Started the big refactor to extract common logic from engine package (Subsonic only) to core package (more generic)

core/transcoder/ffmpeg.go

@@ -0,0 +1,57 @@
+package transcoder
+
+import (
+	"context"
+	"io"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+
+	"github.com/deluan/navidrome/log"
+)
+
+type Transcoder interface {
+	Start(ctx context.Context, command, path string, maxBitRate int) (f io.ReadCloser, err error)
+}
+
+func New() Transcoder {
+	path, err := exec.LookPath("ffmpeg")
+	if err != nil {
+		log.Error("Unable to find ffmpeg", err)
+	}
+	log.Debug("Found ffmpeg", "path", path)
+	return &ffmpeg{}
+}
+
+type ffmpeg struct{}
+
+func (ff *ffmpeg) Start(ctx context.Context, command, path string, maxBitRate int) (f io.ReadCloser, err error) {
+	args := createTranscodeCommand(command, path, maxBitRate)
+
+	log.Trace(ctx, "Executing ffmpeg command", "cmd", args)
+	cmd := exec.Command(args[0], args[1:]...) // #nosec
+	cmd.Stderr = os.Stderr
+	if f, err = cmd.StdoutPipe(); err != nil {
+		return
+	}
+	if err = cmd.Start(); err != nil {
+		return
+	}
+
+	go func() { _ = cmd.Wait() }() // prevent zombies
+
+	return
+}
+
+// Path will always be an absolute path
+func createTranscodeCommand(cmd, path string, maxBitRate int) []string {
+	split := strings.Split(cmd, " ")
+	for i, s := range split {
+		s = strings.Replace(s, "%s", path, -1)
+		s = strings.Replace(s, "%b", strconv.Itoa(maxBitRate), -1)
+		split[i] = s
+	}
+
+	return split
+}