Source code for stage.midi

"""midi.py

MIDI event processing objects common to several scripts.  Uses the mido library for MIDI file and endpoint I/O."""

import logging
import time

import mido

# initialize logging for this module
log = logging.getLogger('MIDI')

#================================================================


def decode_mpd218_key(key):
    """Interpret a MPD218 pad event note value as a row, column, and bank position.
    Row 0 is the front/bottom row (Pads 1-4), row 3 is the back/top row (Pads 13-16).
    Column 0 is the left, column 3 is the right.
    Bank 0 is the A bank, bank 1 is the B bank, bank 2 is the C bank.

    :param key: an integer MIDI note value
    :return: (row, column, bank)

    """
    # Decode the key into coordinates on the 4x4 pad grid.
    bank = (key - 36) // 16
    pos = (key - 36) % 16
    row = pos // 4
    col = pos % 4
    return row, col, bank


#================================================================


class Receiver:
    """Use the mido library to create a MIDI endpoint.  Real-time events are
    received on a background thread and passed to a user-supplied callback."""

    def __init__(self, args, midi_endpoint, event_callback):

        # Open the MIDI input port
        names = mido.get_input_names()
        if midi_endpoint in names:
            self.midi_port = mido.open_input(midi_endpoint)
        else:
            log.warning("Requested MIDI input %s not available in %s", midi_endpoint, names)
            self.midi_port = mido.open_input(names[0])
        log.info("Opened MIDI input port %s", self.midi_port.name)

        # Note: callbacks will arrive on a different thread.  This should be
        # fine since the translation system is stateless, all MIDI messages
        # simply generate OSC output, and the underlying network code should be
        # thread-safe.
        self.midi_port.callback = event_callback

        return



    def close(self):
        self.midi_port.close()



#================================================================


class Player:
    """MIDI file player."""

    def __init__(self, args, filename, callback):

        self.verbose = args.verbose
        self.event_callback = callback

        self.midifile = mido.MidiFile(filename)
        self.log_midifile_metadata(filename, self.midifile)

        # MIDI files express tempo as microseconds per quarter note; this sets
        # a default tempo of 120 BPM (0.5 sec per beat).
        self.midi_tempo = 500000

        # MIDI files express times in integer ticks per quarter note.
        self.ticks_per_beat = self.midifile.ticks_per_beat

        # Merge all tracks (if more than one) into a single track in time order.
        # This assumes that events are identified by channel number for routing
        # and not simply by track.
        self.playtrack = mido.merge_tracks(self.midifile.tracks)

        return



    def close(self):
        pass


    #--------------------------------------------------------------------


    def log_midifile_metadata(self, filename, midifile):
        log.info("Opened MIDI file %s, MIDI format %d, %d tracks, %d ticks per beat",
                 filename, midifile.type, len(midifile.tracks), midifile.ticks_per_beat)

        for i, track in enumerate(midifile.tracks):
            log.info("MIDI file track %d: %s", i, track.name)

        # report some diagnostics on the current midifile to the log
        for track in midifile.tracks:
            log.info("Contents of track '%s'", track.name)
            event_messages = 0
            for msg in track:
                if msg.is_meta:
                    log.info("MIDI metadata: %s", msg)
                else:
                    event_messages += 1
            # end of track
            log.info("Track '%s' includes %d events.", track.name, event_messages)


    #--------------------------------------------------------------------


    def perform_event(self, event):
        # ignore metadata messages track_name, instrument_name, key_signature, smpte_offset, etc.
        if event.type == 'set_tempo':
            log.info("MIDI tempo change: %d usec/beat (%f BPM).", event.tempo, mido.tempo2bpm(event.tempo))
            self.midi_tempo = event.tempo

        elif event.type in ['note_on', 'note_off']:
            log.debug("Note On: channel %d, note %d, velocity %d", event.channel, event.note, event.velocity)
            self.event_callback(event)


    #--------------------------------------------------------------------


    def run(self, skip=0):
        """Run one performance of the MIDI file and return.  Eeach MIDI event is
        issued in real time as OSC network messages translated via the MIDI to
        OSC bridge object."""

        # Keep track of target times in integer nanoseconds to avoid roundoff
        # errors.  Following an absolute clock will maintain overall precision
        # in the presence of sleep time jitter.
        start_t = time.monotonic_ns()
        next_timepoint = start_t

        # play through all the events in the sequence, waiting the specified
        # number of ticks before each issue
        for event in self.playtrack:

            if self.verbose:
                log.debug("Playing event: %s", event)

            # don't perform the end of track, it can have an unreasonable delay
            if event.type == 'end_of_track':
                log.info("Found end event: %s", event)
                return

            if skip > 0:
                skip -= 1

            else:
                # if the next event has a preceding delay, convert from ticks
                # at the current tempo to an absolute time in nanoseconds
                if event.time > 0:
                    event_ns = event.time * 1000 * self.midi_tempo / self.ticks_per_beat
                    next_timepoint += event_ns
                    delay_ns = next_timepoint - time.monotonic_ns()
                    if delay_ns > 0:
                        time.sleep(delay_ns * 1e-9)

                self.perform_event(event)



#================================================================