A Go script to generate caption file (srt format) from text file

main.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
	"strings"
	"time"
)

const format = "15:04:05,000"
// configure this to change duration of each caption
const secondsToAdd = 3 * time.Second

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanLines)

	var b strings.Builder

	idx := 1
	now, err := time.Parse(format, "00:00:00,000")
	if err != nil {
		log.Fatalf("time.Parse: %v", err)
	}

	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			continue
		}

		b.WriteString(fmt.Sprintf("%d\n", idx))
		b.WriteString(fmt.Sprintf("%v --> %v\n", now.Format(format), now.Add(3*time.Second).Format(format)))
		b.WriteString(line)
		b.WriteString(fmt.Sprintln())
		b.WriteString(fmt.Sprintln())

		idx++
		now = now.Add(secondsToAdd)
	}

        fmt.Fprintln(os.Stdout, b.String())
}