feat(meta): use ffmpeg to retrieve album art & metadata

internal/ffmpeg/ffmpeg.go

@@ -0,0 +1,33 @@
+package ffmpeg
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"os/exec"
+)
+
+func ExtractAlbumArt(ctx context.Context, rd io.Reader) (io.Reader, error) {
+	cmd := exec.CommandContext(ctx, "ffmpeg",
+		"-i", "pipe:0", // input from stdin
+		"-an",              // disable audio
+		"-codec:v", "copy", // copy video(image) codec
+		"-f", "image2", // use image2 muxer
+		"pipe:1", // output to stdout
+	)
+
+	cmd.Stdin = rd
+	stdout, stderr := &bytes.Buffer{}, &bytes.Buffer{}
+	cmd.Stdout, cmd.Stderr = stdout, stderr
+
+	if err := cmd.Start(); err != nil {
+		return nil, fmt.Errorf("ffmpeg run: %w", err)
+	}
+
+	if err := cmd.Wait(); err != nil {
+		return nil, fmt.Errorf("ffmpeg wait: %w: %s", err, stderr.String())
+	}
+
+	return stdout, nil
+}