navidrome/core/ffmpeg/ffmpeg.go

package ffmpeg

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"sync"

	"github.com/navidrome/navidrome/conf"
	"github.com/navidrome/navidrome/log"
)

type FFmpeg interface {
	Transcode(ctx context.Context, command, path string, maxBitRate, offset int) (io.ReadCloser, error)
	ExtractImage(ctx context.Context, path string) (io.ReadCloser, error)
	ConvertToWAV(ctx context.Context, path string) (io.ReadCloser, error)
	ConvertToFLAC(ctx context.Context, path string) (io.ReadCloser, error)
	Probe(ctx context.Context, files []string) (string, error)
	CmdPath() (string, error)
	IsAvailable() bool
	Version() string
}

func New() FFmpeg {
	return &ffmpeg{}
}

const (
	extractImageCmd = "ffmpeg -i %s -an -vcodec copy -f image2pipe -"
	probeCmd        = "ffmpeg %s -f ffmetadata"
	createWavCmd    = "ffmpeg -i %s -c:a pcm_s16le -f wav -"
	createFLACCmd   = "ffmpeg -i %s -f flac -"
)

type ffmpeg struct{}

func (e *ffmpeg) Transcode(ctx context.Context, command, path string, maxBitRate, offset int) (io.ReadCloser, error) {
	if _, err := ffmpegCmd(); err != nil {
		return nil, err
	}
	args := createFFmpegCommand(command, path, maxBitRate, offset)
	return e.start(ctx, args)
}

func (e *ffmpeg) ExtractImage(ctx context.Context, path string) (io.ReadCloser, error) {
	if _, err := ffmpegCmd(); err != nil {
		return nil, err
	}
	args := createFFmpegCommand(extractImageCmd, path, 0, 0)
	return e.start(ctx, args)
}

func (e *ffmpeg) ConvertToWAV(ctx context.Context, path string) (io.ReadCloser, error) {
	args := createFFmpegCommand(createWavCmd, path, 0, 0)
	return e.start(ctx, args)
}

func (e *ffmpeg) ConvertToFLAC(ctx context.Context, path string) (io.ReadCloser, error) {
	args := createFFmpegCommand(createFLACCmd, path, 0, 0)
	return e.start(ctx, args)
}

func (e *ffmpeg) Probe(ctx context.Context, files []string) (string, error) {
	if _, err := ffmpegCmd(); err != nil {
		return "", err
	}
	args := createProbeCommand(probeCmd, files)
	log.Trace(ctx, "Executing ffmpeg command", "args", args)
	cmd := exec.CommandContext(ctx, args[0], args[1:]...) // #nosec
	output, _ := cmd.CombinedOutput()
	return string(output), nil
}

func (e *ffmpeg) CmdPath() (string, error) {
	return ffmpegCmd()
}

func (e *ffmpeg) IsAvailable() bool {
	_, err := ffmpegCmd()
	return err == nil
}

// Version executes ffmpeg -version and extracts the version from the output.
// Sample output: ffmpeg version 6.0 Copyright (c) 2000-2023 the FFmpeg developers
func (e *ffmpeg) Version() string {
	cmd, err := ffmpegCmd()
	if err != nil {
		return "N/A"
	}
	out, err := exec.Command(cmd, "-version").CombinedOutput() // #nosec
	if err != nil {
		return "N/A"
	}
	parts := strings.Split(string(out), " ")
	if len(parts) < 3 {
		return "N/A"
	}
	return parts[2]
}

func (e *ffmpeg) start(ctx context.Context, args []string) (io.ReadCloser, error) {
	log.Trace(ctx, "Executing ffmpeg command", "cmd", args)
	j := &ffCmd{args: args}
	j.PipeReader, j.out = io.Pipe()
	err := j.start()
	if err != nil {
		return nil, err
	}
	go j.wait()
	return j, nil
}

type ffCmd struct {
	*io.PipeReader
	out  *io.PipeWriter
	args []string
	cmd  *exec.Cmd
}

func (j *ffCmd) start() error {
	cmd := exec.Command(j.args[0], j.args[1:]...) // #nosec
	cmd.Stdout = j.out
	if log.IsGreaterOrEqualTo(log.LevelTrace) {
		cmd.Stderr = os.Stderr
	} else {
		cmd.Stderr = io.Discard
	}
	j.cmd = cmd

	if err := cmd.Start(); err != nil {
		return fmt.Errorf("starting cmd: %w", err)
	}
	return nil
}

func (j *ffCmd) wait() {
	if err := j.cmd.Wait(); err != nil {
		var exitErr *exec.ExitError
		if errors.As(err, &exitErr) {
			_ = j.out.CloseWithError(fmt.Errorf("%s exited with non-zero status code: %d", j.args[0], exitErr.ExitCode()))
		} else {
			_ = j.out.CloseWithError(fmt.Errorf("waiting %s cmd: %w", j.args[0], err))
		}
		return
	}
	_ = j.out.Close()
}

// Path will always be an absolute path
func createFFmpegCommand(cmd, path string, maxBitRate, offset int) []string {
	var args []string
	for _, s := range fixCmd(cmd) {
		if strings.Contains(s, "%s") {
			s = strings.ReplaceAll(s, "%s", path)
			args = append(args, s)
			if offset > 0 && !strings.Contains(cmd, "%t") {
				args = append(args, "-ss", strconv.Itoa(offset))
			}
		} else {
			s = strings.ReplaceAll(s, "%t", strconv.Itoa(offset))
			s = strings.ReplaceAll(s, "%b", strconv.Itoa(maxBitRate))
			args = append(args, s)
		}
	}

	return args
}

func createProbeCommand(cmd string, inputs []string) []string {
	var args []string
	for _, s := range fixCmd(cmd) {
		if s == "%s" {
			for _, inp := range inputs {
				args = append(args, "-i", inp)
			}
		} else {
			args = append(args, s)
		}
	}
	return args
}

func fixCmd(cmd string) []string {
	split := strings.Split(cmd, " ")
	var result []string
	cmdPath, _ := ffmpegCmd()
	for _, s := range split {
		if s == "ffmpeg" || s == "ffmpeg.exe" {
			result = append(result, cmdPath)
		} else {
			result = append(result, s)
		}
	}
	return result
}

func ffmpegCmd() (string, error) {
	ffOnce.Do(func() {
		if conf.Server.FFmpegPath != "" {
			ffmpegPath = conf.Server.FFmpegPath
			ffmpegPath, ffmpegErr = exec.LookPath(ffmpegPath)
		} else {
			ffmpegPath, ffmpegErr = exec.LookPath("ffmpeg")
			if errors.Is(ffmpegErr, exec.ErrDot) {
				log.Trace("ffmpeg found in current folder '.'")
				ffmpegPath, ffmpegErr = exec.LookPath("./ffmpeg")
			}
		}
		if ffmpegErr == nil {
			log.Info("Found ffmpeg", "path", ffmpegPath)
			return
		}
	})
	return ffmpegPath, ffmpegErr
}

// These variables are accessible here for tests. Do not use them directly in production code. Use ffmpegCmd() instead.
var (
	ffOnce     sync.Once
	ffmpegPath string
	ffmpegErr  error
)