Use ffmpeg through Go exec

package main

import (
    "io"
    "log"
    "os"
    "os/exec"
    "io/ioutil"
	"bytes"
)

func main() {
	fi, _ := ioutil.ReadFile("noir.aif")

    runFFMPEGFromStdin(populateStdin(fi))
}

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

func runFFMPEGFromStdin(populate_stdin_func func(io.WriteCloser)) {
    cmd := exec.Command("ffmpeg","-i","pipe:0","-ab","128k","-f","mp3","pipe:1")
    stdin, err := cmd.StdinPipe()
    if err != nil {
        log.Panic(err)
    }
    stdout, err := cmd.StdoutPipe()
    if err != nil {
        log.Panic(err)
    }
    err = cmd.Start()
    if err != nil {
        log.Panic(err)
    }
    populate_stdin_func(stdin)
	fo, _ := os.Create("output.mp3")
	io.Copy(fo, stdout)

    err = cmd.Wait()
    if err != nil {
        log.Panic(err)
    }
}