yout.go

if currentEnv == prodEnv {
	out, err := exec.Command("which", "youtube-dl").CombinedOutput()
	if err != nil {
		log.Printf("unable to autodetect youtube-dl path: %v\n", err)
	} else {
		YoutubeDLPath = string(bytes.TrimSpace(out))
	}
}
func pipeThruFfmpegToMp4(vi *VideoInfo, rw web.ResponseWriter) error {
	var ffmpeg *exec.Cmd
	if vi.GetEndTime() == -1 {
		if vi.GetStartTime() == 0 {
			ffmpeg = exec.Command(
				"ffmpeg",
				"-thread_queue_size", "5120",
				"-i", "-",
				"-thread_queue_size", "5120",
				"-i", "pipe:3",
				"-c:v", "copy",
				"-c:a", "copy",
				"-movflags", "frag_keyframe+empty_moov+faststart", "-frag_duration", "3600",
				"-f", "mp4",
				"-")
		} else {
			ffmpeg = exec.Command(
				"ffmpeg",
				"-thread_queue_size", "5120",
				"-i", "-",
				"-ss", fmt.Sprintf("%.0f", vi.GetStartTime()),
				"-thread_queue_size", "5120",
				"-i", "pipe:3",
				"-ss", fmt.Sprintf("%.0f", vi.GetStartTime()),
				"-c:v", "copy",
				"-c:a", "copy",
				"-movflags", "frag_keyframe+empty_moov+faststart", "-frag_duration", "3600",
				"-f", "mp4",
				"-")
		}
	} else {
		ffmpeg = exec.Command(
			"ffmpeg",
			"-thread_queue_size", "5120",
			"-i", "-",
			"-thread_queue_size", "5120",
			"-i", "pipe:3",
			"-ss", fmt.Sprintf("%.0f", vi.GetStartTime()),
			"-to", fmt.Sprintf("%.0f", vi.GetEndTime()),
			"-c:v", "copy",
			"-c:a", "copy",
			"-movflags", "frag_keyframe+empty_moov+faststart", "-frag_duration", "3600",
			"-f", "mp4",
			"-")
	}
	youtubedlvideo := exec.Command(YoutubeDLPath, "--verbose", "-c", "--no-part", "-f", fmt.Sprintf("%s/bestvideo[ext=mp4]/bestvideo/best", vi.GetFormat()),  "--no-geo-bypass", "--no-cache-dir", "--hls-prefer-native", "-o", "-", fmt.Sprintf("%s", vi.GetVideoUrl()))
	youtubedl := exec.Command(YoutubeDLPath, "--verbose", "-c", "--no-part", "-f", "bestaudio[ext=m4a]/bestaudio/best", "--no-geo-bypass", "--no-cache-dir", "--hls-prefer-native", "-o", "-", fmt.Sprintf("%s", vi.GetVideoUrl()))
	youtubedl.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
	youtubedlvideo.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
	ffmpeg.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}

	var ytvbuf, ytbuf, ffbuf bytes.Buffer
	youtubedlvideo.Stderr = &ytvbuf
	youtubedl.Stderr = &ytbuf
	ffmpeg.Stderr = &ffbuf

	video, err := youtubedlvideo.StdoutPipe()
	if err != nil {
		log.Printf("pipeThruFfmpegToMp4: %v\n", err)
		return err
	}

	pipe3, err := youtubedl.StdoutPipe()
	if err != nil {
		log.Printf("pipeThruFfmpegToMp4: %v\n", err)
		return err
	}

	ffmpeg.Stdin = video
	ffmpeg.ExtraFiles = []*os.File{pipe3.(*os.File)}
	ffmpeg.Stdout = rw

	ffmpegdir, err := ioutil.TempDir("", "ffmpegdirmp4")
	if err != nil {
		log.Fatal(err)
	}

	defer os.RemoveAll(ffmpegdir) // clean up

	youtubedldir, err := ioutil.TempDir("", "youtubedldirmp4")
	if err != nil {
		log.Fatal(err)
	}

	defer os.RemoveAll(youtubedldir) // clean up

	youtubedlvideodir, err := ioutil.TempDir("", "youtubedlvideodirmp4")
	if err != nil {
		log.Fatal(err)
	}

	defer os.RemoveAll(youtubedlvideodir) // clean up
	ffmpeg.Dir = ffmpegdir
	youtubedl.Dir = youtubedldir
	youtubedlvideo.Dir = youtubedlvideodir

	// Headers sent, no turning back now
	rw.Header().Set("Content-Type", "video/mp4")
	rw.Header().Set("Content-Disposition", fmt.Sprintf("attachment;filename=\"%s.mp4\"", vi.GetSlug()))
	rw.Flush()

	ffmpeg.Start()
	youtubedlvideo.Start()
	youtubedl.Start()
	ffmpeg.Wait()
	syscall.Kill(-youtubedl.Process.Pid, syscall.SIGKILL)
	syscall.Kill(-youtubedlvideo.Process.Pid, syscall.SIGKILL)
	syscall.Kill(-ffmpeg.Process.Pid, syscall.SIGKILL)
	youtubedlvideo.Wait()
	youtubedl.Wait()

	// check ytvbuf, ytbuf, ffbuf for stderr errors

	if ffbuf.Len() != 0 {
		rollbar.Error(rollbar.ERR, err, &rollbar.Field{"stderr", ffbuf.String()})
		log.Printf("pipeThruFfmpegToMp4: %v\n", ffbuf.String())
	}
	if ytvbuf.Len() != 0 {
		rollbar.Error(rollbar.ERR, err, &rollbar.Field{"stderr", ytvbuf.String()})
		log.Printf("pipeThruYouTubeDLToMp4: %v\n", ytvbuf.String())
	}
	if ytbuf.Len() != 0 {
		rollbar.Error(rollbar.ERR, err, &rollbar.Field{"stderr", ytbuf.String()})
		log.Printf("pipeThruYouTubeDLToMp4: %v\n", ytbuf.String())
	}

	return nil
}