Add MIDI decoder

examples/midi/Buy to the Beat - V2 License.md

@@ -0,0 +1,6 @@
+# Buy to the Beat - V2
+
+Copyright (c) 2021 Robert Oost<br>
+Soundcloud: https://soundcloud.com/sponsrob
+
+This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) License. To view a copy of the license, visit https://creativecommons.org/licenses/by-nc-sa/4.0/.

examples/midi/Florestan-Basic-GM-GS License.md

@@ -0,0 +1,7 @@
+# Florestan Basic GM GS
+
+Author: Nando Florestan
+
+This sound font is in the public domain.
+
+Source: [Internet Archive](https://archive.org/details/sf2-soundfonts-free-use)

examples/midi/main.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"time"
+
+	"github.com/gopxl/beep"
+	"github.com/gopxl/beep/midi"
+	"github.com/gopxl/beep/speaker"
+)
+
+func main() {
+	var sampleRate beep.SampleRate = 44100
+
+	err := speaker.Init(sampleRate, sampleRate.N(time.Second/30))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Load a soundfont.
+	soundFontFile, err := os.Open("Florestan-Basic-GM-GS-by-Nando-Florestan(Public-Domain).sf2")
+	if err != nil {
+		log.Fatal(err)
+	}
+	soundFont, err := midi.NewSoundFont(soundFontFile)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Load a midi track.
+	midiFile, err := os.Open("Buy to the Beat - V2.mid")
+	if err != nil {
+		log.Fatal(err)
+	}
+	s, format, err := midi.Decode(midiFile, soundFont, sampleRate)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Song duration: %v\n", format.SampleRate.D(s.Len()))
+	speaker.PlayAndWait(s)
+}

go.mod

@@ -4,18 +4,19 @@ go 1.21
 
 require (
 	github.com/ebitengine/oto/v3 v3.2.0
+	github.com/ebitengine/purego v0.7.1
 	github.com/gdamore/tcell/v2 v2.7.4
 	github.com/hajimehoshi/go-mp3 v0.3.4
 	github.com/jfreymuth/oggvorbis v1.0.5
 	github.com/mewkiz/flac v1.0.10
 	github.com/orcaman/writerseeker v0.0.0-20200621085525-1d3f536ff85e
 	github.com/pkg/errors v0.9.1
+	github.com/samhocevar/go-meltysynth v0.0.0-20230403180939-aca4a036cb16
 	github.com/stretchr/testify v1.9.0
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/ebitengine/purego v0.7.1 // indirect
 	github.com/gdamore/encoding v1.0.0 // indirect
 	github.com/icza/bitio v1.1.0 // indirect
 	github.com/jfreymuth/vorbis v1.0.2 // indirect

go.sum

@@ -42,6 +42,8 @@ github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZN
 github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
 github.com/rivo/uniseg v0.4.3 h1:utMvzDsuh3suAEnhH0RdHmoPbU648o6CvXxTx4SBMOw=
 github.com/rivo/uniseg v0.4.3/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=
+github.com/samhocevar/go-meltysynth v0.0.0-20230403180939-aca4a036cb16 h1:slzh3BWJ6FyMM8gkDzDwHz+gjU4+82ldB6oPyYi82Ho=
+github.com/samhocevar/go-meltysynth v0.0.0-20230403180939-aca4a036cb16/go.mod h1:J+GU4sgu3oAPHCceoTIXNKzFHSybNhF/LyFkWZlqhvE=
 github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=

midi/decode.go

@@ -0,0 +1,139 @@
+// Package midi implements audio data decoding in MIDI format.
+package midi
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/pkg/errors"
+	"github.com/samhocevar/go-meltysynth/meltysynth"
+
+	"github.com/gopxl/beep"
+)
+
+const (
+	midiNumChannels = 2
+	midiPrecision   = 4
+)
+
+// NewSoundFont reads a sound font containing instruments. A sound font is required in order to play MIDI files.
+//
+// NewSoundFont closes the supplied ReadCloser.
+func NewSoundFont(r io.ReadCloser) (*SoundFont, error) {
+	sf, err := meltysynth.NewSoundFont(r)
+	if err != nil {
+		return nil, err
+	}
+	err = r.Close()
+	if err != nil {
+		return nil, err
+	}
+	return &SoundFont{sf}, nil
+}
+
+type SoundFont struct {
+	sf *meltysynth.SoundFont
+}
+
+// Decode takes a ReadCloser containing audio data in MIDI format and a SoundFont to synthesize the sounds
+// and returns a beep.StreamSeeker, which streams the audio.
+//
+// Decode closes the supplied ReadCloser.
+func Decode(rc io.ReadCloser, sf *SoundFont, sampleRate beep.SampleRate) (s beep.StreamSeeker, format beep.Format, err error) {
+	defer func() {
+		if err != nil {
+			err = errors.Wrap(err, "midi")
+		}
+	}()
+
+	settings := meltysynth.NewSynthesizerSettings(int32(sampleRate))
+	synth, err := meltysynth.NewSynthesizer(sf.sf, settings)
+	if err != nil {
+		return nil, beep.Format{}, err
+	}
+
+	mf, err := meltysynth.NewMidiFile(rc)
+	if err != nil {
+		return nil, beep.Format{}, err
+	}
+	err = rc.Close()
+	if err != nil {
+		return nil, beep.Format{}, err
+	}
+
+	seq := meltysynth.NewMidiFileSequencer(synth)
+	seq.Play(mf /*loop*/, false)
+
+	format = beep.Format{
+		SampleRate:  sampleRate,
+		NumChannels: midiNumChannels,
+		Precision:   midiPrecision,
+	}
+
+	return &decoder{
+		synth:      synth,
+		mf:         mf,
+		seq:        seq,
+		sampleRate: sampleRate,
+		bufLeft:    make([]float32, 512),
+		bufRight:   make([]float32, 512),
+	}, format, nil
+}
+
+type decoder struct {
+	synth             *meltysynth.Synthesizer
+	mf                *meltysynth.MidiFile
+	seq               *meltysynth.MidiFileSequencer
+	sampleRate        beep.SampleRate
+	bufLeft, bufRight []float32
+	err               error
+}
+
+func (d *decoder) Stream(samples [][2]float64) (n int, ok bool) {
+	if d.err != nil {
+		return 0, false
+	}
+
+	samplesLeft := d.Len() - d.Position()
+	if len(samples) > samplesLeft {
+		samples = samples[:samplesLeft]
+	}
+
+	for len(samples) > 0 {
+		cn := len(d.bufLeft)
+		if cn > len(samples) {
+			cn = len(samples)
+		}
+
+		d.seq.Render(d.bufLeft[:cn], d.bufRight[:cn])
+		for i := 0; i < cn; i++ {
+			samples[i][0] = float64(d.bufLeft[i])
+			samples[i][1] = float64(d.bufRight[i])
+		}
+
+		samples = samples[cn:]
+		n += cn
+	}
+
+	return n, n > 0
+}
+
+func (d *decoder) Err() error {
+	return d.err
+}
+
+func (d *decoder) Len() int {
+	return d.sampleRate.N(d.mf.GetLength())
+}
+
+func (d *decoder) Position() int {
+	return d.sampleRate.N(d.seq.Pos())
+}
+
+func (d *decoder) Seek(p int) error {
+	if p < 0 || d.Len() < p {
+		return fmt.Errorf("midi: seek position %v out of range [%v, %v]", p, 0, d.Len())
+	}
+	d.seq.Seek(d.sampleRate.D(p))
+	return nil
+}