node, version)) {
+               return -1;
+       }
+
+       return 0;
+}
+
+void
+DiskReader::realtime_handle_transport_stopped ()
+{
+}
+
+void
+DiskReader::realtime_locate ()
+{
+}
+
+float
+DiskReader::buffer_load () const
+{
+       /* Note: for MIDI it's not trivial to differentiate the following two cases:
+
+          1.  The playback buffer is empty because the system has run out of time to fill it.
+          2.  The playback buffer is empty because there is no more data on the playlist.
+
+          If we use a simple buffer load computation, we will report that the MIDI diskstream
+          cannot keep up when #2 happens, when in fact it can.  Since MIDI data rates
+          are so low compared to audio, just use the audio value here.
+       */
+
+       boost::shared_ptr<ChannelList> c = channels.reader();
+
+       if (c->empty ()) {
+               /* no channels, so no buffers, so completely full and ready to playback, sir! */
+               return 1.0;
+       }
+
+       PBD::RingBufferNPT<Sample>* b = c->front()->rbuf;
+       return (float) ((double) b->read_space() / (double) b->bufsize());
+}
+
+void
+DiskReader::adjust_buffering ()
+{
+       boost::shared_ptr<ChannelList> c = channels.reader();
+
+       for (ChannelList::iterator chan = c->begin(); chan != c->end(); ++chan) {
+               (*chan)->resize (_session.butler()->audio_diskstream_playback_buffer_size());
+       }
+}
+
 void
 DiskReader::playlist_changed (const PropertyChange&)
 {
@@ -79,99 +209,1315 @@ void
 DiskReader::playlist_modified ()
 {
        if (!i_am_the_modifier && !overwrite_queued) {
-               // !!!! _session.request_overwrite_buffer (this);
+               _session.request_overwrite_buffer (_route);
+               overwrite_queued = true;
+       }
+}
+
+int
+DiskReader::use_playlist (DataType dt, boost::shared_ptr<Playlist> playlist)
+{
+        bool prior_playlist = false;
+
+        if (_playlists[dt]) {
+               prior_playlist = true;
+        }
+
+        if (DiskIOProcessor::use_playlist (dt, playlist)) {
+               return -1;
+       }
+
+       /* don't do this if we've already asked for it *or* if we are setting up
+          the diskstream for the very first time - the input changed handling will
+          take care of the buffer refill.
+       */
+
+        if (!overwrite_queued && (prior_playlist || _session.loading())) {
+               _session.request_overwrite_buffer (_route);
                overwrite_queued = true;
        }
+
+       return 0;
 }
 
 void
-DiskReader::playlist_deleted (boost::weak_ptr<Playlist> wpl)
+DiskReader::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_sample,
+                 double speed, pframes_t nframes, bool result_required)
 {
-       boost::shared_ptr<Playlist> pl (wpl.lock());
+       uint32_t n;
+       boost::shared_ptr<ChannelList> c = channels.reader();
+       ChannelList::iterator chan;
+       sampleoffset_t disk_samples_to_consume;
+       MonitorState ms = _route->monitoring_state ();
 
-       if (pl == _playlist) {
+       if (_active) {
+               if (!_pending_active) {
+                       _active = false;
+                       return;
+               }
+       } else {
+               if (_pending_active) {
+                       _active = true;
+               } else {
+                       return;
+               }
+       }
 
-               /* this catches an ordering issue with session destruction. playlists
-                  are destroyed before disk readers. we have to invalidate any handles
-                  we have to the playlist.
-               */
+       if ((speed == 0.0) && (ms == MonitoringDisk)) {
+               /* no channels, or stopped. Don't accidentally pass any data
+                * from disk into our outputs (e.g. via interpolation)
+                */
+               return;
+       }
+
+       BufferSet& scratch_bufs (_session.get_scratch_buffers (bufs.count()));
+       const bool still_locating = _session.global_locate_pending();
+
+       if (c->empty()) {
+               /* do nothing with audio */
+               goto midi;
+       }
+
+       assert (speed == -1 || speed == 0 || speed == 1);
+
+       if (speed < 0) {
+               disk_samples_to_consume = -nframes;
+       } else if (speed > 0) {
+               disk_samples_to_consume = nframes;
+       } else {
+               disk_samples_to_consume = 0;
+       }
+
+       if (!result_required || ((ms & MonitoringDisk) == 0) || still_locating || _no_disk_output) {
+
+               /* no need for actual disk data, just advance read pointer and return */
+
+               if (!still_locating || _no_disk_output) {
+                       for (ChannelList::iterator chan = c->begin(); chan != c->end(); ++chan) {
+                               (*chan)->rbuf->increment_read_ptr (disk_samples_to_consume);
+                       }
+               }
+
+               /* if monitoring disk but locating put silence in the buffers */
+
+               if ((_no_disk_output || still_locating) && (ms == MonitoringDisk)) {
+                       bufs.silence (nframes, 0);
+               }
+
+       } else {
+
+               /* we need audio data from disk */
+
+               size_t n_buffers = bufs.count().n_audio();
+               size_t n_chans = c->size();
+               gain_t scaling;
+
+               if (n_chans > n_buffers) {
+                       scaling = ((float) n_buffers)/n_chans;
+               } else {
+                       scaling = 1.0;
+               }
+
+               for (n = 0, chan = c->begin(); chan != c->end(); ++chan, ++n) {
+
+                       ChannelInfo* chaninfo (*chan);
+                       AudioBuffer& output (bufs.get_audio (n%n_buffers));
+                       Sample* disk_signal = 0; /* assignment not really needed but it keeps the compiler quiet and helps track bugs */
+
+                       if (ms & MonitoringInput) {
+                               /* put disk stream in scratch buffer, blend at end */
+                               disk_signal = scratch_bufs.get_audio(n).data ();
+                       } else {
+                               /* no input stream needed, just overwrite buffers */
+                               disk_signal = output.data ();
+                       }
+
+                       if (speed > 0) {
+                               if (start_sample < playback_sample) {
+                                       cerr << owner()->name() << " SS = " << start_sample << " PS = " << playback_sample << endl;
+                                       abort ();
+                               }
+                       } else if (speed < 0) {
+                               if (playback_sample < start_sample) {
+                                       cerr << owner()->name() << " SS = " << start_sample << " PS = " << playback_sample << " REVERSE" << endl;
+                                       abort ();
+                               }
+                       }
+
+                       if ((speed > 0) && (start_sample != playback_sample)) {
+                               cerr << owner()->name() << " playback not aligned, jump ahead " << (start_sample - playback_sample) << endl;
+
+                               if (can_internal_playback_seek (start_sample - playback_sample)) {
+                                       internal_playback_seek (start_sample - playback_sample);
+                               } else {
+                                       cerr << owner()->name() << " playback not possible: ss = " << start_sample << " ps = " << playback_sample << endl;
+                                       goto midi;
+                               }
+                       }
+
+                       chaninfo->rbuf->get_read_vector (&(*chan)->rw_vector);
+
+                       if (disk_samples_to_consume <= (samplecnt_t) chaninfo->rw_vector.len[0]) {
+
+                               if (speed != 0.0) {
+                                       memcpy (disk_signal, chaninfo->rw_vector.buf[0], sizeof (Sample) * disk_samples_to_consume);
+                               }
+
+                       } else {
+
+                               const samplecnt_t total = chaninfo->rw_vector.len[0] + chaninfo->rw_vector.len[1];
+
+                               if (disk_samples_to_consume <= total) {
+
+                                               if (speed != 0.0) {
+                                                       memcpy (disk_signal,
+                                                       chaninfo->rw_vector.buf[0],
+                                                       chaninfo->rw_vector.len[0] * sizeof (Sample));
+                                                       memcpy (disk_signal + chaninfo->rw_vector.len[0],
+                                                       chaninfo->rw_vector.buf[1],
+                                                       (disk_samples_to_consume - chaninfo->rw_vector.len[0]) * sizeof (Sample));
+                                       }
+
+                               } else {
+
+                                       cerr << _name << " Need " << disk_samples_to_consume << " total = " << total << endl;
+                                       cerr << "underrun for " << _name << endl;
+                                       DEBUG_TRACE (DEBUG::Butler, string_compose ("%1 underrun in %2, total space = %3\n",
+                                                                                   DEBUG_THREAD_SELF, name(), total));
+                                       Underrun ();
+                                       return;
+
+                               }
+                       }
+
+                       if (scaling != 1.0f && speed != 0.0) {
+                               apply_gain_to_buffer (disk_signal, disk_samples_to_consume, scaling);
+                       }
+
+                       chaninfo->rbuf->increment_read_ptr (disk_samples_to_consume);
+
+                       if (ms & MonitoringInput) {
+                               /* mix the disk signal into the input signal (already in bufs) */
+                               mix_buffers_no_gain (output.data(), disk_signal, disk_samples_to_consume);
+                       }
+               }
+       }
+
+       /* MIDI data handling */
+
+  midi:
+       if (/*!_session.declick_out_pending() && */ bufs.count().n_midi()) {
+               MidiBuffer* dst;
+
+               if (_no_disk_output) {
+                       dst = &scratch_bufs.get_midi(0);
+               } else {
+                       dst = &bufs.get_midi (0);
+               }
+
+               if ((ms & MonitoringDisk) && !still_locating) {
+                       get_midi_playback (*dst, start_sample, end_sample, ms, scratch_bufs, speed, disk_samples_to_consume);
+               }
+       }
+
+       if (!still_locating) {
+
+               bool butler_required = false;
+
+               if (speed < 0.0) {
+                       playback_sample -= disk_samples_to_consume;
+               } else {
+                       playback_sample += disk_samples_to_consume;
+               }
+
+               if (_playlists[DataType::AUDIO]) {
+                       if (!c->empty()) {
+                               if (_slaved) {
+                                       if (c->front()->rbuf->write_space() >= c->front()->rbuf->bufsize() / 2) {
+                                               DEBUG_TRACE (DEBUG::Butler, string_compose ("%1: slaved, write space = %2 of %3\n", name(), c->front()->rbuf->write_space(), c->front()->rbuf->bufsize()));
+                                               butler_required = true;
+                                       }
+                               } else {
+                                       if ((samplecnt_t) c->front()->rbuf->write_space() >= _chunk_samples) {
+                                               DEBUG_TRACE (DEBUG::Butler, string_compose ("%1: write space = %2 of %3\n", name(), c->front()->rbuf->write_space(),
+                                                                                           _chunk_samples));
+                                               butler_required = true;
+                                       }
+                               }
+                       }
+               }
+
+               if (_playlists[DataType::MIDI]) {
+                       /* MIDI butler needed part */
+
+                       uint32_t samples_read = g_atomic_int_get(const_cast<gint*>(&_samples_read_from_ringbuffer));
+                       uint32_t samples_written = g_atomic_int_get(const_cast<gint*>(&_samples_written_to_ringbuffer));
+
+                       /*
+                         cerr << name() << " MDS written: " << samples_written << " - read: " << samples_read <<
+                         " = " << samples_written - samples_read
+                         << " + " << disk_samples_to_consume << " < " << midi_readahead << " = " << need_butler << ")" << endl;
+                       */
+
+                       /* samples_read will generally be less than samples_written, but
+                        * immediately after an overwrite, we can end up having read some data
+                        * before we've written any. we don't need to trip an assert() on this,
+                        * but we do need to check so that the decision on whether or not we
+                        * need the butler is done correctly.
+                        */
+
+                       /* furthermore..
+                        *
+                        * Doing heavy GUI operations[1] can stall also the butler.
+                        * The RT-thread meanwhile will happily continue and
+                        * â€˜samples_read’ (from buffer to output) will become larger
+                        * than â€˜samples_written’ (from disk to buffer).
+                        *
+                        * The disk-stream is now behind..
+                        *
+                        * In those cases the butler needs to be summed to refill the buffer (done now)
+                        * AND we need to skip (samples_read - samples_written). ie remove old events
+                        * before playback_sample from the rinbuffer.
+                        *
+                        * [1] one way to do so is described at #6170.
+                        * For me just popping up the context-menu on a MIDI-track header
+                        * of a track with a large (think beethoven :) midi-region also did the
+                        * trick. The playhead stalls for 2 or 3 sec, until the context-menu shows.
+                        *
+                        * In both cases the root cause is that redrawing MIDI regions on the GUI is still very slow
+                        * and can stall
+                        */
+                       if (samples_read <= samples_written) {
+                               if ((samples_written - samples_read) + disk_samples_to_consume < midi_readahead) {
+                                       butler_required = true;
+                               }
+                       } else {
+                               butler_required = true;
+                       }
 
-               if (_playlist) {
-                       _playlist.reset ();
                }
+
+               _need_butler = butler_required;
+       }
+
+       // DEBUG_TRACE (DEBUG::Butler, string_compose ("%1 reader run, needs butler = %2\n", name(), _need_butler));
+}
+
+void
+DiskReader::set_pending_overwrite (bool yn)
+{
+       /* called from audio thread, so we can use the read ptr and playback sample as we wish */
+
+       _pending_overwrite = yn;
+
+       overwrite_sample = playback_sample;
+
+       boost::shared_ptr<ChannelList> c = channels.reader ();
+       if (!c->empty ()) {
+               overwrite_offset = c->front()->rbuf->get_read_ptr();
        }
 }
 
 int
-DiskReader::use_playlist (boost::shared_ptr<Playlist> playlist)
+DiskReader::overwrite_existing_buffers ()
 {
-        if (!playlist) {
-                return 0;
-        }
+       int ret = -1;
 
-        bool prior_playlist = false;
+       boost::shared_ptr<ChannelList> c = channels.reader();
 
-       {
-               Glib::Threads::Mutex::Lock lm (state_lock);
+       overwrite_queued = false;
 
-               if (playlist == _playlist) {
-                       return 0;
-               }
+       DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1 overwriting existing buffers at %2\n", overwrite_sample));
 
-               playlist_connections.drop_connections ();
+       if (!c->empty ()) {
 
-               if (_playlist) {
-                       _playlist->release();
-                        prior_playlist = true;
+               /* AUDIO */
+
+               const bool reversed = _session.transport_speed() < 0.0f;
+
+               /* assume all are the same size */
+               samplecnt_t size = c->front()->rbuf->bufsize();
+
+               boost::scoped_array<Sample> mixdown_buffer (new Sample[size]);
+               boost::scoped_array<float> gain_buffer (new float[size]);
+
+               /* reduce size so that we can fill the buffer correctly (ringbuffers
+                  can only handle size-1, otherwise they appear to be empty)
+               */
+               size--;
+
+               uint32_t n=0;
+               samplepos_t start;
+
+               for (ChannelList::iterator chan = c->begin(); chan != c->end(); ++chan, ++n) {
+
+                       start = overwrite_sample;
+                       samplecnt_t cnt = size;
+
+                       /* to fill the buffer without resetting the playback sample, we need to
+                          do it one or two chunks (normally two).
+
+                          |----------------------------------------------------------------------|
+
+                          ^
+                          overwrite_offset
+                          |<- second chunk->||<----------------- first chunk ------------------>|
+
+                       */
+
+                       samplecnt_t to_read = size - overwrite_offset;
+
+                       if (audio_read ((*chan)->rbuf->buffer() + overwrite_offset, mixdown_buffer.get(), gain_buffer.get(), start, to_read, n, reversed)) {
+                               error << string_compose(_("DiskReader %1: when refilling, cannot read %2 from playlist at sample %3"),
+                                                       id(), size, playback_sample) << endmsg;
+                               goto midi;
+                       }
+
+                       if (cnt > to_read) {
+
+                               cnt -= to_read;
+
+                               if (audio_read ((*chan)->rbuf->buffer(), mixdown_buffer.get(), gain_buffer.get(), start, cnt, n, reversed)) {
+                                       error << string_compose(_("DiskReader %1: when refilling, cannot read %2 from playlist at sample %3"),
+                                                               id(), size, playback_sample) << endmsg;
+                                       goto midi;
+                               }
+                       }
                }
 
-               _playlist = playlist;
-               _playlist->use();
+               ret = 0;
 
-               _playlist->ContentsChanged.connect_same_thread (playlist_connections, boost::bind (&DiskReader::playlist_modified, this));
-               _playlist->LayeringChanged.connect_same_thread (playlist_connections, boost::bind (&DiskReader::playlist_modified, this));
-               _playlist->DropReferences.connect_same_thread (playlist_connections, boost::bind (&DiskReader::playlist_deleted, this, boost::weak_ptr<Playlist>(_playlist)));
-               _playlist->RangesMoved.connect_same_thread (playlist_connections, boost::bind (&DiskReader::playlist_ranges_moved, this, _1, _2));
        }
 
-       /* don't do this if we've already asked for it *or* if we are setting up
-          the diskstream for the very first time - the input changed handling will
-          take care of the buffer refill.
-       */
+  midi:
 
-       if (!overwrite_queued && prior_playlist) {
-               // !!! _session.request_overwrite_buffer (this);
-               overwrite_queued = true;
+       if (_midi_buf && _playlists[DataType::MIDI]) {
+
+               /* Clear the playback buffer contents.  This is safe as long as the butler
+                  thread is suspended, which it should be.
+               */
+               _midi_buf->reset ();
+               _midi_buf->reset_tracker ();
+
+               g_atomic_int_set (&_samples_read_from_ringbuffer, 0);
+               g_atomic_int_set (&_samples_written_to_ringbuffer, 0);
+
+               /* Resolve all currently active notes in the playlist.  This is more
+                  aggressive than it needs to be: ideally we would only resolve what is
+                  absolutely necessary, but this seems difficult and/or impossible without
+                  having the old data or knowing what change caused the overwrite.
+               */
+               midi_playlist()->resolve_note_trackers (*_midi_buf, overwrite_sample);
+
+               midi_read (overwrite_sample, _chunk_samples, false);
+               file_sample[DataType::MIDI] = overwrite_sample; // overwrite_sample was adjusted by ::midi_read() to the new position
+       }
+
+       _pending_overwrite = false;
+
+       return ret;
+}
+
+int
+DiskReader::seek (samplepos_t sample, bool complete_refill)
+{
+       uint32_t n;
+       int ret = -1;
+       ChannelList::iterator chan;
+       boost::shared_ptr<ChannelList> c = channels.reader();
+
+       //sample = std::max ((samplecnt_t)0, sample -_session.worst_output_latency ());
+
+       for (n = 0, chan = c->begin(); chan != c->end(); ++chan, ++n) {
+               (*chan)->rbuf->reset ();
+       }
+
+       if (g_atomic_int_get (&_samples_read_from_ringbuffer) == 0) {
+               /* we haven't read anything since the last seek,
+                  so flush all note trackers to prevent
+                  wierdness
+               */
+               reset_tracker ();
+       }
+
+       _midi_buf->reset();
+       g_atomic_int_set(&_samples_read_from_ringbuffer, 0);
+       g_atomic_int_set(&_samples_written_to_ringbuffer, 0);
+
+       playback_sample = sample;
+       file_sample[DataType::AUDIO] = sample;
+       file_sample[DataType::MIDI] = sample;
+
+       if (complete_refill) {
+               /* call _do_refill() to refill the entire buffer, using
+                  the largest reads possible.
+               */
+               while ((ret = do_refill_with_alloc (false)) > 0) ;
+       } else {
+               /* call _do_refill() to refill just one chunk, and then
+                  return.
+               */
+               ret = do_refill_with_alloc (true);
+       }
+
+
+       return ret;
+}
+
+int
+DiskReader::can_internal_playback_seek (samplecnt_t distance)
+{
+       /* 1. Audio */
+
+       ChannelList::iterator chan;
+       boost::shared_ptr<ChannelList> c = channels.reader();
+
+       for (chan = c->begin(); chan != c->end(); ++chan) {
+               if ((*chan)->rbuf->read_space() < (size_t) distance) {
+                       return false;
+               }
+       }
+
+       /* 2. MIDI */
+
+       uint32_t samples_read    = g_atomic_int_get(&_samples_read_from_ringbuffer);
+       uint32_t samples_written = g_atomic_int_get(&_samples_written_to_ringbuffer);
+
+       return ((samples_written - samples_read) < distance);
+}
+
+int
+DiskReader::internal_playback_seek (samplecnt_t distance)
+{
+       ChannelList::iterator chan;
+       boost::shared_ptr<ChannelList> c = channels.reader();
+
+       for (chan = c->begin(); chan != c->end(); ++chan) {
+               (*chan)->rbuf->increment_read_ptr (::llabs(distance));
        }
 
-       PlaylistChanged (); /* EMIT SIGNAL */
-       _session.set_dirty ();
+       playback_sample += distance;
 
        return 0;
 }
 
-void
-DiskReader::set_roll_delay (ARDOUR::framecnt_t nframes)
+static
+void swap_by_ptr (Sample *first, Sample *last)
 {
-       _roll_delay = nframes;
+       while (first < last) {
+               Sample tmp = *first;
+               *first++ = *last;
+               *last-- = tmp;
+       }
 }
 
+/** Read some data for 1 channel from our playlist into a buffer.
+ *  @param buf Buffer to write to.
+ *  @param start Session sample to start reading from; updated to where we end up
+ *         after the read.
+ *  @param cnt Count of samples to read.
+ *  @param reversed true if we are running backwards, otherwise false.
+ */
 int
-DiskReader::set_state (const XMLNode& node, int version)
+DiskReader::audio_read (Sample* buf, Sample* mixdown_buffer, float* gain_buffer,
+                        samplepos_t& start, samplecnt_t cnt,
+                        int channel, bool reversed)
 {
-       XMLProperty const * prop;
+       samplecnt_t this_read = 0;
+       bool reloop = false;
+       samplepos_t loop_end = 0;
+       samplepos_t loop_start = 0;
+       samplecnt_t offset = 0;
+       Location *loc = 0;
 
-       if (DiskIOProcessor::set_state (node, version)) {
-               return -1;
+       if (!_playlists[DataType::AUDIO]) {
+               memset (buf, 0, sizeof (Sample) * cnt);
+               return 0;
        }
 
-       if ((prop = node.property ("playlist")) == 0) {
-               return -1;
+       /* XXX we don't currently play loops in reverse. not sure why */
+
+       if (!reversed) {
+
+               samplecnt_t loop_length = 0;
+
+               /* Make the use of a Location atomic for this read operation.
+
+                  Note: Locations don't get deleted, so all we care about
+                  when I say "atomic" is that we are always pointing to
+                  the same one and using a start/length values obtained
+                  just once.
+               */
+
+               if ((loc = _loop_location) != 0) {
+                       loop_start = loc->start();
+                       loop_end = loc->end();
+                       loop_length = loop_end - loop_start;
+               }
+
+               /* if we are looping, ensure that the first sample we read is at the correct
+                  position within the loop.
+               */
+
+               if (loc && start >= loop_end) {
+                       start = loop_start + ((start - loop_start) % loop_length);
+               }
+
        }
 
-       if (find_and_use_playlist (prop->value())) {
-               return -1;
+       if (reversed) {
+               start -= cnt;
        }
 
-       return 0;
+       /* We need this while loop in case we hit a loop boundary, in which case our read from
+          the playlist must be split into more than one section.
+       */
+
+       while (cnt) {
+
+               /* take any loop into account. we can't read past the end of the loop. */
+
+               if (loc && (loop_end - start < cnt)) {
+                       this_read = loop_end - start;
+                       reloop = true;
+               } else {
+                       reloop = false;
+                       this_read = cnt;
+               }
+
+               if (this_read == 0) {
+                       break;
+               }
+
+               this_read = min(cnt,this_read);
+
+               if (audio_playlist()->read (buf+offset, mixdown_buffer, gain_buffer, start, this_read, channel) != this_read) {
+                       error << string_compose(_("DiskReader %1: cannot read %2 from playlist at sample %3"), id(), this_read,
+                                        start) << endmsg;
+                       return -1;
+               }
+
+               if (reversed) {
+
+                       swap_by_ptr (buf, buf + this_read - 1);
+
+               } else {
+
+                       /* if we read to the end of the loop, go back to the beginning */
+
+                       if (reloop) {
+                               start = loop_start;
+                       } else {
+                               start += this_read;
+                       }
+               }
+
+               cnt -= this_read;
+               offset += this_read;
+       }
+
+       return 0;
+}
+
+int
+DiskReader::_do_refill_with_alloc (bool partial_fill)
+{
+       /* We limit disk reads to at most 4MB chunks, which with floating point
+          samples would be 1M samples. But we might use 16 or 14 bit samples,
+          in which case 4MB is more samples than that. Therefore size this for
+          the smallest sample value .. 4MB = 2M samples (16 bit).
+       */
+
+       {
+               boost::scoped_array<Sample> mix_buf (new Sample[2*1048576]);
+               boost::scoped_array<float>  gain_buf (new float[2*1048576]);
+
+               int ret = refill_audio (mix_buf.get(), gain_buf.get(), (partial_fill ? _chunk_samples : 0));
+
+               if (ret) {
+                       return ret;
+               }
+       }
+
+       return refill_midi ();
+}
+
+int
+DiskReader::refill (Sample* mixdown_buffer, float* gain_buffer, samplecnt_t fill_level)
+{
+       int ret = refill_audio (mixdown_buffer, gain_buffer, fill_level);
+
+       if (ret) {
+               return ret;
+       }
+
+       return refill_midi ();
+}
+
+
+/** Get some more data from disk and put it in our channels' bufs,
+ *  if there is suitable space in them.
+ *
+ * If fill_level is non-zero, then we will refill the buffer so that there is
+ * still at least fill_level samples of space left to be filled. This is used
+ * after locates so that we do not need to wait to fill the entire buffer.
+ *
+ */
+
+int
+DiskReader::refill_audio (Sample* mixdown_buffer, float* gain_buffer, samplecnt_t fill_level)
+{
+       /* do not read from disk while session is marked as Loading, to avoid
+          useless redundant I/O.
+       */
+
+       if (_session.loading()) {
+               return 0;
+       }
+
+       int32_t ret = 0;
+       samplecnt_t to_read;
+       RingBufferNPT<Sample>::rw_vector vector;
+       bool const reversed = _session.transport_speed() < 0.0f;
+       samplecnt_t total_space;
+       samplecnt_t zero_fill;
+       uint32_t chan_n;
+       ChannelList::iterator i;
+       boost::shared_ptr<ChannelList> c = channels.reader();
+       samplecnt_t ts;
+
+       if (c->empty()) {
+               return 0;
+       }
+
+       assert(mixdown_buffer);
+       assert(gain_buffer);
+
+       vector.buf[0] = 0;
+       vector.len[0] = 0;
+       vector.buf[1] = 0;
+       vector.len[1] = 0;
+
+       c->front()->rbuf->get_write_vector (&vector);
+
+       if ((total_space = vector.len[0] + vector.len[1]) == 0) {
+               DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: no space to refill\n", name()));
+               /* nowhere to write to */
+               return 0;
+       }
+
+       if (fill_level) {
+               if (fill_level < total_space) {
+                       total_space -= fill_level;
+               } else {
+                       /* we can't do anything with it */
+                       fill_level = 0;
+               }
+       }
+
+       /* if we're running close to normal speed and there isn't enough
+          space to do disk_read_chunk_samples of I/O, then don't bother.
+
+          at higher speeds, just do it because the sync between butler
+          and audio thread may not be good enough.
+
+          Note: it is a design assumption that disk_read_chunk_samples is smaller
+          than the playback buffer size, so this check should never trip when
+          the playback buffer is empty.
+       */
+
+       DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: space to refill %2 vs. chunk %3 (speed = %4)\n", name(), total_space, _chunk_samples, _session.transport_speed()));
+       if ((total_space < _chunk_samples) && fabs (_session.transport_speed()) < 2.0f) {
+               return 0;
+       }
+
+       /* when slaved, don't try to get too close to the read pointer. this
+          leaves space for the buffer reversal to have something useful to
+          work with.
+       */
+
+       if (_slaved && total_space < (samplecnt_t) (c->front()->rbuf->bufsize() / 2)) {
+               DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: not enough to refill while slaved\n", this));
+               return 0;
+       }
+
+       samplepos_t ffa = file_sample[DataType::AUDIO];
+
+       if (reversed) {
+
+               if (ffa == 0) {
+
+                       /* at start: nothing to do but fill with silence */
+
+                       for (chan_n = 0, i = c->begin(); i != c->end(); ++i, ++chan_n) {
+
+                               ChannelInfo* chan (*i);
+                               chan->rbuf->get_write_vector (&vector);
+                               memset (vector.buf[0], 0, sizeof(Sample) * vector.len[0]);
+                               if (vector.len[1]) {
+                                       memset (vector.buf[1], 0, sizeof(Sample) * vector.len[1]);
+                               }
+                               chan->rbuf->increment_write_ptr (vector.len[0] + vector.len[1]);
+                       }
+                       return 0;
+               }
+
+               if (ffa < total_space) {
+
+                       /* too close to the start: read what we can,
+                          and then zero fill the rest
+                       */
+
+                       zero_fill = total_space - ffa;
+                       total_space = ffa;
+
+               } else {
+
+                       zero_fill = 0;
+               }
+
+       } else {
+
+               if (ffa == max_samplepos) {
+
+                       /* at end: nothing to do but fill with silence */
+
+                       for (chan_n = 0, i = c->begin(); i != c->end(); ++i, ++chan_n) {
+
+                               ChannelInfo* chan (*i);
+                               chan->rbuf->get_write_vector (&vector);
+                               memset (vector.buf[0], 0, sizeof(Sample) * vector.len[0]);
+                               if (vector.len[1]) {
+                                       memset (vector.buf[1], 0, sizeof(Sample) * vector.len[1]);
+                               }
+                               chan->rbuf->increment_write_ptr (vector.len[0] + vector.len[1]);
+                       }
+                       return 0;
+               }
+
+               if (ffa > max_samplepos - total_space) {
+
+                       /* to close to the end: read what we can, and zero fill the rest */
+
+                       zero_fill = total_space - (max_samplepos - ffa);
+                       total_space = max_samplepos - ffa;
+
+               } else {
+                       zero_fill = 0;
+               }
+       }
+
+       samplepos_t file_sample_tmp = 0;
+
+       /* total_space is in samples. We want to optimize read sizes in various sizes using bytes */
+
+       const size_t bits_per_sample = format_data_width (_session.config.get_native_file_data_format());
+       size_t total_bytes = total_space * bits_per_sample / 8;
+
+       /* chunk size range is 256kB to 4MB. Bigger is faster in terms of MB/sec, but bigger chunk size always takes longer
+        */
+       size_t byte_size_for_read = max ((size_t) (256 * 1024), min ((size_t) (4 * 1048576), total_bytes));
+
+       /* find nearest (lower) multiple of 16384 */
+
+       byte_size_for_read = (byte_size_for_read / 16384) * 16384;
+
+       /* now back to samples */
+
+       samplecnt_t samples_to_read = byte_size_for_read / (bits_per_sample / 8);
+
+       DEBUG_TRACE (DEBUG::DiskIO, string_compose ("%1: will refill %2 channels with %3 samples\n", name(), c->size(), total_space));
+
+       // uint64_t before = g_get_monotonic_time ();
+       // uint64_t elapsed;
+
+       for (chan_n = 0, i = c->begin(); i != c->end(); ++i, ++chan_n) {
+
+               ChannelInfo* chan (*i);
+               Sample* buf1;
+               Sample* buf2;
+               samplecnt_t len1, len2;
+
+               chan->rbuf->get_write_vector (&vector);
+
+               if ((samplecnt_t) vector.len[0] > samples_to_read) {
+
+                       /* we're not going to fill the first chunk, so certainly do not bother with the
+                          other part. it won't be connected with the part we do fill, as in:
+
+                          .... => writable space
+                          ++++ => readable space
+                          ^^^^ => 1 x disk_read_chunk_samples that would be filled
+
+                          |......|+++++++++++++|...............................|
+                          buf1                buf0
+                                               ^^^^^^^^^^^^^^^
+
+
+                          So, just pretend that the buf1 part isn't there.
+
+                       */
+
+                       vector.buf[1] = 0;
+                       vector.len[1] = 0;
+
+               }
+
+               ts = total_space;
+               file_sample_tmp = ffa;
+
+               buf1 = vector.buf[0];
+               len1 = vector.len[0];
+               buf2 = vector.buf[1];
+               len2 = vector.len[1];
+
+               to_read = min (ts, len1);
+               to_read = min (to_read, (samplecnt_t) samples_to_read);
+
+               assert (to_read >= 0);
+
+               if (to_read) {
+
+                       if (audio_read (buf1, mixdown_buffer, gain_buffer, file_sample_tmp, to_read, chan_n, reversed)) {
+                               ret = -1;
+                               goto out;
+                       }
+                       chan->rbuf->increment_write_ptr (to_read);
+                       ts -= to_read;
+               }
+
+               to_read = min (ts, len2);
+
+               if (to_read) {
+
+                       /* we read all of vector.len[0], but it wasn't the
+                          entire samples_to_read of data, so read some or
+                          all of vector.len[1] as well.
+                       */
+
+                       if (audio_read (buf2, mixdown_buffer, gain_buffer, file_sample_tmp, to_read, chan_n, reversed)) {
+                               ret = -1;
+                               goto out;
+                       }
+
+                       chan->rbuf->increment_write_ptr (to_read);
+               }
+
+               if (zero_fill) {
+                       /* XXX: do something */
+               }
+
+       }
+
+       // elapsed = g_get_monotonic_time () - before;
+       // cerr << '\t' << name() << ": bandwidth = " << (byte_size_for_read / 1048576.0) / (elapsed/1000000.0) << "MB/sec\n";
+
+       file_sample[DataType::AUDIO] = file_sample_tmp;
+       assert (file_sample[DataType::AUDIO] >= 0);
+
+       ret = ((total_space - samples_to_read) > _chunk_samples);
+
+       c->front()->rbuf->get_write_vector (&vector);
+
+  out:
+       return ret;
+}
+
+void
+DiskReader::playlist_ranges_moved (list< Evoral::RangeMove<samplepos_t> > const & movements_samples, bool from_undo)
+{
+       /* If we're coming from an undo, it will have handled
+          automation undo (it must, since automation-follows-regions
+          can lose automation data).  Hence we can do nothing here.
+       */
+
+       if (from_undo) {
+               return;
+       }
+
+       if (!_route || Config->get_automation_follows_regions () == false) {
+               return;
+       }
+
+       list< Evoral::RangeMove<double> > movements;
+
+       for (list< Evoral::RangeMove<samplepos_t> >::const_iterator i = movements_samples.begin();
+            i != movements_samples.end();
+            ++i) {
+
+               movements.push_back(Evoral::RangeMove<double>(i->from, i->length, i->to));
+       }
+
+       /* move panner automation */
+       boost::shared_ptr<Pannable> pannable = _route->pannable();
+        Evoral::ControlSet::Controls& c (pannable->controls());
+
+        for (Evoral::ControlSet::Controls::iterator ci = c.begin(); ci != c.end(); ++ci) {
+                boost::shared_ptr<AutomationControl> ac = boost::dynamic_pointer_cast<AutomationControl>(ci->second);
+                if (!ac) {
+                        continue;
+                }
+                boost::shared_ptr<AutomationList> alist = ac->alist();
+               if (!alist->size()) {
+                       continue;
+               }
+                XMLNode & before = alist->get_state ();
+                bool const things_moved = alist->move_ranges (movements);
+                if (things_moved) {
+                        _session.add_command (new MementoCommand<AutomationList> (
+                                                      *alist.get(), &before, &alist->get_state ()));
+                }
+        }
+       /* move processor automation */
+        _route->foreach_processor (boost::bind (&DiskReader::move_processor_automation, this, _1, movements_samples));
+}
+
+void
+DiskReader::move_processor_automation (boost::weak_ptr<Processor> p, list< Evoral::RangeMove<samplepos_t> > const & movements_samples)
+{
+       boost::shared_ptr<Processor> processor (p.lock ());
+       if (!processor) {
+               return;
+       }
+
+       list< Evoral::RangeMove<double> > movements;
+       for (list< Evoral::RangeMove<samplepos_t> >::const_iterator i = movements_samples.begin(); i != movements_samples.end(); ++i) {
+               movements.push_back(Evoral::RangeMove<double>(i->from, i->length, i->to));
+       }
+
+       set<Evoral::Parameter> const a = processor->what_can_be_automated ();
+
+       for (set<Evoral::Parameter>::const_iterator i = a.begin (); i != a.end (); ++i) {
+               boost::shared_ptr<AutomationList> al = processor->automation_control(*i)->alist();
+               if (!al->size()) {
+                       continue;
+               }
+               XMLNode & before = al->get_state ();
+               bool const things_moved = al->move_ranges (movements);
+               if (things_moved) {
+                       _session.add_command (
+                               new MementoCommand<AutomationList> (
+                                       *al.get(), &before, &al->get_state ()
+                                       )
+                               );
+               }
+       }
+}
+
+void
+DiskReader::reset_tracker ()
+{
+       _midi_buf->reset_tracker ();
+
+       boost::shared_ptr<MidiPlaylist> mp (midi_playlist());
+
+       if (mp) {
+               mp->reset_note_trackers ();
+       }
+}
+
+void
+DiskReader::resolve_tracker (Evoral::EventSink<samplepos_t>& buffer, samplepos_t time)
+{
+       _midi_buf->resolve_tracker(buffer, time);
+
+       boost::shared_ptr<MidiPlaylist> mp (midi_playlist());
+
+       if (mp) {
+               mp->reset_note_trackers ();
+       }
+}
+
+/** Writes playback events from playback_sample for nframes to dst, translating time stamps
+ *  so that an event at playback_sample has time = 0
+ */
+void
+DiskReader::get_midi_playback (MidiBuffer& dst, samplepos_t start_sample, samplepos_t end_sample, MonitorState ms, BufferSet& scratch_bufs, double speed, samplecnt_t disk_samples_to_consume)
+{
+       MidiBuffer* target;
+       samplepos_t nframes = end_sample - start_sample;
+
+       if ((ms & MonitoringInput) == 0) {
+               /* Route::process_output_buffers() clears the buffer as-needed */
+               target = &dst;
+       } else {
+               target = &scratch_bufs.get_midi (0);
+       }
+
+       if (ms & MonitoringDisk) {
+               /* disk data needed */
+
+               Location* loc = _loop_location;
+
+               DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose (
+                                    "%1 MDS pre-read read %8 offset = %9 @ %4..%5 from %2 write to %3, LOOPED ? %6 .. %7\n", _name,
+                                    _midi_buf->get_read_ptr(), _midi_buf->get_write_ptr(), start_sample, end_sample,
+                                    (loc ? loc->start() : -1), (loc ? loc->end() : -1), nframes, Port::port_offset()));
+
+               //cerr << "======== PRE ========\n";
+               //_midi_buf->dump (cerr);
+               //cerr << "----------------\n";
+
+               size_t events_read = 0;
+
+               if (loc) {
+                       samplepos_t effective_start;
+
+                       Evoral::Range<samplepos_t> loop_range (loc->start(), loc->end() - 1);
+                       effective_start = loop_range.squish (start_sample);
+
+                       DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("looped, effective start adjusted to %1\n", effective_start));
+
+                       if (effective_start == loc->start()) {
+                               /* We need to turn off notes that may extend
+                                  beyond the loop end.
+                               */
+
+                               _midi_buf->resolve_tracker (*target, 0);
+                       }
+
+                       /* for split-cycles we need to offset the events */
+
+                       if (loc->end() >= effective_start && loc->end() < effective_start + nframes) {
+
+                               /* end of loop is within the range we are reading, so
+                                  split the read in two, and lie about the location
+                                  for the 2nd read
+                               */
+
+                               samplecnt_t first, second;
+
+                               first = loc->end() - effective_start;
+                               second = nframes - first;
+
+                               DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("loop read for eff %1 end %2: %3 and %4, cycle offset %5\n",
+                                                                                     effective_start, loc->end(), first, second));
+
+                               if (first) {
+                                       DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("loop read #1, from %1 for %2\n",
+                                                                                             effective_start, first));
+                                       events_read = _midi_buf->read (*target, effective_start, first);
+                               }
+
+                               if (second) {
+                                       DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("loop read #2, from %1 for %2\n",
+                                                                                             loc->start(), second));
+                                       events_read += _midi_buf->read (*target, loc->start(), second);
+                               }
+
+                       } else {
+                               DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("loop read #3, adjusted start as %1 for %2\n",
+                                                                                     effective_start, nframes));
+                               events_read = _midi_buf->read (*target, effective_start, effective_start + nframes);
+                       }
+               } else {
+                       const size_t n_skipped = _midi_buf->skip_to (start_sample);
+                       if (n_skipped > 0) {
+                               warning << string_compose(_("MidiDiskstream %1: skipped %2 events, possible underflow"), id(), n_skipped) << endmsg;
+                       }
+                       DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("playback buffer read, from %1 to %2 (%3)", start_sample, end_sample, nframes));
+                       events_read = _midi_buf->read (*target, start_sample, end_sample, Port::port_offset ());
+               }
+
+               DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose (
+                                    "%1 MDS events read %2 range %3 .. %4 rspace %5 wspace %6 r@%7 w@%8\n",
+                                    _name, events_read, playback_sample, playback_sample + nframes,
+                                    _midi_buf->read_space(), _midi_buf->write_space(),
+                                    _midi_buf->get_read_ptr(), _midi_buf->get_write_ptr()));
+       }
+
+       g_atomic_int_add (&_samples_read_from_ringbuffer, nframes);
+
+       /* vari-speed */
+       if (speed != 0.0 && fabsf (speed) != 1.0f) {
+               for (MidiBuffer::iterator i = target->begin(); i != target->end(); ++i) {
+                       MidiBuffer::TimeType *tme = i.timeptr();
+                       // XXX need to subtract port offsets before scaling
+                       // also we must only scale events read from disk
+                       // and not existing input data in the buffer.
+                       *tme = (*tme) * nframes / disk_samples_to_consume;
+               }
+       }
+
+       if (ms & MonitoringInput) {
+               dst.merge_from (*target, nframes);
+       }
+
+#if 0
+       if (!target->empty ()) {
+               cerr << "======== MIDI OUT ========\n";
+               for (MidiBuffer::iterator i = target->begin(); i != target->end(); ++i) {
+                       const Evoral::Event<MidiBuffer::TimeType> ev (*i, false);
+                       cerr << "MIDI EVENT (from disk) @ " << ev.time();
+                       for (size_t xx = 0; xx < ev.size(); ++xx) {
+                               cerr << ' ' << hex << (int) ev.buffer()[xx];
+                       }
+                       cerr << dec << endl;
+               }
+               cerr << "----------------\n";
+       }
+#endif
+#if 0
+       cerr << "======== MIDI Disk Buffer ========\n";
+       _midi_buf->dump (cerr);
+       cerr << "----------------\n";
+#endif
+}
+
+/** @a start is set to the new sample position (TIME) read up to */
+int
+DiskReader::midi_read (samplepos_t& start, samplecnt_t dur, bool reversed)
+{
+       samplecnt_t this_read   = 0;
+       samplepos_t loop_end    = 0;
+       samplepos_t loop_start  = 0;
+       samplecnt_t loop_length = 0;
+       Location*  loc         = _loop_location;
+       samplepos_t effective_start = start;
+       Evoral::Range<samplepos_t>*  loop_range (0);
+
+       DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("MDS::midi_read @ %1 cnt %2\n", start, dur));
+
+       boost::shared_ptr<MidiTrack> mt = boost::dynamic_pointer_cast<MidiTrack>(_route);
+       MidiChannelFilter* filter = mt ? &mt->playback_filter() : 0;
+       sampleoffset_t loop_offset = 0;
+
+       if (!reversed && loc) {
+               get_location_times (loc, &loop_start, &loop_end, &loop_length);
+       }
+
+       while (dur) {
+
+               /* take any loop into account. we can't read past the end of the loop. */
+
+               if (loc && !reversed) {
+
+                       if (!loop_range) {
+                               loop_range = new Evoral::Range<samplepos_t> (loop_start, loop_end-1); // inclusive semantics require -1
+                       }
+
+                       /* if we are (seamlessly) looping, ensure that the first sample we read is at the correct
+                          position within the loop.
+                       */
+
+                       effective_start = loop_range->squish (effective_start);
+
+                       if ((loop_end - effective_start) <= dur) {
+                               /* too close to end of loop to read "dur", so
+                                  shorten it.
+                               */
+                               this_read = loop_end - effective_start;
+                       } else {
+                               this_read = dur;
+                       }
+
+               } else {
+                       this_read = dur;
+               }
+
+               if (this_read == 0) {
+                       break;
+               }
+
+               this_read = min (dur,this_read);
+
+               DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("MDS ::read at %1 for %2 loffset %3\n", effective_start, this_read, loop_offset));
+
+               if (midi_playlist()->read (*_midi_buf, effective_start, this_read, loop_range, 0, filter) != this_read) {
+                       error << string_compose(
+                                       _("MidiDiskstream %1: cannot read %2 from playlist at sample %3"),
+                                       id(), this_read, start) << endmsg;
+                       return -1;
+               }
+
+               g_atomic_int_add (&_samples_written_to_ringbuffer, this_read);
+
+               if (reversed) {
+
+                       // Swap note ons with note offs here.  etc?
+                       // Fully reversing MIDI requires look-ahead (well, behind) to find previous
+                       // CC values etc.  hard.
+
+               } else {
+
+                       /* adjust passed-by-reference argument (note: this is
+                          monotonic and does not reflect looping.
+                       */
+                       start += this_read;
+
+                       /* similarly adjust effective_start, but this may be
+                          readjusted for seamless looping as we continue around
+                          the loop.
+                       */
+                       effective_start += this_read;
+               }
+
+               dur -= this_read;
+       }
+
+       return 0;
+}
+
+int
+DiskReader::refill_midi ()
+{
+       if (!_playlists[DataType::MIDI]) {
+               return 0;
+       }
+
+       const size_t  write_space = _midi_buf->write_space();
+       const bool reversed    = _session.transport_speed() < 0.0f;
+
+       DEBUG_TRACE (DEBUG::DiskIO, string_compose ("MIDI refill, write space = %1 file sample = %2\n", write_space, file_sample[DataType::MIDI]));
+
+       /* no space to write */
+       if (write_space == 0) {
+               return 0;
+       }
+
+       if (reversed) {
+               return 0;
+       }
+
+       /* at end: nothing to do */
+
+       samplepos_t ffm = file_sample[DataType::MIDI];
+
+       if (ffm == max_samplepos) {
+               return 0;
+       }
+
+       int ret = 0;
+       const uint32_t samples_read = g_atomic_int_get (&_samples_read_from_ringbuffer);
+       const uint32_t samples_written = g_atomic_int_get (&_samples_written_to_ringbuffer);
+
+       if ((samples_read < samples_written) && (samples_written - samples_read) >= midi_readahead) {
+               return 0;
+       }
+
+       samplecnt_t to_read = midi_readahead - ((samplecnt_t)samples_written - (samplecnt_t)samples_read);
+
+       to_read = min (to_read, (samplecnt_t) (max_samplepos - ffm));
+       to_read = min (to_read, (samplecnt_t) write_space);
+
+       if (midi_read (ffm, to_read, reversed)) {
+               ret = -1;
+       }
+
+       file_sample[DataType::MIDI] = ffm;
+
+       return ret;
+}
+
+void
+DiskReader::set_no_disk_output (bool yn)
+{
+       /* this MUST be called as part of the process call tree, before any
+          disk readers are invoked. We use it when the session needs the
+          transport (and thus effective read position for DiskReaders) to keep
+          advancing as part of syncing up with a transport master, but we
+          don't want any actual disk output yet because we are still not
+          synced.
+       */
+       _no_disk_output = yn;
 }