musicutil/utils/transcoder/transcoder.go

package transcoder

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"math"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"time"

	"gitlab.com/ChaotiCryptidz/musicutil/types"
)

type TranscodeConfig struct {
	UseQuality    bool   `json:"use_quality"`
	UseBitrate    bool   `json:"use_bitrate"`
	Encoder       string `json:"encoder"`
	FileExtension string `json:"file_extension"`
	Container     string `json:"container"`
	Bitrate       string `json:"bitrate"`
	Quality       string `json:"quality"`
	SampleRate    string `json:"sample_rate"`
	Channels      string `json:"channels"`
}

func isNotEmptyString(x string) bool {
	if len(strings.TrimSpace(x)) == 0 {
		return false
	}

	return true
}

func progressDurationToMilliSeconds(duration string) int64 {
	fields := strings.Split(strings.TrimSpace(duration), ":")
	durationNs := int64(0)

	h, _ := strconv.ParseInt(fields[0], 10, 64)
	durationNs += int64(time.Hour) * h

	m, _ := strconv.ParseInt(fields[1], 10, 64)
	durationNs += int64(time.Minute) * m

	s, _ := strconv.ParseFloat(fields[2], 64)
	durationNs += int64(float64(time.Second) * s)

	return time.Duration(durationNs).Milliseconds()
}

func getFileLengthMilliSeconds(filename string) (int64, error) {
	type FFProbeFormat struct {
		Duration string `json:"duration"`
	}
	type FFProbeOutput struct {
		Format FFProbeFormat `json:"format"`
	}

	ffprobe_output_str, err := exec.Command(
		"ffprobe",
		"-v", "quiet",
		"-print_format", "json",
		"-show_format",
		filename,
	).Output()

	if err != nil {
		return 0, err
	}

	var ffprobe_output FFProbeOutput
	err = json.Unmarshal([]byte(ffprobe_output_str), &ffprobe_output)
	if err != nil {
		return 0, err
	} else {
		duration_str := ffprobe_output.Format.Duration
		duration_float, err := strconv.ParseFloat(duration_str, 64)
		if err != nil {
			return 0, err
		}

		duration_millis := int64(math.Round(duration_float * 1000))
		return duration_millis, nil
	}
}

func Transcode(file *types.File, config *TranscodeConfig, progress_chan chan string, dest string) (string, error) {
	command_args := make([]string, 0)
	command_args = append(command_args, "-y")
	command_args = append(command_args, "-hide_banner")

	command_args = append(command_args, "-i")
	command_args = append(command_args, file.JoinPathTo())

	if isNotEmptyString(config.Encoder) {
		command_args = append(command_args, "-c:a")
		command_args = append(command_args, config.Encoder)
	}

	if isNotEmptyString(config.Container) {
		command_args = append(command_args, "-f")
		command_args = append(command_args, config.Container)
	}

	if isNotEmptyString(config.SampleRate) {
		command_args = append(command_args, "-ar")
		command_args = append(command_args, config.SampleRate)
	}

	if isNotEmptyString(config.Channels) {
		command_args = append(command_args, "-ac")
		command_args = append(command_args, config.Channels)
	}

	if config.UseQuality {
		command_args = append(command_args, "-q:a")
		command_args = append(command_args, config.Quality)
	}

	if config.UseBitrate {
		command_args = append(command_args, "-b:a")
		command_args = append(command_args, config.Bitrate)
	}

	command_args = append(command_args, dest)

	// Progress Shenanigans

	if progress_chan != nil {
		total_length_milliseconds, err := getFileLengthMilliSeconds(file.JoinPathTo())
		if err != nil {
			goto end
		}

		progress_temp_dir, err := os.MkdirTemp("", "*-musicutil_transcode_temp")
		if err != nil {
			goto end
		}
		defer os.RemoveAll(progress_temp_dir)

		progress_filename := progress_temp_dir + "/progress.log"
		progress_file, err := os.Create(progress_filename)
		if err != nil {
			goto end
		}
		defer os.Remove(progress_filename)

		command_args = append(command_args, "-progress", progress_filename, "-nostats")

		go func() {
			reader := bufio.NewReader(progress_file)
			for {
				line, err := reader.ReadBytes('\n')
				if err == nil {
					if strings.HasPrefix(string(line), "out_time=") {
						out_time := strings.TrimSuffix(strings.TrimPrefix(string(line), "out_time="), "\n")
						out_time_ms := progressDurationToMilliSeconds(out_time)

						progress_chan <- fmt.Sprintf("%0.2f%%", (float64(out_time_ms) / float64(total_length_milliseconds) * 100))
					}
				}
			}
		}()
	}

end:
	cmd := exec.Command("ffmpeg", command_args...)
	output, err := cmd.CombinedOutput()
	if err != nil {
		fmt.Println(output)
		return string(output), errors.New("ffmpeg error")
	}

	if progress_chan != nil {
		close(progress_chan)
	}
	return string(output), nil
}