Capture ffmpeg output when executed by Go os/exec pkg

go_exec_ffmpeg.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"os/exec"
	"regexp"
	"strings"
)

var (
	file = flag.String("file", "", "video file")
	rtmp = flag.String("rtmp", "", "RTMP URL")
)

func main() {
	flag.Parse()

	args := fmt.Sprintf("-re -i %s -c copy -f flv %s", *file, *rtmp)
	cmd := exec.Command("ffmpeg", strings.Split(args, " ")...)

	stdErr, err := cmd.StderrPipe()
	if err != nil {
		panic(err)
	}

	err = cmd.Start()
	if err != nil {
		panic(err)
	}

	scanner := bufio.NewScanner(stdErr)
	scanner.Split(rawScan)
	for scanner.Scan() {
		m := scanner.Text()
		info := info(m)
		if len(info) > 0 {
			fmt.Printf("%+v\n", info)
		}
	}

	err = cmd.Wait()
	if err != nil {
		fmt.Printf("err: %s\n", err)
		return
	}
	fmt.Println("finished")
}

func info(data string) map[string]string {
	myExp := regexp.MustCompile(`frame=(?P<frame>.*)fps=(?P<fps>.*)q=(?P<q>.*)size=(?P<size>.*)` +
		`time=(?P<time>.*)bitrate=(?P<bitrate>.*)speed=(?P<speed>.*)`)

	result := map[string]string{}
	if !myExp.Match([]byte(data)) {
		return result
	}

	matches := myExp.FindStringSubmatch(data)
	names := myExp.SubexpNames()
	for i, m := range matches {
		if names[i] == "" {
			continue
		}
		result[names[i]] = strings.TrimSpace(m)
	}
	return result
}

// dropCR drops a terminal \r from the data.
func dropCR(data []byte) []byte {
	if len(data) > 0 && data[len(data)-1] == '\r' {
		return data[0 : len(data)-1]
	}
	return data
}

func rawScan(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	return len(data), dropCR(data), nil
}