bi

package main

import (
   "fmt"
   "io"
   "io/ioutil"
   "os"
   "os/exec"
   "path/filepath"
)

func main() {
   args := os.Args[1:]
   if len(args) < 2 {
      fmt.Println( "usage: src dst")
      return
   }
   b, err := transform(args...)
   if err != nil {
      fmt.Println(err)
      return
   }
   fmt.Print(string(b))
}

func copy(w io.Writer, r io.Reader) error {
   header := make([]byte, 9)
   _, err := io.ReadFull(r, header)
   if err != nil {
      return err
   }
   _, err = io.Copy(w, r)
   return err
}

func find(root, ext string) ([]string, error) {
   var files []string
   err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
      if err != nil {
         return err
      }
      if filepath.Ext(path) == ext {
         files = append(files, path)
      }
      return nil
   })
   return files, err
}

func transform(args ...string) ([]byte, error) {
   const suffix = ".m4s"
   files, err := find(args[0], suffix)
   if err != nil {
      return nil, err
   }

   tmp := make([]string, 2)
   if len(files) < len(tmp) {
      return nil, fmt.Errorf("can't find enough m4s")
   }

   for i, _ := range tmp {
      //base := filepath.Base(files[i]) base[:len(base)-len(suffix)] + ".mp4"
      t, err := ioutil.TempFile("", "*.mp4")
      if err != nil {
         return nil, err
      }

      tmp[i] = t.Name()
      r, err := os.Open(files[i])
      if err != nil {
         return nil, err
      }
      err = copy(t, r)
      if err != nil {
         return nil, err
      }

      err = t.Close()
      if err != nil {
         return nil, err
      }
      err = r.Close()
      if err != nil {
         return nil, err
      }
      defer os.Remove(t.Name())
   }

   args = append([]string{"-i", tmp[0], "-i", tmp[1], "-acodec", "copy", "-vcodec", "copy"}, args[1:]...)
   cmd := exec.Command("ffmpeg", args...)
   return cmd.Output()
}