midi_synthesizer.py

from threading import Lock

import fluidsynth
import numpy as np


class MidiSynthesizer:
    def __init__(self, soundfont_path, sample_rate=44100):
        self.soundfont_path = soundfont_path
        self.sample_rate = sample_rate
        fl = fluidsynth.Synth(samplerate=float(sample_rate))
        sfid = fl.sfload(soundfont_path)
        self.devices = [[fl, sfid, False]]
        self.file_lock = Lock()

    def get_fluidsynth(self):
        for device in self.devices:
            if not device[2]:
                device[2] = True
                return device
        with self.file_lock:
            fl = fluidsynth.Synth(samplerate=float(self.sample_rate))
            sfid = fl.sfload(self.soundfont_path)
        device = [fl, sfid, True]
        self.devices.append(device)
        return device

    def release_fluidsynth(self, device):
        device[0].system_reset()
        device[0].get_samples(self.sample_rate*5) # wait for silence
        device[2] = False

    def synthesis(self, midi_opus):
        ticks_per_beat = midi_opus[0]
        event_list = []
        for track_idx, track in enumerate(midi_opus[1:]):
            abs_t = 0
            for event in track:
                abs_t += event[1]
                event_new = [*event]
                event_new[1] = abs_t
                event_list.append(event_new)
        event_list = sorted(event_list, key=lambda e: e[1])

        tempo = int((60 / 120) * 10 ** 6)  # default 120 bpm
        ss = np.empty((0, 2), dtype=np.int16)
        device = self.get_fluidsynth()
        fl, sfid = device[:-1]
        last_t = 0
        for c in range(16):
            fl.program_select(c, sfid, 128 if c == 9 else 0, 0)
        for event in event_list:
            name = event[0]
            sample_len = int(((event[1] / ticks_per_beat) * tempo / (10 ** 6)) * self.sample_rate)
            sample_len -= int(((last_t / ticks_per_beat) * tempo / (10 ** 6)) * self.sample_rate)
            last_t = event[1]
            if sample_len > 0:
                sample = fl.get_samples(sample_len).reshape(sample_len, 2)
                ss = np.concatenate([ss, sample])
            if name == "set_tempo":
                tempo = event[2]
            elif name == "patch_change":
                c, p = event[2:4]
                fl.program_select(c, sfid, 128 if c == 9 else 0, p)
            elif name == "control_change":
                c, cc, v = event[2:5]
                fl.cc(c, cc, v)
            elif name == "note_on" and event[3] > 0:
                c, p, v = event[2:5]
                fl.noteon(c, p, v)
            elif name == "note_off" or (name == "note_on" and event[3] == 0):
                c, p = event[2:4]
                fl.noteoff(c, p)

        self.release_fluidsynth(device)
        if ss.shape[0] > 0:
            max_val = np.abs(ss).max()
            if max_val != 0:
                ss = (ss / max_val) * np.iinfo(np.int16).max
        ss = ss.astype(np.int16)
        return ss