convert_audio.go

func populateStdin(file []byte) func(io.WriteCloser) {
	return func(stdin io.WriteCloser) {
		defer stdin.Close()
		io.Copy(stdin, bytes.NewReader(file))
		fmt.Println("copied ok")
	}
}

func audio_m4a2mp3(data []byte) ([]byte, error) {
	binary, lookErr := exec.LookPath("ffmpeg")
	if lookErr != nil {
		return nil, fmt.Errorf("not found ffmpeg: %v\n", lookErr)
	}

	//ffmpeg := exec.Command(binary, "-i", "pipe:0", "-map", "0:a", "-b:a", "24k", "-f", "mp3", "pipe:1")
	ffmpeg := exec.Command(binary, "-i", "pipe:0", "-ab", "24k", "-f", "mp3", "pipe:1")
	stdin, _ := ffmpeg.StdinPipe()
	stdout, _ := ffmpeg.StdoutPipe()
	//stderr, _ := ffmpeg.StderrPipe()

	//echo := exec.Command("echo", os.Getenv("PATH"))
	//tmpout, _ := echo.StdoutPipe()
	//echo.Start()
	//go io.Copy(os.Stdout, tmpout)

	if err := ffmpeg.Start(); err != nil {
		return nil, fmt.Errorf("exec error, %v\n", err)
	}
	fmt.Println("started")

	go populateStdin(data)(stdin)
	//go io.Copy(os.Stderr, stderr)
	fmt.Println("input ok")

	data2, err := ioutil.ReadAll(stdout)
	if err != nil {
		return nil, fmt.Errorf("readall error, %v\n", err)
	}

	//TODO for more tests
	//http://stackoverflow.com/questions/11886531/terminating-a-process-started-with-os-exec-in-golang
	done := make(chan error, 1)
	go func() {
		done <- ffmpeg.Wait()
	}()
	select {
	case <-time.After(3 * time.Second):
		if err := ffmpeg.Process.Kill(); err != nil {
			log.Fatal("failed to kill: ", err)
		}
		<-done // allow goroutine to exit
		return nil, fmt.Errorf("process killed")
	case err := <-done:
		if err != nil {
			return nil, err
		}
	}

	return data2, err
}