ffmpeg convert mp4 through go exec

ffmpeg.go

package main

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

func main() {
	fi, _ := ioutil.ReadFile("test-4k.mp4")

	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 logErr(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

func runFFMPEGFromStdin(populate_stdin_func func(io.WriteCloser)) {
	cmd := exec.Command("ffmpeg", NewFFMpeg().args...)
	fmt.Println(cmd)

	// std err
	stderr, err := cmd.StderrPipe()
	logErr(err)

	stdin, err := cmd.StdinPipe()
	logErr(err)

	stdout, err := cmd.StdoutPipe()
	logErr(err)

	err = cmd.Start()
	logErr(err)

	go populate_stdin_func(stdin)

	fo, err := os.Create("output.mp4")
	logErr(err)
	defer fo.Close()

	_, err = io.Copy(fo, stdout)
	logErr(err)

	errFo, err := os.Create("output.log")
	logErr(err)
	defer errFo.Close()

	_, err = io.Copy(errFo, stderr)
	logErr(err)

	err = cmd.Wait()
	logErr(err)
}

type FFMpeg struct {
	cmd  string
	args []string
}

func NewFFMpeg() *FFMpeg {
	return &FFMpeg{
		cmd: "ffmpeg",
		args: []string{
			"-y",
			"-hide_banner",
			"-i",
			"pipe:0",
			"-c:v",
			"libx264",
			"-c:a",
			"aac",
			"-vf",
			"scale=640x360",
			"-t",
			"30",
			"-an",
			"-movflags",
			"frag_keyframe+empty_moov",
			"-f",
			"mp4",
			"-",
			// "out.mp4",
		},
	}
}