.go

package main

import (
	"math"
	"os"
	"time"

	"github.com/faiface/beep"
	"github.com/faiface/beep/mp3"
	"github.com/faiface/beep/speaker"
)

func main() {
	f, _ := os.Open("04 Harder, Better, Faster, Stronger.mp3")
	s, format, _ := mp3.Decode(f)

	sr := format.SampleRate

	speaker.Init(sr, sr.N(time.Second/30))

	start := time.Now()
	speaker.Play(beep.Iterate(func() beep.Streamer {
		speedChange := (math.Sin(time.Since(start).Seconds()/2)+1)*1.5 + 0.5
		newSampleRate := beep.SampleRate(float64(sr) / speedChange)
		return beep.Resample(4, sr, newSampleRate, beep.Take(sr.N(time.Second/5), s))
	}))

	select {}
}