Buffer changes time read

[sheerun]

package main

import (
	"fmt"
	"log"
	"os"
	"time"

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

func main() {
	f, err := os.Open("/Users/sheerun/Music/West/foo.mp3")
	if err != nil {
		log.Fatal(err)
	}
	streamer, format, err := mp3.Decode(f)
	if err != nil {
		log.Fatal(err)
	}
	defer streamer.Close()

	speaker.Init(format.SampleRate, format.SampleRate.N(time.Second))

	done := make(chan bool)
	speaker.Play(beep.Seq(streamer, beep.Callback(func() {
		done <- true
	})))

	speaker.Lock()
	fmt.Println(format.SampleRate.D(streamer.Position()).Round(time.Second))
	speaker.Unlock()

	for {
		select {
		case <-done:
			return
		case <-time.After(time.Second):
			speaker.Lock()
			fmt.Println(format.SampleRate.D(streamer.Position()))
			speaker.Unlock()
		}
	}
}

As you see I've used format.SampleRate.N(time.Second) rather than format.SampleRate.N(time.Second/10) in the readme to prevent issues with streaming audio due to slow CPU.

Now the logs say following:

go run main.go
0s
4s
5s
6s

First of all it seems that 3 seconds are buffered instead of 1

Secondly it seems that reading time depends on size of buffer which is confusing. Could I read position of speaker maybe instead? I'd expect to see:

go run main.go
0s
1s
2s
3s

Regardless of the buffer size