feat: support S3 media processing pipeline

backend/providers/storage/provider.go

@@ -6,6 +6,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"fmt"
+	"io"
 	"net/url"
 	"os"
 	"path/filepath"
@@ -63,6 +64,44 @@ type Storage struct {
 	s3Client *minio.Client
 }
 
+func (s *Storage) Download(ctx context.Context, key, filePath string) error {
+	if s.storageType() == "local" {
+		localPath := s.Config.LocalPath
+		if localPath == "" {
+			localPath = "./storage"
+		}
+		srcPath := filepath.Join(localPath, key)
+		if err := os.MkdirAll(filepath.Dir(filePath), 0o755); err != nil {
+			return err
+		}
+		src, err := os.Open(srcPath)
+		if err != nil {
+			return err
+		}
+		defer src.Close()
+
+		dst, err := os.Create(filePath)
+		if err != nil {
+			return err
+		}
+		defer dst.Close()
+
+		if _, err := io.Copy(dst, src); err != nil {
+			return err
+		}
+		return nil
+	}
+
+	client, err := s.s3ClientForUse()
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(filePath), 0o755); err != nil {
+		return err
+	}
+	return client.FGetObject(ctx, s.Config.Bucket, key, filePath, minio.GetObjectOptions{})
+}
+
 func (s *Storage) Delete(key string) error {
 	if s.storageType() == "local" {
 		localPath := s.Config.LocalPath