Plays the Happy Birthday song via PCM using hajimehoshi's oto lib

happy_birthday.go

package main

import (
	"github.com/hajimehoshi/oto"
	"log"
	"math"
	"strings"
)

const defaultNumChannels = 2
const defaultBytesPerSample = 2
const defaultSampleRate = 44100
const defaultBufferSize = 8192

var notePosition = 0

// Note: there is no release or envelope so two notes together sound pretty lame in this example
var happyBirthday = "G4 G4 A4 G4 C5 B4 | G4 G4 A4 G4 D5 C5 | G4 G4 G5 E5 C5 B4 A4 | F5 F5 E5 C5 D5 C5 | |"

func main() {
	player, err := oto.NewPlayer(defaultSampleRate, defaultNumChannels, defaultBytesPerSample, defaultBufferSize)
	if err != nil {
		log.Fatal(err)
	}

	player.SetUnderrunCallback(func() {
		log.Println("SLOW CODE!")
	})

	vals := []uint8{}

	note := 392.00 // G4 default

	pitches := map[string]float64{
		"C4": 261.63, "D4": 293.66, "E4": 329.63, "F4": 349.23, // C4 - B5
		"G4": 392.00, "A4": 440.00, "B4": 493.88,
		"C5": 523.25, "D5": 587.33, "E5": 659.25, "F5": 698.46,
		"G5": 783.99, "A5": 880.00, "B5": 987.77,
	}

	for sampleTick := 0; sampleTick <= defaultSampleRate+1; sampleTick++ {
		if sampleTick >= defaultSampleRate {
			sampleTick = 0
		}

		if len(vals) >= 8192 {
			player.Write(vals)
			vals = []uint8{} // clear buffer
			continue
		}

		/*
			44100 is sample bytes per one second, so sampleTick @ 22050 is 0.5s
			120 bpm = 2 beats per second = 2 seconds per bar
			1 beat per second = 0.5s
			sampleTick == 22050 == 1 beat == 0.5s
			sampleTick == 11025 == 2/4notes == 0.25s
		*/
		if sampleTick%22050 == 1 {
			noteFreq := getNextNote()
			if noteFreq != "|" {
				note = pitches[noteFreq]
			}
		}

		deltaTime := 1 / float64(defaultSampleRate)
		frequency := note * deltaTime
		at := float64(sampleTick) * frequency

		sinePoint := deltaToSin(at)
		val := Uint16ToUInt8(floatToInt(sinePoint))

		vals = append(vals, val[1], val[0], val[1], val[0])
	}
}

func getNextNote() string {
	happyBirthdayNotes := strings.Split(happyBirthday, " ")

	if notePosition == len(happyBirthdayNotes) {
		notePosition = 0
	}

	note := happyBirthdayNotes[notePosition]
	notePosition++

	log.Println(note)

	return note
}

func deltaToSin(at float64) float64 {
	return math.Sin(at * math.Pi * 2.0)
}

func floatToInt(at float64) uint16 {
	at = at + 1     // add 1 to remove negative
	at = at / 2     // bring back into 0-1 range
	at = at * 65536 // make it uint16 wide
	return uint16(at)
}

func Uint16ToUInt8(at uint16) []uint8 {
	var h, l uint8 = uint8(at >> 8), uint8(at & 0xff)
	return []uint8{h, l}
}